ACD Achievements

Overview

 

Regional and Global Air Quality

 

Influence of Urban Pollution on Regional and Global Air Quality (Influence of Urban Emissions on Atmospheric Composition)

 

Community Involvement and C-130 Deployment (Megacity Impacts on Regional and Global Environments [MIRAGE] Planning)

Instrument Development

Improvements to PeRCIMS instrument

Peroxyacyl Nitrates (PAN) instrument

Actinic flux Spectroradiometer

Analytical Photonics & Optoelectronics Laboratory (APOL) Technology Development in Airborne Observing Systems and Chemical Sensor Systems

Continued Development of a New Laser Spectrometer for High Precision Measurements of 13CO2/12CO2 Isotopic Ratios

Continued Development of New High Performance Airborne DFG Instrument for the Measurement of CH2O

Continued Improvements to Present Airborne TDLAS System Hardware and Software

Community Instruments, Measurement, and Science Support

Chemistry Community Instruments

MSI Group measurement support

Managing the National Science Foundation Atmospheric Chemistry Program

Field Campaigns Complementary to MIRAGE

International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)

NASA The Intercontinental Chemical Transport Experiment (INTEX-NA)

NOAA New England Air Quality Study – Intercontinental Transport and Chemical Transformation (NEAQS-ITCT 2004) (formerly Northeast-North Atlantic [NENA] 2004)

Measurement of Pollution In The Troposphere (MOPITT)

MOPITT Accomplishments

Operational Data Production

MOPITT Data Validation

MOPITT Education and Outreach

MOPITT Science Studies

MOPITT Participation in INTEX-A

Long-range Transport of CO Emissions from Russian Fires

The CO Budget over Europe

Pollution from Mega-Cities

Involvement with Other Satellite Missions

Seasonal and Inter-Annual CO Variability

Data Assimilation and Inverse Modeling

Comparison of CO and Aerosol Emissions from Biomass Burning

Photochemistry

Peroxy Radical Studies

PANS

Formaldehyde (CH2O)

Radiation

Regional and Global Chemical Transport Models and Air Pollution Studies

Weather Research Forecasting with Chemistry (WRF-Chem)

HANK Regional Transport Model

Global chemical transport models and air pollution studies

 

Reactive Carbon Research

 

Emissions of Primary Organic Compounds

Reactive Carbon Species as Sources and Reservoirs of Radical Species

Oxygenated Volatile Organic Carbon (OVOC) Contribution to the HOx Cycle

Gas-aerosol Partitioning of Organic Species

Laboratory Kinetics

Oxidation Pathways for Alkyl Iodides

Nitrate Production from Toluene Oxidation

Oxidation Mechanisms of Methyl Formate and Methyl Acetate

 

Multiphase Processes in the Troposphere

 

Aerosols

Clouds – Cloud Chemistry Modeling

Effect of boundary layer processes on chemical species distributions -Segregation of Chemical Reactants in a Shallow Cumulus Boundary Layer

WRF-AqChem, a coupled meteorology and multi-phase chemistry model- Development and Initial Results of Model

Intercomparison of Convective Cloud Chemistry Models

Cloud Chemistry Process Studies - The Importance of the Cloud Drop Representation on Cloud Chemistry

Snow/Ice

Mid-latitude Snow Chemistry Experiment

Deployment of a Snowpack UV Radiation Profiler to Summit, Greenland

Antarctic Polar Plateau

 

Chemistry in the Climate System

 

Climate Simulations

 

Present-Day Climate

Tropospheric ozone interannual variability

Studies of the Arctic Oscillation

Role of convective versus synoptic transport

SANTA FE project

Past and Future Climates

Intergovernmental Panel on Climate Change (IPCC) simulations

Model Development

Off-line Community Atmosphere Model (CAM)

Interactive Community Atmosphere Model (CAM3)

MOZART-4

Tracer Version of MOZART-4

Adjoint Version of MOZART

 

Biogeochemical Cycles

 

Laboratory Studies

U.S. Field Studies

International Field Studies

Regional Modeling Studies: U.S.

Regional Modeling Studies: International

Global Modeling Studies

Model and Database Development

Instrument Development

 

Integrated Study of Dynamics, Chemistry, Clouds, and Radiation of the Upper Troposphere and Lower Stratosphere (UTLS)

 

Satellite Data Analysis

Model Development

UTLS Chemistry and Aerosols

Instrument Development

Trace Organic Gas Analyzer (TOGA):  Measurements, Standards, and Intercomparisons (MSI) Group

NO/NOy and O3:  AON Group

HIAPER Radiation Package (HARP):  ARIM Group

Development of autonomous actinic flux instrumentation for high altitude aircraft – NASA WB-57

Chemical Ionization Mass Spectrometer (CIMS): LK Group in collaboration with Georgia Institute of Technology (GIT)

Development of a prototype HIAPER OH instrument

Fourier-Transform Infrared (FTIR) Spectrometer for HIAPER

 

Middle Atmosphere Science

 

WACCM - model development and results

Impacts of El Niño-Southern Oscillation (ENSO) on the middle atmosphere

Seasonal variability of trace species in the UTLS region

Stratospheric influence on seasonal cycles of tropospheric tracers

Monsoon impacts on stratosphere/troposphere exchange (STE)

Parameterization of gravity wave fluxes due to convective excitation

Stratospheric trends in temperature and water vapor

Chemical transition across the extratropical tropopause

Structure and variability of the SE Asia monsoon system

Mesospheric Processes

Chemistry of the middle atmosphere sodium layer

Atmospheric Tides

Oxygen – hydrogen chemistry and emissions in the mesosphere

HIRDLS

Pre-launch Activities

Instrument

Algorithm Development

Post-launch activities

 

Strategic Initiatives

 

Biogeosciences

 

Executive Summary

BGS Achievements (Division Narratives)

 

Atmospheric Chemistry Division: ACD

Carbon-Nitrogen cycling (Tasks 1 & 2)

Laboratory studies (Task 2)

U.S. field studies (Task 2)

International field studies (Task 2)

Regional modeling studies, U.S. (Task 2)

Regional modeling studies, International (Task 2)

Global modeling studies (Task 1)

Model and database development (Tasks 1 & 2)

Instrument development (Task 2)

Climate and Global Dynamics Division: CGD

Community land model (Tasks 1 & 4)

Land cover and land use change (Tasks 1 & 4)

Development of carbon and nitrogen capabilities in CLM (Task 1)

Community land model diagnostics package (Task 1)

First results from CCSM3 with coupled C and N cycles (Task 1)

Multi-century carbon cycle simulations (Task 1)

Coupled climate carbon cycle model intercomparison project (C4MIP) (Task 1)

High-resolution carbon cycle model user interface project (Task 1)

Mineral Aerosols in CCSM (Tasks 1 & 4)

Carbon in the Mountains Experiment:  CSME and ACME

Carbon in the mountains experiment (CME) (Tasks 2 & 3)

Airborne carbon in the mountains experiment (ACME I) (Tasks 2 & 3)

CO2 transport over complex terrain (Tasks 2 & 3)

Atmospheric Technology Division:  ATD

Airborne CO2 Measurements (Task 2)

Tower CO2 measurements: autonomous inexpensive robist CO2 analyzer (AIRCOA) (Task 2)

NCAR CO2 and O2 calibration facility (Task 2)

Synthesis of global light aircraft CO2 data (Task 2)

Wisconsin Tall-tower atmospheric O2 measurements (Task 2)

BGS Publications

Refereed

In review or in press

Non-refereed

 

Wildfires

 

Laboratory Studies

International Field Study

Modeling Studies

 

UTLS

 

MIRAGE

 


Overview

The ACD (Atmospheric Chemistry Division) mission is (1) to understand the chemical composition of the atmosphere, the processes that modify and control the composition, and potential changes that may result from natural and human induced forcings; (2) to provide relevant, reliable, accessible, unbiased, and timely information on atmospheric chemistry to government and society; and (3) to act as an intellectual resource and enabler to the wider atmospheric sciences community through the development of new measurement capabilities and methodologies, development and application of numerical models that reliably simulate present and future atmospheric conditions, and the planning and execution of field experiments to address specific scientific questions of regional and global significance. 

Over the next few years, ACD staff will direct their research efforts at two grand challenges that confront society and where atmospheric chemical processes play a crucial role, namely Regional and Global Air Quality and Chemistry in the Climate System.  The directions and priorities of the division’s research efforts have been chosen for their societal relevance and scientific merit.  These plans were developed and formalized in the ACD Science Plan and were developed with the recognition that the accomplishment of any of the major goals will require significant collaboration with other NCAR divisions and with the university community.  The goals were determined as a result of an iterative process involving the division director, the division internal management and external advisory committees.

The main goal for Regional and Global Air Quality is to understand and quantify the impact of urban emissions on air quality. Priority will be given to studying the large-scale impacts of intense emissions originating from megacities, and the multiphase (gas-aerosol-cloud) processes that transform pollutants in the atmosphere. The goals for Chemistry in the Climate System are to understand the interactions between the physical climate system, the chemical climate system, and the biosphere. Priority will be given to the simulation of the recent past and future chemical climate states based on current climate simulations and to the study of the crucial role of the upper troposphere/lower stratosphere (UTLS) in the physical and chemical climate system.

The two primary research areas, Regional and Global Air Quality and Chemistry in the Climate System, encompass the research areas outlined in the 2003 ACD program plan.  The table below shows the relationship between the 2003 ACD Program Plan, the ACD Science Plan, and the 2004 ACD Program Plan.

ACD Program 2003

Themes and Priorities in ACD Science Plan

ACD Program 2004

Atmospheric Trace Gases

Tropospheric Photo-oxidants

Regional and Global Air Quality

Influence of urban emissions on regional and global air quality

Reactive carbon research

Multiphase processes in the troposphere

Regional and Global Air Quality

Chemistry climate interactions

Biogeochemical cycles

Chemistry in the Climate System

Coupled chemistry-climate modeling studies

Biogeochemical cycles

Tropospheric Chemistry Climate Studies

 

Stratospheric ozone and UV-B

Integrated study of dynamics, chemistry, clouds, and radiation of the Upper Troposphere and Lower Stratosphere

Middle atmosphere studies

UTLS and Middle Atmosphere Studies

 

Regional and Global Air Quality

Characterization of air quality is an important issue, not only in urban areas, but also on regional and global scales.  Satellite, aircraft, and ground-based observations throughout the global atmosphere are confirming that air pollution can be transported over large distances, e.g., from eastern Asia to the western U.S., from North America to Europe, and from mid-latitudes to the Arctic.

Discussions of air quality generally center on issues related to atmospheric oxidants and particulates.  Increases in ozone are of particular concern as this compound may impact humans and natural ecosystems, and is currently ranked as the third most important “greenhouse” gas.  Thus, future trends in its concentration have strong links to both global air quality issues and to climate change.  Potential global changes in OH radical concentrations are another major concern.  OH is responsible for initiating the oxidation of many compounds emitted to the atmosphere into more soluble species that are removed from the atmosphere by wet and dry deposition or adsorbed into aerosols in multiphase processes.  Critical challenges within the context of global change will be to determine if the capacity of the atmosphere to remove these gaseous species will be reduced or if climate change will affect the oxidation or emission processes and lead to significant change in the chemical composition of the troposphere. 

There is ample evidence for increases in oxidants and other pollutants in urban and regional environments, where air quality is a major issue.  Furthermore, transport of ozone and some ozone precursors from densely populated areas has led to increases on the global scale (estimated at 30% since the preindustrial era), and larger increases are expected with the demands of population growth.   One of the major research themes within ACD is to investigate the influence of the export of urban pollution on regional and global air quality.

Reactive carbon species, also referred to as volatile organic compounds (VOC), play a central role in determining tropospheric air quality.  Primary VOC emissions are extremely diverse chemically, with both natural and anthropogenic sources, and range in complexity from simple gases such as CO and methane to more complex chemical forms like the terpenes (naturally-occurring isomeric compounds of general formula C10H16).  Once in the atmosphere, these gases are oxidized to more soluble forms (carbonyl compounds, organic nitrates, organic acids, multi-functional species, etc.) that are more readily removed from the atmosphere by deposition, or that can couple back into the HOx and NOx chemical cycles - often at significant distances from the original source regions.  The cycle of VOC emission, transformation, and heterogeneous loss is a major topic of research within ACD.

Multiphase processes (gas-aerosol-cloud interactions) are increasingly recognized as important to tropospheric air quality.  High particulate concentrations, now common in and around urban centers but increasingly present on continental scales, pose a significant health risk.  Many aerosols serve as cloud condensation nuclei and therefore influence cloud particle properties (e.g., albedo) and precipitation.  They also scatter or absorb light, thus altering the atmospheric radiation field and reducing visibility.  In addition, particles can act as sinks for some atmospheric oxidation products including sulfuric and nitric acid, ammonia, and many products of reactive carbon oxidation.  Clouds also influence both tropospheric air quality and climate through their impact on the hydrologic cycle, as transporters, processors, and scavengers of pollutants, and via their effects on the tropospheric radiation field.  Convective clouds play a particularly important role as transporters of trace species from the polluted boundary layer to the upper troposphere, which enhances ozone production in the upper troposphere where absolute changes in ozone have their largest radiative impact.  Elucidation of the many complex physical/chemical processes involved in the multiphase chemistry of the troposphere - from particle nucleation and growth, to impacts of aerosols on gas phase composition, and the impacts of clouds as transporters and processors of trace gases is a major focus of ACD research activity.

 

Influence of Urban Pollution on Regional and Global Air Quality (Influence of Urban Emissions on Atmospheric Composition)

ACD efforts in this area include planning for the MIRAGE-Mex (Megacity Impacts on Regional and Global Environments, 2005 Mexico City campaign) field campaign, development of instruments to be used for tropospheric chemistry studies, development and deployment of community instruments and continued measurement support, participation in field campaigns that are complementary to MIRAGE, improvements to and use of MOPITT (Measurements of Pollution In The Troposphere) retrievals, photochemical research, and development and use of regional chemical transport models.

 

Community Involvement and C-130 Deployment (Megacity Impacts on Regional and Global Environments [MIRAGE] Planning)

While the importance of urban pollution to regional and global environments is widely acknowledged, it remains poorly quantified because of the complexity of physical and chemical processes that must be understood over a broad span of spatial and temporal scales. 

The MIRAGE program is a new activity under development by scientists at NCAR and the university community, based on the recognized need for an integrated, multidisciplinary approach to this complex environmental issue.  Planning is underway for a major field campaign in Mexico City in 2005 (MIRAGE-Mex).  Sasha Madronich, Frank Flocke, and John Orlando were involved in preparing and submitting a MIRAGE-Mex proposal to NSF.  The proposal will be reviewed by the National Science Foundation’s Observing Facilities Advisory Panel (OFAP) in April 2005.  Additional information on MIRAGE-Mex logistical and scientific planning is found below under the Strategic Initiatives – MIRAGE section.

 

Instrument Development

A number of instruments have been developed or improved by ACD staff for use in tropospheric chemistry studies.  These include the Peroxy Radical Chemical Ionization Mass Spectrometer (PeRCIMS), peroxyacyl nitrates (PAN), radiation, isotopes, and formaldehyde instruments.

 

Improvements to PeRCIMS Instrument

Chris Cantrell of the Atmospheric Radical Studies (ARS) Group has developed an instrument to measure peroxy radicals in the atmosphere.  The PeRCIMS instrument operates on the principle of chemical conversion of ambient or calibrator-generated peroxy radicals to gas-phase sulfuric acid, followed by chemical ionization by reaction with negatively charged nitrate ions, and separation and detection of the ions via mass spectrometry.  Signals for the total peroxy radical concentration [HO2+RO2] and for the hydroperoxy radical concentration [HO2] have been acquired by greatly changing the concentration of the reagent gases, nitric oxide (NO) and sulfur dioxide (SO2).  For HO2+RO2 measurements, the reagent concentrations in the inlet were in the tens of ppmv range.  For HO2 measurements, they were in the thousands of ppmv range.  This necessitated the use of pure NO and pure SO2 for the HO2 quantification.  Recently, we have investigated the use of oxygen or nitrogen dilution as an alternative to changing the reagent gas concentrations.  The separation of HO2 and RO2 exploits the competition between the reaction of alkoxy radicals (RO), which are generated in the reaction of RO2 with NO, with oxygen and NO.  When RO radicals react with oxygen, HO2 is usually a product (depending somewhat on the structure of RO), which leads to measurement of the RO2.  When RO radicals react with NO, alkyl nitrate stable products (RONO) are formed, which leads to RO2 not being measured.  Thus, the parameter which affects the sensitivity to RO2 is the NO/O2 ratio.  At low NO/O2 values, RO2 radicals are measured efficiently, and at high values they are not.

Dilution of ambient air in a ratio of 1:10 with either oxygen or nitrogen leads to modulation of the oxygen concentration by a factor of 49, allowing RO2 measurements with high efficiency (>80%) in the HO2+RO2 mode or fairly low efficiency (<30%) in the HO2 mode.  The non-ideal responses (100% and 0% in the two modes, respectively) can be corrected using laboratory measurements of RO2/HO2 response factors and model estimates of the makeup of RO2 species.  Comparisons of the reagent gas concentration change versus the oxygen modulation method were performed in the laboratory, and representative results are shown in Figure 1, along with a numerical model of the expected results.  These preliminary results are promising, and suggest that the oxygen modulation technique may be nearly as efficient at separating HO2 and RO2, with the advantage that change between the two modes of operation can be accomplished quickly.  Development will continue in FY05, with a design goal to quantify atmospheric HO2 and HO2+RO2 within one minute.  This will require modifications to the inlet and the computer control software.

Figure 1: Measured and modeled response of PeRCIMS to RO2 radicals versus the ratio of the concentrations of NO to O2.  The large colored triangles show normal operating conditions using the method of changing reagent concentrations.  The large colored squares show potential operating conditions using oxygen dilution modulation.  Open circles show laboratory measurements of sensitivity for other operating conditions, using changing reagent concentrations.  The lines represent models of the sensitivity of RO2 when changing reagent concentrations (blue shades) and oxygen dilution modulation (green shades).  The different curves correspond to different SO2/NO ratios, in which the chain length (CL) is the SO2/NO ratio divided by five.  Implicit in the model is an assumption about the rate of the reaction of RO with SO2 to form HO2 (inferred from laboratory studies).

 

Peroxyacyl Nitrates (PAN) instrument

Frank Flocke and Aaron Swanson (University of Colorado, Boulder (CU); NOAA Aeronomy Laboratory) flew a new instrument for fast (1-2 sec), continuous measurements of PAN and related species on the NOAA P-3B aircraft as part of the NOAA-led International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) and New England Air Quality Study (NEAQS) programs.  The instrument, called PAN-CIGAR (PAN-CIMS [Chemical Ionization Mass Spectrometer] Instrument by Georgia Institute of Technology [GIT] and NCAR), has been a joint development with Greg Huey and David Tanner (GIT).  Prior to deployment, much of the year was spent on redesigning a prototype instrument to make it ready for unattended aircraft operation.  The pump system was redesigned and gas loads were lightened.  The operation and data acquisition software was improved as well as some electronics to allow unattended operation and controlled recovery from power outages, etc.  Additional instrument characterization (investigation of the sensitivity dependence on humidity, flow, and pressure) was performed.  Other instrument improvements were made with help from David Hanson (ACD).  From October 2003 to early April 2004, Sandra Lopes, a graduate student from the University of Wiesbaden, Germany worked with Swanson and Flocke.  She successfully completed her Master’s degree in Chemical Engineering with them by participating in the development and construction of a new in situ calibration source for the instrument, a unit that is 50% smaller than the old unit and has augmented control capabilities for use with PAN-CIGAR.

 

Actinic Flux Spectroradiometer

Members of ACD’s Atmospheric Radiation Investigations and Measurement (ARIM) Group, Rick Shetter, Sam Hall, Barry Lefer, and Edward Riedel, developed a new generation actinic flux spectroradiometer.  The ARIM Group has deployed ground-based and airborne Scanning Actinic Flux Spectroradiometer (SAFS) instruments for the determination of actinic fluxes and photolysis frequencies for the last seven to eight years.  These have operated well, but have limited time resolution (~10 seconds for a spectrum) and require frequent calibration and maintenance.  A new instrument based on a monolithic monochromator with a UV-enhanced windowless CCD detector has been developed. This instrument is smaller and lighter with a new PC-104+ data acquisition and control system. The instrument has been quite reliable and has the ability to collect actinic flux spectra from 280 to 680 nm at 1-10 Hz, allowing for fast photochemistry investigations. The smaller design will allow deployment on aircraft platforms with limited space for instruments and operators including the NSF HIAPER (High-performance Instrumented Airborne Platform for Environmental Research) aircraft and future Unmanned Aerial Vehicles (UAV) platforms. One of these new generation instruments was deployed on the NASA DC-8 for the INTEX-NA experiment.

 

Analytical Photonics & Optoelectronics Laboratory (APOL) Technology Development in Airborne Observing Systems and Chemical Sensor Systems

Alan Fried, James Walega, and Dirk Richter of the joint Atmospheric Technology Division (ATD)/ACD APOL have developed and improved several instruments.

 

Continued Development of a New Laser Spectrometer for High Precision Measurements of 13CO2/12CO2 Isotopic Ratios

The Annual Scientific Report (ASR) last year described this project in detail along with progress achieved in designing and constructing the new instrument (APOL_(ACD/ASR03)).  Figure 2, which illustrates a modified version of the optical setup shown last year, has been constructed and a number of tests have been carried out. This new setup allows the sample and reference beams to make two traversals of the absorption cells for improved measurement precision. As discussed in our previous ASR, the absorption signals from the two cells containing the sample gas and an isotopic reference standard are rapidly compared using online fitting analysis. The fitting procedures have been developed and wait further testing on CO2 absorption features, which should take place within the next month or two.


Figure 2: Optical schematic of modified Differential Frequency Generator (DFG)-based system for high precision carbon dioxide isotopic ratio measurements. 

 

Figure 3 shows the design of the inlet system, which represents the second major task associated with high precision CO2 measurements. This system, which is in the testing phase, allows various combinations of reference standards and ambient samples to be introduced to the absorption cells under closely matched conditions of pressure and flow. Other studies frequently do not take such precautions.

 

 

Figure 3: Schematic of inlet and outlet plumbing system. The two absorption cells are designated by Abs Cell A and B in this figure.

 

As in the previous year, the APOL Group worked in close collaboration with NCAR’s Education and Outreach Program to host two teachers and students from local area high schools to help with all phases of this project. The following Web link (http://www.atd.ucar.edu/apol/biocomplexity.htm) further describes the full project and also shows one important aspect of the teacher and student involvement: organization and dissemination of the material to the broader public.

 

Continued Development of New High Performance Airborne DFG Instrument for the Measurement of CH2O

As discussed in last year’s ASR, the trace gas CH2O is one of many important atmospheric trace species involved in ozone production and radical formation. The APOL Group has been actively involved in a long-term effort to carry out ever more accurate and precise measurements of this gas throughout the troposphere and lower stratosphere.  As discussed previously, such measurements have been exclusively acquired using the APOL Group’s liquid-nitrogen cooled tunable diode laser absorption spectroscopy (TDLAS) system.  Although the Group has continued to implement a number of significant improvements to this system in terms of hardware and software (to be discussed below) and achieved consequent gains in instrument performance, the Group is fast approaching an ultimate limit to such gains.  The present instrument sensitivity (15 – 50 pptv, 1s precision for 1 minute of averaging) needs to be further improved for routine CH2O measurements in the background atmosphere, particularly in the upper troposphere/lower stratosphere where CH2O decomposition becomes a major source of reactive hydrogen radicals.  In addition, the instrument is large and requires periodic operator intervention.  To address this critical need as well as the need to develop smaller, lighter, and autonomous-operation instruments for future HIAPER campaigns, the APOL Group has been developing a new high performance airborne CH2O instrument based upon difference frequency generation.  A comprehensive description of this approach, as well as its many advantages over lead-salt TDLAS systems, has been discussed in last year’s ASR and will not be repeated here.  (“Technology Development in Airborne Observing Systems and Chemical Sensor Systems,” at TDLAS_(ACD/ASR03)).

However, for size comparison purposes, APOL Figures 3 and 4 show the present airborne TDLAS system and the compact new DFG system.  The Herriott absorption cells in both systems are approximately the same size.  With this in mind, a comparison of these two figures immediately reveals that the DFG system is significantly smaller than the TDLAS system; the DFG-Herriott cell configuration in Figure 5 has replaced the entire optical setup of the TDLAS system in Figure 4.  A further advantage of the DFG system is that no liquid cryogens are required, in stark contrast to the present TDLAS system.  Although laboratory tests with the new DFG system are not yet complete, evidence strongly indicates that this new system will ultimately achieve higher performance than the TDLAS system for CH2O and other molecules.

   
 

 


Figure 4: Schematic of optical system with cutaway view of temperature-stabilized enclosure employed during INTEX-A. Two separate laser channels with separate beam collection optics are shown. However, during INTEX-A only one laser channel was employed. The enclosure dimensions are approximately 33” long x 24” wide x 12” high.

 

 

Figure 5: Photograph of the APOL Group’s DFG stage mounted to a new, more stable Herriott cell. The size of the DFG stage with enclosure is 7”long x 9.5” wide x 3.5” high. For comparative purpose, the cell here is the same size as the cell in Figure 4. 

 

Continued Improvements to Present Airborne TDLAS System Hardware and Software

 

Despite the significant progress achieved in the DFG development, the laboratory prototype system has not yet been tested on airborne platforms. Rather than risk flying such a system for the first time during a critical field mission, the APOL Group decided to pursue the more prudent course of action by employing the TDLAS system during the 2004 summer INTEX-NA study. However, numerous small modifications were implemented to this system this past year to further improve the system robustness, reliability, and performance.  Many of these modifications, which are too numerous to list here, focused on improving the optical-mechanical stability of the system.  In addition, numerous software changes were also implemented for improved performance, reliability, and enhanced data quality assurance.

 

Community Instruments, Measurement, and Science Support

ACD supports several analytical instruments that are available by request from the community to support airborne field campaigns.  These include instruments to measure carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), and water vapor (H2O).  Teresa Campos (ACD/ATD) is responsible for the maintenance, deployment, data collection, and data reduction for these instruments.  ACD also supports ongoing hydrocarbon calibration efforts by Eric Apel.

 

Chemistry Community Instruments

Teresa Campos and Sam Hall of the ARIM Group were responsible for instrument preparation and calibration, data acquisition software development, instrument deployment, and data analysis during several field campaigns.   Preliminary results from the Gulf of Tehuantepec (GOTEX) airborne field experiment, conducted in the Eastern Pacific marine boundary layer near Salina Cruz, Mexico, indicate successful measurement of CO2 air-sea exchange by the eddy covariance method.  The sensitivity to aircraft acceleration was quantified and found to contribute to the flux signal only at frequencies less than 2 Hz.  Even at these frequencies, however, the amplitude of the artifact is a factor of 50 smaller than equivalent power spectral content of ambient marine boundary layer data measured at the same altitudes, as shown in Figures 6 and 7. 

 

 

Figure 6:  Power spectral distribution of  two-minute ambient CO2 measurements of marine boundary layer air during the 2004 Gulf of Tehuantepec Experiment.  Observations were made at 380 msl off the coast of Salina Cruz, Mexico.

 

 

Figure 7: The power spectral distribution of a two-minute time series during which CO2 calibration gas was sampled in-flight at 380 msl in the marine boundary layer.  The measurement represents a quantification of the spectral dependence of the air motion sensitivity of the CO2 sensor.

 

A collaboration between the Atmospheric Technology Division, the Atmospheric Chemistry Division, and the Biogeosciences Initiative has been in place for several years to fund development and field support of airborne facility in situ trace gas instruments.  Supported developments include water vapor and fast-response ozone measurements in addition to carbon dioxide and carbon monoxide.  The activities have been successful on several fronts in maintaining and improving the quality of requestable instrumentation and data sets. 

The airborne CO2 instrument was modified to enable flux measurements by the eddy covariance method.  Assessment of measurement capabilities was assessed by using the instrumentation on the GOTEX experiment (Kenneth Melville [Scripps Institution of Oceanography], Carl Friehe [University of California, Irvine]) and the Airborne Carbon in the Mountains (ACME) experiment (Russell Monson [CU], David Schimel, Jielun Sun, and Britton Stephens, [NCAR’s Climate and Global Dynamics [CGD] Division).  Spectral analysis of GOTEX marine boundary layer data imply an instrument frequency response of 4-Hz, and time series analysis implied a mixing ratio measurement precision of 0.2 - 0.3 ppmv (1-s for a 1-second average).  The flux artifact of this sensor due to air motion sensitivity was quantified in both marine and terrestrial boundary layer environments during both missions by introduction of calibration gas into the sample cell during a portion of a boundary layer transect.  A small artifact due to correlated air motion sensitivity was observed in GOTEX data at frequencies lower than 2 Hz.  However, the amplitude of these fluctuations is a factor of 50 smaller than the equivalent power spectral content of ambient data obtained in the marine boundary layer at the same altitude.  Preliminary ACME results from intercomparison to analyses of flask samples by Heather Graham and Ralph Keeling (Scripps Institute of Oceanography), imply an accuracy of ± 0.2 ppmv.  This result has been reproduced by intercomparison to CME ground network working standards provided and analyzed by the CO2 calibration facility by Britton Stephens (UCAR/RAF).

The commercial NCAR open-path diode laser absorption hygrometer was modified to improve accuracy of lower tropospheric water vapor mixing ratio observations and to increase the time response of the instrument from an 8-Hz sampling rate to 18-Hz.   The modified laser hygrometer performed well as an experimental measurement on the second Alliance Icing Research Study (AIRS-II) and GOTEX experiments.  Results from the AIRS-II mission established confidence in the accuracy of clear sky water vapor measurements to be +/- 5%, relative to chilled mirror sensors on the same platform.  Preliminary results from the GOTEX data have confirmed the capability of this sensor to measure vertical fluxes by the eddy covariance method.  Spectral analysis of 18-Hz data from boundary layer transects agree well with lyman alpha hygrometer data.

To increase confidence in the absolute accuracy of all NCAR facility water vapor measurements, an accurate, large dynamic-range water vapor calibration system was purchased.  This commercial system includes a humidity generation system and a certified reference sensor with traceability to both the U.S. and U.K. standards organizations.  Both cover a dew point range of -80º to +20º C, and the reference sensor accuracy is ± 0.1º C in the -60º to +20º C range and ± 0.2º C in the -80º to -60º C region.  This facility is a crucial component of ensuring accuracy of water vapor measurements both in the troposphere and UTLS regions.

 

MSI Group Measurement Support

For the past decade Eric Apel of the Measurements, Standards, and Intercomparisons (MSI) Group has played a leadership role in community measurement support activities. These include supplying the community with primary calibration standards, conducting informal intercalibration exercises, and organizing and conducting formal intercomparisons of research instrumentation.

As part of the MSI Group’s continuing effort in community measurement support activities this year, Apel prepared and provided a primary standard which was used by all research groups involved with the measurement of volatile organic compounds during the ICARTT campaign. The standard contained the following compounds: Methane, CO, ethane, acetylene, ethane, propene, propane, butane, 134A, benzene, toluene, acetone, acetonitrile, carbon tetrachloride, chlorofluorocarbon (CFC) 113, and iso-propyl nitrate. The MSI Group received assistance from Steve Montzka and Paul Novelli at NOAA’s Climate Monitoring and Diagnostics Laboratory (CMDL) and Elliot Atlas of the University of Miami in the calibration of specific compounds in the standard.

In addition, Eric Apel, along with Alan Fried of ACD/ATD, organized and will convene a special session on “Tropospheric Photochemistry” at the annual AGU meeting in December.

This year the MSI Group also contributed to an ACD document outlining plans for a community facility to be housed in the new ACD building. This community facility would focus on chemical instrument calibration and validation, which are clearly-perceived needs in the community and a natural outgrowth of this Group’s past and ongoing community support activities. It is necessary to quantify measurement uncertainties for instrumentation involved in key atmospheric experiments in which results have implications for local and national policy decisions. Kuster et al., 2004, documents an intercomparison study that the MSI Group participated in during Texas Air Quality Study (TEXAQS) 2000, a study that clearly has policy implications. 

Managing the National Science Foundation Atmospheric Chemistry Program

Chris Cantrell accepted a temporary assignment with the National Science Foundation to help manage the Atmospheric Chemistry Program.  This was implemented under the Intergovernmental Personnel Act (IPA), in which persons “rotate” from their home institution for a period of time (usually one to three years) to perform services needed by the Federal government.  The Atmospheric Chemistry Program at NSF considers ad hoc proposals from the community to investigate problems related to atmospheric composition (gas phase and condensed phase), transport and transformation, interaction between ecosystems and the atmosphere, and connections between chemistry and climate through theoretical, observation, and laboratory investigations.  The program considers 150-200 proposals per year, which are each reviewed by four to six experts in the particular field of study, and the most meritorious are awarded funding.  Many projects are at the boundaries of atmospheric chemistry and other disciplines (e.g., climate, meteorology, Arctic or Antarctic science, oceanography, international), and as such are reviewed by two or more programs.  The assignment allowed a unique look at the federal process of funding scientific research, in particular the NSF process, and enabled Cantrell to become more familiar with the persons and activities in the atmospheric chemistry field.  The goal of the IPA program is for rotators to bring back to their home institution the information gained in order to improve the relationship with the agency.

There were also many opportunities to interact with representatives of other domestic and foreign agencies.  These processes can lead to enhanced interactions, and leveraging of limited funds that could enhance the outcomes of our investment in scientific research.

NSF also places a considerable emphasis on the “broader impacts” of scientific research.  Thus, given a project with high priority scientific goals, and reasonable chances of success, the principal investigator would be expected to contribute to the wider aspects of science including education and training activities that are integrated with the research, broader participation of underrepresented groups, enhance infrastructure, wide dissemination, and provide benefits to society.  Program officers at NSF examine the balance between the intellectual merit of quality, high priority scientific projects, and their contribution to these broader issues. 

Field Campaigns Complementary to MIRAGE

ACD scientists from the ARIM, APOL, AON (Atmospheric Odd Nitrogen), and STM (Stratospheric/Tropospheric Measurement) Groups participated in two field campaigns in the summer of 2004, which were under the auspices of the ICARTT field campaign.  These campaigns were clearly complementary to the objectives of MIRAGE (see Strategic Initiatives-MIRAGE section below) and the results will provide an improved understanding of pollution transport across the U.S. and the northern Atlantic to Europe.

 

International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)

Several groups in North America and Europe independently developed plans for field experiments in the summer of 2004, designed to provide improved understanding of the factors that shape air quality in their respective countries and the remote regions of the North Atlantic.  NASA and NOAA conducted experiments under the INTEX-NA and the NEAQS - ITCT (Intercontinental Transport and Chemical Transformation) 2004 programs respectively.  The Europeans (U.K., Germany, and France) organized coordinated studies under Intercontinental Transport of Pollution (ITOP).  While each of these programs has regionally focused goals and deployments they share many of the same goals and objectives and the proposed study areas overlap significantly.  ICARTT was formed to take advantage of this synergy by planning and executing a series of coordinated experiments to study the emissions of aerosol and ozone precursors their chemical transformations and removal during transport to and over the North Atlantic.  The capabilities represented by the consortium will allow an unprecedented characterization of the key atmospheric processes.  Several ACD groups participated in INTEX-NA and NEAQS-ITCT 2004 as described below.

 

NASA Intercontinental Chemical Transport Experiment (INTEX-NA)

INTEX-NA was a major NASA science campaign to understand the transport and transformation of gases and aerosols on transcontinental and intercontinental scales and their impact on air quality and climate.  A particular focus of INTEX-NA was to characterize and quantify the inflow and outflow of pollution over North America.  Measurements from INTEX-NA will also provide important validation of satellite observations with ongoing satellite measurement programs, such as Terra, Aura, and the European Space Agency’s (ESA) Envisat (Environmental Satellite). The experiment was conducted over the continental United States during the summer of 2004 using a variety of science aircraft. 

The ARIM Group deployed two SAFS systems on the NASA DC-8 aircraft to measure the in situ total spectral actinic flux as a function of wavelength and calculate the in situ photolysis frequencies of 23 important photochemical reactions.  Results are discussed in the Photochemistry/Radiation section below. 

The APOL Group deployed the modified TDLAS system on the NASA DC-8 to measure formaldehyde (CH2O). The instrument improvements worked extremely well in all respects, and this allowed the Group to successfully acquire ambient CH2O measurements on 19 out of the 20 mission flights.  Preliminary results are discussed in the Photochemistry/Formaldehyde section below.

 

NOAA New England Air Quality Study – Intercontinental Transport and Chemical Transformation (NEAQS-ITCT 2004) (formerly Northeast-North Atlantic [NENA] 2004)

NOAA's Health of the Atmosphere research is focused on the atmospheric science that underlies regional and continental air quality, with the goal of enhancing the ability to predict and monitor future changes. Under this program NOAA organized the NEAQS-ITCT 2004 campaign with the P-3B aircraft and NOAA research vessel Ron Brown operating out of New Hampshire.  The study focused on air quality along the Eastern Seaboard and transport of North American emissions into the North Atlantic.

The AON Group deployed the PAN-CIGAR to measure PAN and related compounds.  These measurements are a crucial part of evaluating photochemical processing and the influence of natural and anthropogenic hydrocarbons.  Initial results are discussed in the Photochemistry/PAN section below.

Also, as a contribution to the NEAQS program, a sensitive NO instrument that the AON Group had previously flown on aircraft was modified and lab-tested to loan to Alex Pzenny (University of New Hampshire) and Eric Williams (NOAA Aeronomy Laboratory) for use at one of the ground sites.

The STM Group deployed a Whole Air Sampler on the P-3B to collect air samples for analysis of hydrocarbons, halocarbons, alkyl nitrates, and CO.  These measurements are required to adequately assess photochemistry and transport.  Sample analysis was recently completed and data quality control and analysis is currently underway.

 

Measurement of Pollution In The Troposphere (MOPITT)

The MOPITT experiment has provided atmospheric scientists with the first multi-year, global view of carbon monoxide (CO) profile concentrations in the troposphere. The experiment is approaching the five-year anniversary of its launch on the Terra satellite in December, 1999. With this, the project at NCAR will pass a milestone, with the completion of the initial phase that began more than 10 years ago. During this period the data processing software was developed and the first years of orbital data processed, validated, archived, and provided to the atmospheric chemistry community, as well as being used for scientific research. The mission is a joint Canadian-U.S. effort, and ACD is responsible to NASA for the continued development of the data reduction algorithms and for operational data processing at every stage from instrument counts to calibrated radiances, through to globally retrieved CO vertical profiles and total columns.  MOPITT Version 3 validated tropospheric CO profiles are currently being processed and delivered to NASA for use by the international community. This is the first dataset of its kind, and represents a significant advance in satellite remote sensing of the troposphere. The next phase of the core effort will concentrate on some additional improvements to the retrieval algorithms, as well as continuing with the scientific applications of the data.

The MOPITT Group has been active in 3 main areas this year: (1) continued improvement of the data reduction algorithms in preparation for Version Four, data processing, and delivery of the final products to NASA for later distribution to the community; (2) support of aircraft field campaigns; and (3) use of the MOPITT data in tropospheric chemistry and transport studies. More information about the MOPITT project can be found at http://www.eos.ucar.edu/mopitt/ and http://www.atmosp.physics.utoronto.ca/MOPITT/home.html.

 

MOPITT Accomplishments

 

Operational Data Production

The NCAR MOPITT team, led by John Gille, has been engaged in the ongoing data reduction process to produce geophysical quantities for scientific use by the community from the instrument count data. The elements of this processing capability and the people responsible, are the data handling interfaces and protocols between NCAR and the NASA centers which receive and archive the satellite data and the ancillary meteorological data (Daniel Ziskin, Jarmei Chen); the Level 0-1 processor which calibrates the instrument counts to produce geolocated radiances (Ziskin, Debbie Mao, Chen); and the Level 1-2 processor which comprises a forward model which provides a full simulation of the MOPITT measurement, a cloud detection algorithm, and a retrieval algorithm (David Edwards, Gene Francis, Merritt Deeter, Ben Ho, and Gille). The retrieval combines information from the measurements, the forward model, and previous measurements which define the current understanding of the atmosphere, to obtain the most likely CO profile consistent with the measured MOPITT signal. The Moderate-resolution Imaging Spectroradiometer (MODIS) cloud mask is also used operationally in the current data processing to provide added information about cloud contamination in the MOPITT field of view.

The algorithms continue to be developed. The data for the mission Phase 1, before the instrument cooler failure in April 2001, have been designated as a validated product. The data for the post-April 2001 period, Phase Two, are currently provisionally validated and will be upgraded to fully validated in the near future. Work has continued to characterize the instrument performance in the Phase Two period, and to develop the retrieval algorithms to ensure maximum utilization of the instrument signal to retrieve CO vertical structure.

The algorithms are now being prepared for the next data Version Four. Enhancements will include: (1) a new forward model with improved description of the MOPITT gas correlation cells; (2) an new description of the retrieval a priori surface emissivity; and (3) a variable CO retrieval a priori. The validation of MOPITT retrieved surface skin temperature using collocated MODIS measurements has been a major effort led by Ho. Surface skin temperature information retrieved from MODIS measurements has been used to generate a more accurate global monthly surface a priori emissivity (mean and variance) for use in the MOPITT retrieval algorithm to improve retrievals of surface temperature and CO profile. Monthly 1 degree grid mean 4.7 micron surface emissivity maps have been generated using an iterative algorithm taking as inputs MODIS skin temperature and surface characterization index in combination with MOPITT A-signals, which are most sensitive to the background scene. Analysis of the impact of the new a priori emissivity on the retrievals of tropospheric CO profiles indicates that more vertical information can be obtained, especially at night. This has the effect of reducing the apparent diurnal change in the MOPITT CO retrieval. A manuscript detailing this work is now in preparation, and this will be used in the new Version Four algorithm. The adoption of a new seasonally- and latitudinally-variable CO retrieval a priori (based on both in situ data and current operational MOPITT retrievals) is also planned for version 4. This will hopefully reduce retrieval biases that have been characterized by validation studies. This work is being led by Deeter.

 

MOPITT Data Validation

The on-going activity of validation of the MOPITT CO retrievals (Louisa Emmons) shows the continued accuracy of the data.  In situ measurements from small aircraft, provided by Paul Novelli (NOAA CMDL), continue to form the basis for the validation comparisons.  Figure 8 shows the high correlation between MOPITT retrievals and the in situ data (transformed with the MOPITT averaging kernels) for the Phase Two data through 2003. 

 

Figure 8: Validation of MOPITT CO retrievals for August 2001 to December 2003. Correlations of MOPITT CO with aircraft in situ data are shown for each retrieval level and the total column.  Aircraft CO profiles, provided by Paul Novelli (NOAA CMDL) for five sites, have been transformed with the MOPITT averaging kernels.

The vertical resolution of the MOPITT CO retrievals is a key indicator of retrieval performance and is of interest to many end users. However, vertical resolution is highly variable, and depends on retrieval configuration, surface temperature and emissivity, atmospheric temperature profile, etc. One index for quantifying vertical resolution is termed Degrees of Freedom for Signal (DFS).  DFS approximately represents the number of layers in the retrieved profile which are retrieved independently. Analysis of the MOPITT averaging kernels indicates that current MOPITT retrievals contain up to two pieces of information corresponding to the mid- and upper-troposphere. Figure 9 shows the latitude dependence of the zonal-mean DFS for both daytime and nighttime retrievals, and for both Phase One and Phase 2 periods. Most importantly, the figure shows that retrieval information content decreased only marginally as a result of the loss of half of the MOPITT channels in 2001. This work was recently published in Geophysical Research Letters.

Figure 9: Latitude dependence of the zonal-mean DFS for both daytime and nighttime retrievals, and for both Phase One and Phase 2 periods.

Studies were completed using the 2001 flight data taken by the MOPITT Algorithm Test Radiometer (MATR) aircraft instrument (Alan Hills, Janguo Nui, Deeter) for (1) during April and May over the Oklahoma Cloud and Radiation Testbed (CART) site, and (2) during November over three western U.S. cities (Los Angeles, Las Vegas, and Denver).  These flights were supported with in situ measurements by Paul Novelli (NOAA CMDL). MATR measurements over the western cities show plumes of CO, the direction and distribution of which appear to agree well with the prevailing meteorology. This work has recently been published in Applied Optics.

 

MOPITT Education and Outreach

The MOPITT website continues to be developed. This is regarded as an important means of community outreach and education. The website currently includes details of how to obtain the data and how to use it correctly, along with other MOPITT references.

The MOPITT team makes regular story contributions to the NASA Earth Observatory website. These often highlight intense burning events around the world that are of general interest. The team was also involved in the production of an animation of MOPITT data with accompanying story that was produced by the American Museum of Natural History for distribution as an educational tool. 

 

MOPITT Science Studies

MOPITT Participation in INTEX-A

Remote sensing of CO directly addresses many of the scientific questions motivating aircraft field campaigns, and measurement of this gas is usually rated as being mission critical. CO is an important trace gas in tropospheric chemistry due to its role in determining the atmospheric oxidizing capacity, as an ozone precursor, and as an indicator and tracer of both natural and anthropogenic pollution arising from incomplete combustion. The satellite perspective provides the more general temporal and spatial context to the aircraft and ground-based measurements. During the summer 2004 NASA ICARTT/INTEX campaign, MOPITT CO retrievals were provided in near-real-time using an expedited data processing stream (managed by Ziskin, Chen, and Mao) for use in field analysis and flight planning (Edwards, Emmons and Gabrielle Pfister). Maps of the data were created and posted on the MOPITT website, and Emmons and Pfister were in the field to present and discuss the MOPITT data during daily planning meetings. The large wildfires in Alaska during the summer of 2004 had a strong impact on the CO concentrations in the Midwest and eastern U.S. at times, and the MOPITT data were valuable for tracking the high CO values.  This is shown in Figure 10.

Figure 10: MOPITT 700 hPa CO mixing ratio for the period 15-23 July, 2004, showing the plumes produced by fires in Alaska. The emissions from these fires can be traced across North America and The Atlantic Ocean.

 

INTEX-A also provided MOPITT validation opportunities with in situ CO measurements on the DC-8 from G. Sachse, NASA Langley. Edwards was also Co-Investigator on the French component (ITOP) of the overall ICARTT mission, and on-going collaboration with Jean-Luc Attie at the Laboratoire d'Aerologie in Toulouse, France, resulted in a near-real time assimilation of the MOPITT data into the MOCAGE model for forecasting air quality in the area of flight operations. Measurements taken during the ICARTT campaign are now the subject of several scientific investigations into North American air quality modeling and inverse modeling to improve source emission estimates.

 

Long-range Transport of CO Emissions from Russian Fires

Studying satellite data on global air pollution levels, Edwards and other MOPITT team members at NCAR and other institutions noticed an unusual spike in CO levels in late 2002 and early 2003 that affected the entire Northern Hemisphere. Analysis pointed to Russian source: massive peat fires smoldered near Moscow in the late summer and fall of 2002, and unusually intense Siberian wildfires broke out in the spring and summer of 2003. During the peat fires, Russian colleagues working with spectrometer data from the Obukhov Institute of Atmospheric Physics in Moscow (Leonid Yurganov and Evgeny I. Grechko) took air quality measurements from Moscow and a nearby site at Zvenigorod. The research combined the ground-based measurements with observations of atmospheric pollutants from two instruments on the Terra satellite: CO levels from MOPITT, and aerosol optical depth from MODIS. The results showed that smoke and pollutants from the fires had been carried over much of the Northern Hemisphere, affecting CO levels as far away as North America.

Edwards and colleagues also looked at the impact of emissions from Siberia and other parts of eastern Russia. Massive fires in the giant boreal forests and on the tundra, often started by farmers, typically rage throughout the spring and summer. The 2003 fire season was particularly intense. Satellite data showed plumes from Asia following the jet stream, with high levels of CO crossing the Pacific Ocean, reaching western Canada, and traveling down to the U.S. East Coast—evidence of the global impacts of large-scale fires (Figure 11). The research will be published in the JGR. 

Figure 11: In the spring of 2003, the MODIS instrument on the Terra satellite instrument detected a large number of fires in Siberia, especially in the Baikal region (top). These fires produced large amounts of fine carbon aerosol, also detected by MODIS, that spread over the Pacific Ocean but lasted only a few days (center). They also produced CO, which was detected by the MOPITT (bottom). CO can last over a month, which allowed it to cross the Pacific Ocean and reduce air quality over North America before continuing on around the globe.

  

The CO Budget over Europe

Pfister completed a study on the CO budget for Europe. For this work, CO retrieved from MOPITT was used in conjunction with ground-based data provided by the Austrian Federal Environment Agency and CMDL and aircraft instruments (data provided by the German Aerospace Center [DLR] and National Center for Scientific Research, Paris [CNRS]), and compared to simulations from the MOZART CTM. The model simulations were provided by Gabrielle Petron (NCAR’s Advanced Study Program [ASP]). The results showed that, on average, the largest contribution to the anthropogenic CO load over Europe at the surface comes from regional sources. Further significant impact is evident from sources in North America and Asia. With increasing altitude the influence of European sources weakens, and the impact of CO from other continents gains in importance with Asian emission showing the highest contributions during most months and at most heights. Studies where the CO was tagged in the model according to the time of emission showed that the transport time needed for pollution from North America to reach Europe might be as short as one week. Asian emissions can be seen in Europe less than two weeks after being emitted when transported towards the northwest. The results of these studies have been published in JGR.

 

Pollution from Mega-Cities

Work has begun to see if the MOPITT instrument could be used to track CO pollution originating from cities (Cathy Clerbaux). Though MOPITT was not optimized to detect pollution plumes from cities due to poor measurement sensitivity in the boundary layer, initial results look promising. By averaging the data over four years to reduce noise from transient plumes, signatures from cities have been distinguished from transported emissions. This pollution from distant sources, clouds and the instrument's low boundary layer sensitivity bias the results. This initial investigation focused on cities such as Mexico City, Kuala Lampur, Singapore, Jakarta and Surabaya, Indonesia. MOPITT shows how El Niño-related wildfires in Kalimantan on Borneo Island in Indonesia, contaminated the air in 2002 above Jakarta and Surabaya. The instrument also shows how pollution gets dispersed from cities. Mexico City and Jakarta are both surrounded by mountains. Due to topography, the satellite reveals that pollution can only escape upward or through openings---to the north for Mexico City and east for Jakarta. This work will provide the basis for future efforts in support of the MIRAGE field campaign in Mexico City.

 

Involvement with Other Satellite Missions

Collaborations are underway with Larrabee Strow and Wallace McMillan (University of Maryland, Baltimore County [UMBC]) who are investigating the potential for retrieving CO from the Aqua/AIRS (Atmospheric Infrared Sounder) instrument. Data are also being made available to the National Institute for Space Research in The Netherlands (Ilse Aben) for use in CO validation studies for the Envisat/SCIAMACHY (SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY) instrument. MOPITT data will also provide key validation of the CO retrievals from the recently launched NASA Aura satellite, carrying the TES (Tropospheric Emission Spectrometer) instrument, and Edwards is the Aura Validation Team Liaison for MOPITT.

 

Seasonal and Inter-Annual CO Variability

Now that there is an almost five-year record of MOPITT data, the seasonal and inter-annual CO variability may be examined. Edwards has led a project to investigate the extent to which seasonal variability is explained by the CO photochemical sink in conjunction with sporadic perturbations caused by wildfires.  Gille and Yudin have also studied interannual variations by using MODIS Fire counts to identify fire sources and have compared with year-to-year CO variations.  Using inverse modeling tools in conjunction with the MOZART CTM and surface network measurements, they estimated the potential inter-annual variations of the biomass burning over North Asia.  This work is being prepared for submission to GRL.

 

Data Assimilation and Inverse Modeling

Work continues on the assimilation of MOPITT retrievals in chemistry transport models and on inverse modeling of CO surface emissions using different schemes and techniques. Two articles on  the inverse modeling of CO surface fluxes  (Petron et al., 2004) and assimilation of  MOPITT CO retrievals with optimized fluxes (Yudin et al., 2004) will be published in the next issues of GRL. Jean-Francoise Lamarque is leading an effort to evaluate biomass burning emission inventories using the assimilation of MOPITT data.

 

Comparison of CO and Aerosol Emissions from Biomass Burning

Edwards is leading a study to investigate emissions from biomass burning in Africa and South America. This is a major source of pollution in the tropical troposphere and a major forcing of tropospheric chemistry. The outflow of both aerosol and CO from the widespread fires in southern Africa and South America during September-November 2000, is being studied using observation from the Terra satellite, CO profiles from MOPITT and aerosol optical depth from MODIS. Recent developments in aerosol retrieval allow the distinction to be made between fine and coarse mode particles. The fine mode particles are produced by the same anthropogenic combustion processes that emit CO, and comparison of the fine mode aerosol and CO distributions provide information about biomass plume aging and the associated advection and convection of the emissions. The long range transport of these pollutants and the impact on atmospheric air quality in remote oceanic regions is also being studied, along with the seasonal changes in the pollutant distributions by comparing with the observations of CO and fine mode aerosol made during the December 2000-February 2001 period. A paper describing this work will soon be submitted to JGR.

  

Photochemistry

Urban areas are strong sources of pollutant gases and aerosols that can influence both regional and global environments.  These pollutants include primary pollutants released into the urban atmosphere (primary pollutants, e.g., hydrocarbons and NOx), as well as secondary pollutants produced in the atmosphere by photochemical processing (secondary pollutants, e.g., ozone, inorganic and organic nitrates, acids, peroxides, carbonyls, and other partly oxidized organics).  Many of these secondary pollutants play an important role in the atmosphere far from source regions, for example as sources of HOx and NOx in the remote atmosphere.  Understanding the details of this photochemical processing is a primary focus of ACD.

 

Peroxy Radical Studies

Chris Cantrell of the ARS Group investigates the behavior of odd hydrogen and organic radical species in the troposphere through observations using state of the art instrumentation.  Over the last few years, the ARS Group has developed a chemical ionization mass spectrometric-based method for the quantification of hydroperoxy and organic peroxy radicals, which has been deployed in several aircraft- and ground-based campaigns.  Work this year involved publication of results from recent studies and further laboratory work to improve the performance of the instrument during field deployments.  Progress was slowed by the fact that Cantrell took a temporary assignment as Associate Program Director for Atmospheric Chemistry at the National Science Foundation in Arlington, Virginia, from August 2003 to August 2004.

In 2001, observations of peroxy radicals were made from the NASA P-3B aircraft during the Transport and Atmospheric Chemistry near the Equator – Pacific (TRACE-P) campaign.  This experiment examined the emissions and evolution of trace gases from eastern Asia.  Funding for participation in the campaign, analysis of the observations, and preparation of a manuscript (Cantrell et al., 2003) were provided by the NASA Tropospheric Chemistry Program.  The paper presents methods for approximating the concentration of free radical species and ratios of species.  A steady state model was employed that satisfactorily reproduces the observed concentrations except during encounters with clouds or air masses with high aerosol surface area densities, and when the NO concentrations were very high (> 0.5 ppbv) or very low (<5 pptv).  The observations provided indirect evidence of the heterogeneous uptake of radicals by cloud droplets and aerosols.  The failure of the model and low and high NO concentrations implies missing or misrepresented processes that will be investigated further.  Cantrell contributed to several other papers related to the TRACE-P campaign.

The TRACE-P campaign involved significant collaboration with scientists from universities and national laboratories.  The members of the Science Team are shown in Table 1.

ARS Table 1: Science Team members for TRACE-P mission. 

 

Bruce E. Anderson

NASA Langley

Eric C. Apel

NCAR

Elliot L. Atlas

NCAR

Melody A. Avery and Stephanie A. Vay

NASA Langley

Alan R. Bandy

Drexel University

Donald R. Blake

University of California – Irvine

Edward V. Browell

NASA Langley

William H. Brune

Pennsylvania State University

Christopher A. Cantrell

NCAR

Gregory R. Carmichael

University of Iowa

Antony D. Clarke

University of Hawaii

James H. Crawford

NASA Langley

Douglas D. Davis

Georgia Institute of Technology

Fred L. Eisele

Georgia Institute of Technology

Johann Feichter

Max-Planke-Institut fur Meteorologie

Frank Flocke

NCAR

Alan Fried

NCAR

Henry E. Fuelberg

Florida State University

Brian G. Heikes

University of Rhode Island

Daniel J. Jacob

Harvard University

Makoto Koike

Nagoya University

Yutaka Kondo

Nagoya University

Reginald E. Newell

MIT

Samuel J. Oltmans

NOAA

Michael J. Prather

University of California – Irvine

Daniel D. Riemer

University of Miami

Glen W. Sachse

NASA Langley

Scott T. Sandholm

Georgia Institute of Technology

Richard E. Shetter

NCAR

Hanwant B. Singh

NASA Ames

Robert W. Talbot

University of New Hampshire

Anne M. Thompson

NASA Goddard

Charles R. Trepte

NASA Langley

Rodney J. Weber

Georgia Institute of Technology

 

In May and June of 2002, a ground-based comparison of the NCAR peroxy radical CIMS instrument (PeRCIMS) and Bill Brune’s (Pennsylvania State University) Ground-based Tropospheric Hydrogen Oxides Sensor (GTHOS) was carried out.  It involved comparing ambient concentrations of HO2 and HO2+RO2 radicals and comparing signals from two synthetic radical sources.  The results were very good and indicated the ability to independently generate known peroxy radical levels (see Figure 12), and the ability to quantify ambient radical levels.  The results were published this report year (Ren et al., 2003).  The outcomes were encouraging enough that a second comparison may take place in the spring or summer of 2005.  This project involved collaboration with NCAR and Pennsylvania State University faculty and staff (see Ren et al. [2003] author list) that led to collection of valuable data and publication of two papers (Ren et al., 2003; Ren et al., 2004).

 

 

 

Figure 12: Comparison of GTHOS measured HO2 with that generated by the NCAR calibrator (top panel), comparison of PeRCIMS measured HO2 with that generated by the Penn State calibrator (middle panel) and comparison of PeRCIMS and GTHOS measurements on the same calibrator, either NCAR (squares) or Penn State (circle) (bottom panel).

 

Two final papers were published this year on the ACD-led TOPSE (Tropospheric Ozone Production about the Spring Equinox) campaign that involved measurements of a number of species aboard the NCAR/NSF C-130 aircraft during the winter to spring seasonal transition in 2000.  These deal with the behavior of reactive nitrogen species (Murphy et al., 2004) (in collaboration with Ronald Cohen and students at the University of California, Berkeley) and photochemical ozone production (Stroud et al., 2004) (in collaboration with internal and external TOPSE participants) and help to complete the interpretation of the TOPSE observations.

One final paper on the ACD-led International Photolysis frequency Measurement and Modeling Intercomparison (IPMMI) exercise was published this year related to the observations and radiative transfer modeling of the UV-B photolysis of ozone, j(O(1D)) (Hofzumahaus et al., 2004).  The IPMMI campaign and subsequent analysis involved collaboration with a number of scientists from the U.S. and Europe, and summarized the ozone photolysis results that solidifies the current understanding of the ozone molecular parameters and ability of the community to accurately measure and model this quantity.

Additional laboratory work on peroxy radicals was done by members of the Laboratory Kinetics Group, Geoff Tyndall and John Orlando, who, in collaboration with Alam Hasson (California State University, Fresno), conducted detailed modeling studies of previously reported laboratory experiments which revealed substantial yields of hydroxyl radicals in the reactions of HO2 with both acetyl peroxy and acetonyl peroxy radicals.  In the former reaction, an OH yield of 40% was found, while in the latter case a yield of 67% was obtained.  Prior to the beginning of this work, no evidence had been reported for the direct production of OH.  Modeling studies indicated that the effects on tropospheric ozone and OH would probably be small (<5%); however, the implications for the stable oxygenated products would be greater.  The reaction of HO2 with acetyl peroxy has previously been thought to produce only acetic and peracetic acids.  The yields of these compounds (and hence their source from this reaction) will now have to be reduced by almost a factor of 2.  If other peroxy radicals from oxygenated species also undergo a similar reaction, the predicted yields of hydroperoxides will be substantially reduced.  (Hasson et al., J. Phys. Chem. A., 2004).

 

Peroxyacyl Nitrates (PANS)

As mentioned above, Flocke and Swanson flew a new instrument, the PAN-CIGAR (PAN-CIMS Instrument by GIT and NCAR), for fast (1-2 sec), continuous measurements of peroxy acetyl nitrate (PAN) and related species on the NOAA P-3B aircraft as part of the NOAA-led ICARTT and NEAQS programs.

The instrument was flown during ICARTT missions without an on-board operator and produced better than 85% data coverage for the entire mission.  PAN, PPN, MPAN, APAN, PiBN, PBzN and MethoxyPAN were measured simultaneously.  The performance is demonstrated in Figure 13, which shows some results from the July 20 flight while near 1 km altitude and while crossing the polluted outflow from New York City at a downwind distance of about 120 km. 

Figure 13: Preliminary data from the 7/20/2004 flight through the NY City Plume, ~120 km downwind, ~1 km altitude, during the ICARTT program. 

 

While this outflow event shows a large amount of structure, probably caused by air masses of different photochemical age and different initial pollution levels, an excellent correlation down to the fine time scale of seconds is observed between ozone and PAN as a result of photochemical activity.  These PAN data are the first reliable high-time resolution (2 sec) continuous measurements made from an aircraft.  Similar transects of biomass burning plumes encountered during ICARTT will allow unprecedented analysis of the partitioning of reactive nitrogen species in aged plumes.  The accuracy of the instrument could be verified through comparison with other measurements of reactive nitrogen and the sum of all reactive nitrogen on board the NOAA P-3 aircraft, and comparisons with instruments on-board the NASA DC-8, that also flew in conjunction with some of the ICARTT missions.  Two abstracts analyzing results from the flights have been submitted for the AGU Fall Meeting. 

ICARTT/NEAQS was an international multi-aircraft, ship and ground-based program including instrumented aircraft from England and Germany.  Principal collaborators with the PAN Group were James Roberts, Andy Neuman, John Nowak, and Fred Fehsenfeld, all of the NOAA Aeronomy Laboratory.

 

Formaldehyde (CH2O)

The APOL Group (Alan Fried, Jim Walega, and Dirk Richter) has been actively involved in efforts to advance understanding of tropospheric photochemistry based upon high quality ambient CH2O measurements acquired during various field campaigns. Last year’s ASR describes one aspect of this activity involving the APOL Group’s TRACE-P data. The Group is continuing with this endeavor this year with INTEX-NA data. Although it is far too early to formulate a comprehensive story, a preliminary first look at this data reveals a very important finding: namely, the persistence of elevated CH2O mixing ratios at high altitudes during the summer time over the continental United States. Persistent continental thunderstorm activity during the summer months vertically convects polluted boundary layer air to high altitudes where it eventually mixes with cleaner background air in the outflow of clouds. Although this process has been well established, vertical convection of soluble and reactive gases, like CH2O, has not been well characterized during such events. The flight tracks during the INTEX-NA study, which passed over natural and anthropogenic source regions of the south and mid-west United States, provided an excellent opportunity to study cloud outflow and cloud processing events.

The histogram plot of Figure 14 displays the APOL Group’s one-minute CH2O measurement distributions acquired during four early flights in July on NASA’s DC-8 aircraft during the INTEX-NA campaign. These measurements were all acquired at pressure altitudes > 30,000 feet where one typically expects to observe CH2O mixing ratios around 50 to 100 pptv. Although the observed spread is fairly large, the median value of 192 pptv is more than a factor of 2 higher than typical expected background levels. Such elevated CH2O levels in the upper troposphere can play a significant role in the HOx radical budget since the primary source of these radicals, O1(D) + H2O, decreases as the available H2O vapor decreases with altitude. Despite the fact that this observation is based on very limited data, the Group observed a similar persistence of elevated CH2O at high altitudes during many other flights.

 

Figure 14: Histogram of the CH2O distribution observed Palt > 30 kft during four selected INTEX-NA flights in early July 2004.

 

Radiation

Photochemical reactions provide the driving force for much of the chemistry in the atmosphere.  The in situ rates of these photolysis reactions are important in understanding production and loss terms for the key atmospheric species odd hydrogen radicals and ozone.  The objective of this research by the ARIM Group (Rick Shetter, Barry Lefer, and Sam Hall) was to deploy two SAFS systems on the NASA DC-8 aircraft platform during the INTEX-A mission in the summer of 2004 to measure the in situ total spectral actinic flux as a function of wavelength and calculate the in situ photolysis frequencies of 23 important photochemical reactions.  Photolysis frequencies for photodissociation reactions involving O3, NO2, CH2O, HONO, HNO3, N2O5, HO2NO2, PAN, H2O2, CH3OOH, CH3ONO2, CH3CH2ONO2, CH3COCH3 , CH3CHO, CH3CH2CHO, CHOCHO, CH3COCHO, CH3CH2CH2CHO, and CH3COCH2CH3 will be calculated from the measured UV-VIS spectral actinic flux. The instrumentation, which has flown on the NASA DC-8 during the Pacific Exploratory Measurements (PEM)-Tropics A , Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX), PEM-Tropics B, Stratospheric Ozone Loss Validation Experiment (SOLVE), and the TRACE P missions, had an approximated detection limit of less than 0.01 W/m2/nm dependent on wavelength resulting in photolysis frequency detection limits of 2 X 10-7 sec-1 for jO(1D) and 1 X 10-7 sec-1 for jNO2, all with a time response of 10 seconds.

In addition, the ARIM Group deployed a newly developed actinic flux system equipped with a monolithic monochromator with a cooled back thinned windowless CCD detector and a PC014+ based data acquisition and control system. This new system will have a time response of 0.1 to 10 HZ.

The instruments performed quite well on all of the aircraft flights with 100% data return. Final calibrations are currently being performed and data will be submitted to the INTEX/ICARTT archive in the next few months for use by the INTEX and ICARTT science team members.

 

Regional and Global Chemical Transport Models and Air Pollution Studies

Many of the chemical and physical processes that occur in the atmosphere are non-linear, so it is not possible to apply simple scaling relationships (e.g., simple dilution) to estimate the impacts on chemistry and climate of current emissions and future urban growth.  Therefore, detailed numerical model representations of the primary chemical and physical processes are required.

 

Weather Research Forecasting with Chemistry (WRF-Chem)

ACD scientists are playing a major role in the development and testing of a new, state-of-the-art regional chemistry transport model, the Weather Research Forecasting with Chemistry (WRF-Chem) model.  Xuexi Tie, Sasha Madronich, and visiting graduate students, Zhuming Ying (York University) and GuoHui Li (Texas A&M University [TAMU]), are collaborating with George Grell of NOAA’s Forecast Systems Laboratory (FSL) to implement chemical models developed at NCAR into WRF-Chem and to apply the model to the planning of a major international field campaign, MIRAGE-Mex, planned for early 2006.

The WRF-Chem model was successfully ported over the central Mexico region, with emissions data for Mexico City and the surrounding region and was used to perform simulations at various resolutions (4 km, 6 km, and 12 km).  Mexico City emissions were implemented through a collaboration with Aron Jazcilievich of the Universidad Nacional Autonoma de Mexico (UNAM).  Preliminary results show that the modeled temperatures and winds reproduce well the observed diurnal cycles, but with a cold bias indicating that the “heat island” of the city is not yet well represented by the model.  The diurnal cycles and magnitudes of surface concentrations of CO, NOx (NO +NO2), and O3 within Mexico City compare well with observations, and show that the model is able to capture high pollution events.  In anticipation of the MIRAGE-Mex field campaign, the interaction of urban outflow plume with the surrounding region was studied.  For this study, Alex Guenther and Christine Wiedinmyer provided current estimates of regional biogenic (vegetative) emissions, and Jean-Francois Lamarque provided biomass burning emissions.  Preliminary results show (Figure 15) that this interaction leads to more regional O3 production than would be expected from the three sources (urban, biogenic, and biomass burning) taken in isolation.  These preliminary results have been presented at conferences (Tie, and Madronich, Modeling of Mexico City Air Pollution and Outflow with WRF-Chem, 5th WRF/14th MM5 User’s Workshop, June 22-25, 2004, Boulder, CO; Tie, Madronich, Effect of mobile, biomass burning, and biogenic emission on Mexico City’s Air Pollution and Outflow, 13th International Scientific Symposium of Transport and Air Pollution, Boulder, September 13-15, 2004, Boulder, CO.) 

Figure 15: Ozone (O3) concentrations simulated with the WRF-Chem model, showing the interaction between the Mexico City pollution plume with regional biomass burning and biogenic emissions. Upper panel shows the O3 resulting from urban emission only. Middle panel includes effects adding biomass burning emissions, which contribute NOx in the NOx-limited regime (far-field, ca. 200-300 km).  Lower panel adds biogenic emissions, which contribute hydrocarbons in the hydrocarbons-limited regime (near-field, 50-150 km).

 

The WRF-Chem model is also being used to determine the most favorable location for ground-based measurements during MIRAGE-Mex.  This heavily instrumented “supersite” will be a link between the urban measurements and the mostly aircraft-based, regional-scale measurements, and therefore should be located outside the city in the direction of prevailing outflow.  Initial WRF-Chem simulations for late February 2004 indicate that the outflow was predominantly towards the north-east (Figure 16), but additional simulations are underway to better establish the frequency distributions.  This information, together with logistic considerations, will be used to select the location of the measurement site.


Figure 16: Surface concentrations of CO and NO2 near Mexico City during 27-29 Feb 2004.  Note prevailing outflow towards the North-East.

 

HANK Regional Transport Model

As the development and testing of the WRF-Chem model continues, some regional studies have been carried out with ACD’s more mature HANK model. HANK is an off-line regional model based on MM5 meteorology and is in use by the broader community.  A collaborative study by Peter Hess, Tie, and Wenfang Lei (TAMU) examined the air quality in the Houston-Galveston area, and, in particular, the role of industrial emissions, with two publications describing the results (Lei et al., J. Geophys. Res., 2004; Zhang et al., Proc. Natl. Acad. Sci., 2004). The HANK model was also used by Hess and collaborators, Moti L. Mital (Ohio Supercomputing Center) and C. Sharman, (National Physical Laboratory, New Delhi, India) on first-ever regional air quality simulations in India, where pollutant concentrations are exceptionally high and therefore of regional and even global interest.

 

Global Chemical Transport Models and Air Pollution Studies

The MOZART-2 model, developed by ACD scientists in collaboration with researchers from universities and other institutions, has been used to elucidate a variety of global-scale issues. Hess, in collaboration with David Parrish (NOAA/Aeronomy Laboratory) used MOZART-2 to examine decadal trends of pollutants on the west coast of the U.S. between 1985 (measurements made at Punta Arenas) and 2002 (measurements made during the ITCT-2K2 experiment). The model results suggest that much of the measured differences during these two time periods are due to the sampling of different meteorological regimes, rather than pollution trends. A paper describing this work has been accepted.

Hess and post-doctoral fellow, Kazuyo Murazaki, used MOZART-2 to examine for the first time the effect of climate change on U.S. air quality, by comparing simulations for 1990-2000 and 2090-2100. The main conclusion is that while climate change increases the local ozone production over the eastern U.S, it decreases the import of ozone from Asia. Significant changes were also found in photolysis rates over the U.S. as well as in chemical inflow, outflow, and transport. Overall, these results suggest that climate change and air quality will be fundamentally linked over the next century.

Tie, Madronich, and collaborators, Daniel Lack, Neville Bofinger, Aaron Wiegand  (Queensland University of Technology) and Bernard Aumont (University of Paris) implemented a parameterization for the formation of secondary organic aerosols (SOA) in MOZART-2, and carried out simulations to assess the effect of the SOA on global atmospheric oxidants. These results (Lack et al., 2004.) are part of a wider assessment of the role of aerosols in global tropospheric chemistry (Tie et al., in preparation).

The MOZART-2 model was also used by Tie, Guenther, and Wiedinmyer to examine how regional and global tropospheric chemistry might be affected by changes in biogenic volatile organic emissions that occur as a result of land cover change.  Tie, with collaborators Renyi Zhang and David Bond (TAMU) examined the relative impacts of anthropogenic and natural NOx sources over the U.S., and with collaborators Sushil Chandra and Jerrold R. Ziemke (NASA) found evidence for elevated tropospheric O3 over the oceans in the Northern Hemisphere. (Zhang et al., Proceedings of National Academic Science, 2003; Wiedinmyer et al., submitted 2004; and Chandra et al., submitted 2004.)

Louisa Emmons, Hess, and Lamarque, in collaboration with John Mak (State University of New York [SUNY], Stony Brook), have been studying the signatures of 13C in CO using observations and model simulations (Figure 17).  Since different sources of CO have different isotope ratios, 13CO will vary depending on the relative contributions of the sources.  Tracers of the 13C isotopes of all of the carbon compounds have been added to the MOZART mechanism.  Using the biomass burning emissions developed by James Randerson (University of California, Irvine), that include the C3/C4 plant type fraction, they have been able to include the appropriate 13C emissions for forest versus savanna burning.  The model simulation of 13CO has helped explain the observed seasonal and interannual variations in the time series at several stations.   The differences between modeled and measured amounts of both CO and the isotope fraction are being used to estimate improvements to the CO emission inventories. 

Figure 17: Comparison of measurements and MOZART results for CO and d13CO at Barbados (13N, 59W) for 1997 through 1999.  The top  panel shows CO measurements from J. Mak, SUNY Stony Brook (blue dots) and the NOAA/CMDL network (black stars), along with the simulated CO.  The various source contributions to CO (CH4 and NMHC oxidation, and fossil fuel, biofuel, biomass burning, biogenic and ocean emissions) are also shown.  The second panel shows measured and modeled d13CO.  The third panel shows the CO source contributions as fraction of the total CO (in %).

 

Research Groups

Analytical Photonics and Optoelectronics Laboratory (APOL)

Atmospheric Odd Nitrogen (AON)

Atmospheric Radiation Investigation and Measurement (ARIM)

Biosphere-Atmosphere Interactions (BAI)

Laboratory Kinetics (LK)

Measurement of Pollution in the Troposphere (MOPITT)

Measurements, Standards, and Intercomparisons (MSI)

Regional and Process Studies (RPS)

Stratospheric/Tropospheric Measurements (STM)

 

 

Reactive Carbon Research

One of the major challenges in tropospheric chemistry over the next decade will be to understand and predict the fate of reactive carbon.  Achieving this goal requires the study of the many complex chemical, physical, and biological processes that control the surface emissions of these species, their chemical transformations in the atmosphere (in both gas and condensed phases), and their eventual removal from the atmosphere via deposition.  A number of activities in ACD, including field and laboratory observations, focused on the study of reactive carbon over the past year.

 

Emissions of Primary Organic Compounds

This year the Eric Apel of the MSI Group collaborated with university and government researchers on a number of important data interpretation projects resulting in two publications.

In Grossenbacher et al., 2004, two data sets are compared in which isoprene nitrate concentrations are measured along with (among others) isoprene, NOx, and first generation reaction products with isoprene: methacrolein and methyl vinyl ketone.  A conclusion of the study is that it is important that isoprene nitrates be quantified as part of future atmospheric field studies, along with other biogenic nitrates, to assess biogenic organic nitrates’ relative role in sequestering atmospheric NOx, and the extent to which the biogenic organic nitrates represent a significant fraction of the alkyl nitrates detected in previous studies.  This is particularly important in light of suggestions that atmospheric deposition of nitrogen may be an important source of nitrogen to nitrogen-limited forests, and that gas-phase nitrogen compounds can undergo direct uptake by leaves, thus potentially impacting the carbon cycle.

Jobson et al., in press, discusses that Houston, Texas, has one of the worst air pollution problems in the country.  The 2000 TEXAQS was initiated to help ascertain the causes of the poor air quality.  The MSI Group’s instrument was one of four in situ instruments making measurements of C1-C10 hydrocarbons at the La Porte supersite during the TEXAQS Experiment.  This paper explores the sources of VOCs in the Houston area and finds that industrial emissions have a strong impact on the atmospheric mixing ratios of light alkanes and light alkenes; the light alkenes at times dominated the airmass reactivity.  These species react very quickly and in the presence of NOx can rapidly form ozone, one of the major components of poor air quality.  

 

Reactive Carbon Species as Sources and Reservoirs of Radical Species

Eric Apel of the MSI Group has also collaborated with university and government researchers on studies of hydrocarbons as sources of radical species.

Measurements of the Penn State Total OH Loss Measurement (TOHLM) instrument (DiCarlo et al., 2004) with OH losses calculated from the sum of the measurements of individual species thought to be the largest contributors to OH loss in the forested environment. A major discrepancy was found which leads to the conclusion that there are unmeasured (unknown) reactive species in the forested environment that are the cause. Potential candidate reactive species are the C15 sesquiterpenes. It is suggested that significant work remains in order to understand the chemical environment in the forest.

Oxygenated Volatile Organic Carbon (OVOC) contribution to the HOx cycle

There is much uncertainty in our understanding of regional and global distributions of oxygenated VOCs (OVOCs), their contribution to the HOx cycle and to secondary organic aerosol formation (Apel et al., in preparation). If recent measurements are accurate, there is a suggestion that the OVOCs may in fact be more abundant than non-methane hydrocarbons (NMHCs) (Singh et al., 2004).  Recent experiments have begun to show a convergence between formaldehyde measurements and model results (Fried et al., 2003). However, this is not the case with higher molecular weight carbonyl compounds (Singh et al., 2004); most measurements in the free troposphere for the higher aldehydes (C2 and up) show significantly higher mixing ratios than models predict. This paper in progress explores the distribution of acetone, methanol, acetaldehyde and methyl ethyl ketone in the Pacific during springtime. Relationships to tracer species such as CO, acetonitrile and methyl chloride are investigated with respect to source relationships. The Model for Ozone and Related chemical Tracers (MOZART) model is used to calculate expected mixing ratios and arithmetic ratios of species of interest in the TRACE-P regime and these are compared with measurements.

 

Gas-aerosol Partitioning of Organic Species

Jim Smith and Fred Eisele of the Photochemical Oxidation and Products Group (POP) have developed an instrument, the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS), for characterizing organic compounds in ultrafine aerosol.  Historically, the identification of organic compounds has been one of the most difficult challenges in aerosol measurement, as organic compounds in aerosol (1) have very low vapor pressures and are not easily detected, (2) are usually large compounds and easily decompose during analysis, and (3) often have many structural isomers, and are thus difficult to identify.  The TDCIMS technique, which has undergone several improvements over the past year, is well suited for overcoming many of these challenges.  Since it relies on chemical ionization mass spectrometry to ionize and detect compounds in the aerosol, it is both sensitive and imparts less fragmentation to the parent ion compared to techniques that rely on electron impact ionization or laser ablation and ionization.  An additional feature is its use of a triple quadrupole mass spectrometer, which allows for the identification of complex ions and structural isomers by collision-induced dissociation of ions of a pre-selected mass.  In addition to these inherent advantages, a number of additional improvements have been incorporated in the TDCIMS instrument specifically targeted at organics.  New data acquisition and control software now allows for rapid mass spectrum acquisition of up to 50 amu s-1, thus allowing large mass ranges to be scanned in the time that the aerosol is undergoing thermal desorption.  Temperature programming has also been added to the thermal desorption procedure allowing this to be ramped from room temperature to ~300 °C.  An octopole ion guide has also been installed in the ion beam path, resulting in improvements in sensitivity of up to an order in magnitude.  Evaluation and calibration of the instrument is on-going, as are measurements of ambient aerosol performed outside the POP laboratory and at the Marshall Test Site.  This work is being carried out by a second graduate student, also supported by the ASP graduate fellowship program and co-advised by J. Smith (ACD) and Jose Jimenez (CU).

 

Laboratory Kinetics

The Laboratory Kinetics (LK) Group (Geoffrey Tyndall, John Orlando, and David Hanson) has continued its studies of tropospheric oxidation processes, maintaining an emphasis on the chemistry of volatile organic compounds.

 

Oxidation Pathways for Alkyl Iodides

Alkyl iodides (e.g., ethyl iodide, CH3CH2I) are emitted from the oceans to the atmosphere. Once in the marine boundary layer these compounds are rapidly oxidized by photolysis and by reaction with OH and chlorine atoms, leading to the release of free iodine atoms.  The subsequent chemistry of these iodine atoms is believed to result in the destruction of ozone and the formation of new particles in the boundary layer.  The LK Group, along with colleagues from the GIT and Auburn University, has been collaborating on a study of the mechanism of the oxidation of these alkyl iodides.  The reactions of ethyl iodide and 2-propyl iodide with chlorine atoms have been shown by both experimental and theoretical means to proceed in part via the formation of a bound complex and in part via more conventional hydrogen abstraction pathways.  Figure 18 shows product yields from the oxidation of 2-propyl iodide. The propene and chloroacetone are formed following elimination of iodine from the initially formed primary alkyl radical, while acetone comes from the secondary oxy radical.  The 2-chloropropane is produced from an exchange reaction via the adduct.  Product yield data are in qualitative disagreement with a previous study, but are in keeping with expectations based on this Group’s previous studies of the analogous bromine compounds and with general halocarbon oxidation structure/reactivity rules.

 

Figure 18:  Products observed in the Cl-atom initiated oxidation of 2-iodopropane, for [CH3CHICH3]o = 14 x 1014 molecule cm-3, in 720 Torr air diluent:  Acetone, solid circles and solid line (upper); propene, open circles and solid curve (upper); 2-chloropropane, open squares and solid line (lower); chloroacetone, solid squares and solid line (lower).

 

Nitrate Production from Toluene Oxidation

The rate-limiting step in the tropospheric production of ozone is the reaction of peroxy radicals (HO2 and organic peroxy radicals, designated RO2) with NO:

RO2 + NO ® RO + NO2

In competition with this radical cycling pathway is the formation of organic nitrates,

RO2 + NO + M ® RONO2 + M

a process that removes reactive radicals from the atmosphere and limits the extent of ozone production.  There is currently a great deal of activity centered on achieving a quantitative understanding of organic nitrate production over the range of temperature and pressure conditions encountered in the troposphere.  Working with scientists at NCAR and at the Ford Motor Company, Cherelle Blazer (SOARS) has been examining the extent of nitrate production from the oxidation of toluene, a major anthropogenic emission.  Chlorine atoms are reacted with toluene in an environmental chamber to provide a clean source of benzyl peroxy radicals in the presence of NO, and the yield of benzyl nitrate is then quantified as a function of temperature and pressure.  The data indicate a strong positive dependence of the yield of benzyl nitrate on pressure as expected.  However, preliminary indications suggest that the nitrate yield does not increase significantly with decreasing temperature.  This latter result conflicts with current understanding, and may lead to substantial changes in predicted nitrate formation rates in the troposphere.

 

Oxidation Mechanisms of Methyl Formate and Methyl Acetate

Methyl formate and methyl acetate are important members of the ester family, oxygenated organic molecules that are present in the atmosphere. While both may be emitted from vegetation, their major sources are thought to be from their use as solvents and flavoring agents in the food industry. They can also be produced directly in the atmosphere from the oxidation of ethers. While esters are undoubtedly present in urban atmospheres, their measurement has proven difficult. ACD scientists and post-doc Andre Pimentel (NASA Goddard) have studied the oxidation of both these esters by OH radicals, their primary mode of destruction in the atmosphere.

            OH + CH3C(O)OCH3 ® H2O + CH3C(O)OCH2                 (1a)

            OH + CH3C(O)OCH3 ® H2O + CH2C(O)OCH3                 (1b)

k1 = 3.5x10-13 cm3 molecule-1 s-1

            OH + HC(O)OCH3 ® HC(O)OCH2                         (2a)

            OH + HC(O)OCH3 ® C(O)OCH3                                        (2b)

k2 = 1.8x10-13 cm3 molecule-1 s-1

 

Both reactions are very slow, which makes quantification of the product yields difficult. However, theoretical prediction of the branching ratios is also difficult for slow reactions, making measurement essential. Detailed studies of both molecules revealed evidence for OH attack at both carbon atoms in each molecule. Pathways (1a) and (2a) both lead to the formation of organic acids and anhydrides (which will probably be taken up by droplets and hydrolyzed to the corresponding acids). Pathways (1b) and (2b), on the other hand, produce simpler products such as CO and CO2. Figure 19 shows formation of acetic acid, acetic formic anhydride, and CO2 from the oxidation of methyl acetate by OH radicals. The CO2 yield is curved upwards, indicating that it is formed from the rapid decomposition of another product.

 

Figure 19: Product yields from the reaction of OH with methyl acetate (MeAc) at 700 Torr total pressure in the presence of 300 Torr O2. The data for CO2 have been offset vertically by 0.3 mTorr, and the line through the CO2 data is a quadratic fit, for visual purposes. The data clearly indicate OH attack at both possible sites in the molecule.

 

In a separate set of experiments, chlorine atoms were used to oxidize methyl acetate at a variety of temperatures. The resulting oxy radical, CH3C(O)CH2O∙ can either react with O2, forming formic acetic anhydride (AFAN), or decompose by the so-called alpha-ester rearrangement to give acetic acid and the formyl radical.

            CH3C(O)OCH2O® CH3C(O)OH + HCO

The latter step is temperature dependent, and so a strong variation of the product yields with both oxygen and temperature is anticipated. Figure 20 shows the yields of AFAN and acetic acid from the combined set of experiments.  The lines represent a global fit to all the data using an activation energy of 10.1±1.5 kcal/mole. The ester rearrangement is a reaction unique to oxy radicals derived from esters, involving a five-membered Hydrogen atom transfer to the carbonyl group, and this is the first measurement of its activation energy.

The results of both sets of experiments were combined with experiments of the reaction mechanisms initiated using atomic chlorine (Cl) to provide a complete picture of the oxidation of methyl acetate and methyl formate under atmospheric conditions (Tyndall et al., J. Phys. Chem. A., 2004).

Figure 20: Plot of product yields from the oxidation of methyl acetate by chlorine atoms as a function of oxygen pressure at different temperatures. Circles, 253 K; Triangles, 273 K; Squares, 296 K; Diamonds, 324 K. Acetic formic anhydride is given by closed symbols, acetic acid by open ones. The lines are a simultaneous fit to all the data using an activation energy of 10.1 kcal/mole for the alpha-ester rearrangement.

 

Research Groups

Photochemical Oxidation and Products (POP)

Atmospheric Radical Studies (ARS)

Analytical Photonics and Optoelectronics Laboratory (APOL)

Laboratory Kinetics (LK)

Measurement, Standards, and Intercomparisons (MSI)

 

Multiphase Processes in the Troposphere

Multiphase processes are an important part of atmospheric chemical processes and additional studies are required to quantify the chemical and physical gas- and condensed-phase processes that control the number density, size distribution, chemical composition, and physical and optical properties of aerosols.  ACD scientists are addressing these needs through instrument development and field campaigns.

Interactions of clouds, aerosols, and chemistry are complex and varied.  Cloud effects on chemical species include modification of the radiative properties, which directly influence photochemistry and emissions of biogenic organic compounds.  Cloud chemistry, which includes aqueous and/or ice chemistry and modified gas chemistry, affects photochemistry and aerosol composition.

ACD scientists are using cloud-chemistry modeling to evaluate the impact of boundary layer processes and convective transport on chemical species distributions and interactions.

Recent advances in atmospheric chemistry research have focused on the central role of photochemical processing within snow pack.  ACD scientists participated in several field campaigns to evaluate these photochemical processes in mid latitudes and Polar regions.

 

Aerosols

Jim Smith, Lee Mauldin, Ed Kosciuch, and Fred Eisele of the POP Group conducted field measurements of atmospheric ion clusters and testing of a linear ion trap.  If ion inducted nucleation is to play a role in the formation of new atmospheric particles, certain ion clusters such as (H2SO4) n would be expected to be present in the atmosphere at concentrations on the order of 101 to 102 ions cm-3.  Measurements of these clusters is difficult because of their low concentrations, but by using techniques developed in the early 1980s along with some recent improvements, these ions were observed and studied this past summer at the NCAR Marshall field site.  The results are still being analyzed but appear to be supportive of an ion-inducted nucleation model recently developed by the NOAA Aeronomy Laboratory.

Linear ion traps offer several advantages over conventional mass spectrometers for the rapid measurement of large numbers of organics. As is the case for conventional ion traps, linear traps provide near simultaneous measurements of multiple compounds by acquiring spectra in a quasi-parallel manner by trapping and storing a wide range of ion masses and then analyzing them in a time short compared to their collection.  The overall trapping and analysis efficiency of a standard ion trap, however, is quite low while linear traps offers both high ion throughput and high trapping efficiency. Last year a quadrupole mass spectrometer was converted into a linear ion trap mass spectrometer and tested in the laboratory. This year the linear ion trap was interfaced with an ion source capable of atmospheric sampling and taken into the field. The instrument is presently beginning some preliminary measurements at the NCAR Marshall field site.

The POP Group has also designed and built new aerosol instruments and improvements have also been made to the TDCIMS.  The first new instrument is a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA).  The HTDMA exposes size-selected particles to high humidity to characterize their ability to take in water vapor (their hygroscopicity).  The motivation of this research is to understand the relationship between aerosol composition, hygroscopicity and cloud condensation nucleus potential of carbonaceous aerosol.  It is often assumed that based on the hygroscopic growth of an aerosol one can extrapolate and determine the Cloud Condensation Nuclei (CCN) activity of the aerosol.  This may not always be possible, particularly for ambient multi-component aerosols.  An organic species may have a very low hygroscopicity (which would yield low hygroscopic growth at sub-saturated conditions), but still act efficiently as a CCN.  The POP Group’s research will investigate the conditions for which hygroscopicity can be correlated with CCN activity.  With these results, scientists may then be able to formulate an analytic relationship between hygroscopic growth and CCN activation for use in climate models.  This work is carried out in collaboration with Jim Smith and Athanasios Nenes (GIT).  A graduate student from GIT, advised by J. Smith and Nenes, is carrying out this work in the POP laboratory with support from the Advanced Study Program’s Graduate Research Fellowship program.

Another set of instruments, called Radial Scanning Mobility Particle Sizers (RSMPS), were built to perform field measurements of particle size distributions in the diameter range from 3-100 nm.  This work was performed, in part, by Damian Mattis (SOARS).  These instruments are compact and rugged, allowing them to be deployed to remote locations to perform continuous measurements of particle size.  Such surveys will provide a better understanding of the location, meteorology, and chemical environment in which new particle formation and subsequent growth take place.  In some cases these measurements will provide crucial information to allow TDCIMS measurements at a later time.

David Hanson of the Laboratory Kinetics Group (LK) measured the uptake of methane sulfonic acid by dilute sulfuric acid droplets in the laboratory using an aerosol laminar flow reactor (ALFR). This is important for understanding the growth rates of atmospheric aerosols when significant levels of methane sulfonic acid are present. Results indicate that uptake of methane sulfonic acid is very efficient. The results and this conclusion were presented as an invited talk at the 2004 fall meeting of the American Chemical Society. These results are not in agreement with those from a different technique: the droplet train apparatus (DTA) that is in use in several laboratories. Application of these laboratory results to the atmosphere lead to vastly different predictions of particle growth rates which can affect climate processes. Thus it is important to understand the reasons for this descrepancy. Hanson and colleagues seek to understand all the kinetic processes in both the DTA and the ALFR to provide a physically based accounting of them. In this vein, two papers were published in the past year, and another is in preparation, on the physical basis of the emperical relationships that currently support the analysis of the DTA results. These publications are the result of collaborations with Akihiro Morita, Inst. of Molecular Science, Okazaki, Japan, and Masakazu Sugiyama, Dept. of Elect. Eng., Univ. of Tokoy, Japan.

 

Clouds - Cloud Chemistry Modeling

Effect of Boundary Layer Processes on Chemical Species’ Distributions - Segregation of Chemical Reactants in a Shallow Cumulus Boundary Layer

Shallow cumulus clouds provide locations for aqueous chemical reactions in addition to enhancing transport and mixing and scattering radiation.  Mary Barth (ACD’s Regional and Process Studies [RPS] Group, joint appointment with NCAR’s Mesoscale and Microscale Meteorology [MMM] Division), Si-Wan Kim (MMM visitor, Seoul National University), and Chin-Hoh Moeng (MMM) used the NCAR large-eddy simulation (LES) coupled with gas and aqueous chemistry (over 50 species) to investigate the segregation between hydroxyl radical (OH) and isoprene, species which react to eventually produce ozone.  Knowing the degree of segregation between reactants will help improve regional and global-scale chemistry simulations that assume the reactants are well-mixed; it will also improve interpretation of chemical species measurements in the atmospheric boundary layer.  Results of a simulation with only gas-phase chemistry show that segregation of OH and isoprene reaches 30% in the cloud layer (Figure 21).  Inside the cloud layer, the turbulent flux of isoprene is positive and the vertical gradient of the mean OH concentration is also positive.  This leads to a major sink of the covariance between these species, and hence a larger segregation. When aqueous-phase chemistry is also included, the segregation between the two species reaches 40% in the cloud layer, further indicating the importance of cloud chemistry on the distribution of OH and isoprene.  These LES results will continue to be analyzed to determine which chemical reactions are contributing to the covariance of isoprene and OH.

Figure 21:  Intensity of segregation between isoprene and OH at (a) 1200 LT, (b) 1300 LT, (c) 1400 LT and (d) 1500 LT.  Red lines with aqueous chemistry, blue lines with only gas chemistry.  Gray lines are liquid water content (scaled at top of figure).

 

WRF-AqChem: A Coupled Meteorology and Multi-Phase Chemistry Model - Development and Initial Results of Model

Barth, William Skamarock (MMM), and Kim implemented a simple gas and aqueous-phase chemistry mechanism into the WRF model to begin investigations on the effect of convection on the chemical environment.  Convection plays an important role in transporting pollutants from the surface to the upper troposphere, scavenging soluble species and depositing much of the soluble species to the surface, and converting species chemically in the cloud drops. Simulations of the 10 July 1996 STERAO storm were performed to provide a way to evaluate the modeled chemistry results with observations (Figure 22). Sensitivities of the chemical species distributions to the cloud microphysics representation are currently being investigated.  This WRF-AqChem model will continue to be developed by incorporating the aqueous chemistry modules into the community WRF-Chem model, by incorporating lightning production of NOx and interactions between gas and ice phase species.  Barth and Skamarock also plan to continue collaborations with John Worden and Kevin Bowman (NASA Jet Propulsion Laboratory) to examine the feasibility of using convective-scale cloud chemistry modeling with satellite data retrieval of ozone and carbon monoxide.

Figure 22:  Cross-section of the total (gas + cloud water + rain + ice + snow + hail) mixing ratio of carbon monoxide (CO) and of formaldehyde (CH2O).  Both species are found in high concentration near the surface and lower concentration above the boundary layer. Carbon monoxide, an insoluble species, is primarily transported to the upper troposphere, while CH2O, a soluble and reactive species, has a fraction reacted or precipitated to the ground.

 

Intercomparison of Convective Cloud Chemistry Models

Barth designed and led an intercomparison study for convective cloud chemistry models as part of the 6th International Cloud Modeling Workshop, Cloud Chemistry Case (http://box.mmm.ucar.edu/individual/barth/TracerTransportDeepConvection.html). An intercomparison of these models will show how well-reputed models perform when simulating the same storm, giving a range of results that agree reasonably with observations.  The intercomparison case focused on the 10 July 1996 STERAO storm for which observations of carbon monoxide, ozone, and nitrogen oxides (NOx) are available.  Barth and Kim contributed results from the WRF-AqChem model. These results are being compared to those from Chien Wang (Massachusetts Institute of Technology), Jean-Pierre Pinty and Celine Mari (Laboratoire d'Aerologie, Toulouse, France), Ann Fridlind (NASA, Ames Research Center), Vlado Spiridonov (Hydrometeorological Institute, Skopje, Macedonia), Maud Leriche and Sylvie Cautenet (Laboratoire de Météorologie Physique, Clermont-Ferrand, France), and Ken Pickering, Lesley Ott (University of Maryland) and Georgiy Stenchikov (Rutgers University). Passive tracer transport show similar results among the models and agree fairly well with observations.  The intercomparison of NOx produced from lightning and of the soluble species, nitric acid, hydrogen peroxide and formaldehyde, is currently being pursued. 

 

Cloud Chemistry Process Studies - The Importance of the Cloud Drop Representation on Cloud Chemistry

Previous studies have shown that the representation of cloud drop microphysics affects the amount of sulfate produced by aqueous chemistry because aqueous sulfur chemistry depends on pH, and pH varies with drop size.  Because other aqueous chemical reactions (e.g., those involving hydroperoxy radical and formic acid) also depend on pH, Barth is using a cloud parcel model coupled with gas and aqueous chemistry to investigate the importance of the model's cloud drop representation on cloud photochemistry.  Barth's study focused on ozone, hydrogen peroxide, formaldehyde and formic acid under remote and moderately-polluted chemical and aerosol conditions.  Results of the study showed that formaldehyde and formic acid are sensitive to the cloud drop representation, while ozone and hydrogen peroxide are not.

 

Snow/Ice

Mid-latitude Snow Chemistry Experiment

The MSI Group (Eric Apel) was selected to receive funds from the NCAR Director’s Opportunity Fund for a project entitled: “Investigation of snow-mediated photochemical processes at mid-latitudes”. This is a two-year project that is being conducted at the CU Alpine Research station at Niwot Ridge.  Eric Apel, Elliot Atlas (now at University of Miami), Aaron Swanson, and Barry Lefer (now at University of Houston) are collaborating on this project with Russell Monson and Mark Williams (CU) and a number of colleagues from other universities.  Two students, from the Louis Pasteur Institute in France, played an active role, under the direction of Apel, in the set-up of the experiment last winter and the initial data analysis.

Objectives of the study included increasing our understanding of key aspects of photochemical processes in snow that may be occurring at mid-latitudes. The combination of biological and photochemical processes within a snow covered terrain could have significant impacts on the seasonal budgets of many trace gas species, along with important effects on the chemistry of the boundary layer atmosphere.  Figure 23 shows the students, Maxime Jaeger and Vincent Schell, participating in the hard work required to set up the experiment.  Figure 24 shows a view of the sampler that was constructed and placed in the snow. The sampler was designed to obtain depth profiles of targeted VOCs in the interstitial air throughout the snow pack and above the snow pack.  Figure 25 shows Swanson obtaining snow samples to be analyzed for physical and chemical makeup in a recently excavated snow pit.

 Figure 23: Students transporting equipment to the site.

Figure 24: Sampler constructed and placed at the site for sampling the interstitial air in the snow pack.

 

 

Figure 25: After digging a snowpit, Swanson takes snow samples.

 

A significant fraction of the trace-gas emissions are thought to be products of biomass growth in microbial and fungal communities brought on by thermal insulation of the soil by the snow (Swanson et al., 2004, and references therein). The MSI Group is investigating whether the emissions from wintertime activity are an important source of VOCs to the atmospheric background mixing ratios and on what scales, local or global. Figure 26 shows some results that were obtained during one of the experiments conducted in spring 2004.

Figure 26: Depth profiles of select VOC species during spring 2004 experiment.

 

The Group is continuing to work up the data collected throughout spring 2004, in anticipation of next year’s experiment. From Figure 26, it is clear that the terpenes show large concentration gradients and high relative concentrations near the soil surface. There are some clear differences in depth profile shapes for a number of species. With the data, species that increase significantly with depth and those which show losses to the soil surface can begin to be categorized to help us understand consumption and production processes for a variety of species.  This data will be compared to data previously collected at this site by Swanson and co-workers, as well as data collected at other sites.

 

Deployment of a Snow Pack UV Radiation Profiler to Summit, Greenland

Sunlit snow has been shown to be one of the most photochemically active, and strongly oxidizing, regions of the entire troposphere, rather than simply a passive sink for the products of tropospheric chemical processing.  Photolysis of nitrate initiates very active chemistry that leads to the release of a number of important trace gases.  Initial measurements suggest that just above sunlit snow the production of HOx from photolysis of HCHO, HOOH, CH3CHO and HONO are all significant, and collectively dominate over photolysis of O3.  The net result is a large enhancement of OH and HO2 in air just above the snow.  Oxidation by OH is the main sink for a number of gases important for climate change and stratospheric O3 depletion, so this enhancement may perturb chemistry in much of the free troposphere and also modify the chemical records of atmospheric composition ultimately preserved in glacial ice.  While recent work has shown that photochemical and physical processes in the snow pack can impact the chemistry and composition of both the atmosphere and snow pack, these processes are, in general, poorly understood.  This is especially true for the processes that produce and consume OH and HO2.

In an effort to better understand this photochemical environment, Barry Lefer and Rick Shetter of the ARIM Group deployed a custom-profiling spectroradiometer to determine the intensity of solar UV radiation at five different depths in the surface snow pack.  This instrument serially samples the radiation field from 290 to 560 nm from five different fiber optic cables inserted into the snow pack at different depths between 1 and 150 cm.  These snow pack profiles of solar irradiance were used to determine the attenuation rate of UV in the snow pack and how this varied with changes in environmental variables such as snow pack density, soot content, solar zenith angle (SZA) and overhead ozone column.  Given the isotropic nature of the radiation field in the snow pack, the measured irradiance spectra were converted to actinic flux spectra and the photolysis frequencies of several important snow pack photochemical reactions were calculated for the different sampling depths.  This data has helped determine that the photic zone (or photochemically active region) of the snow pack is only the top 15 cm of the Greenland snow pack.  This instrument was deployed for the months of March, April and May 2004 at the Greenland Summit Ice Camp (Figure 27) as part of the NSF-funded Collaborative Research Grant titled: “Impact of snow photochemistry on atmospheric radical concentrations at Summit, Greenland.”

 

Instrument Description

The NCAR Snow Profiling spectroradiometer (NSPS) instrument consists of a small cosine-corrected irradiance probe (Ocean Optics), 5m fiber-optic with high UV throughput (Ocean Optics), a precision computer controlled dovetail slide (Velmex), a double monochromator (CVI Digikrom CM 112), a photomultiplier tube with a bialkali photocathode (Electron Tubes, LTD), a custom four-stage current-to-voltage amplifier and a PC computer for fully automated data acquisition and system control.  Spectra from 280 to 560 nm are scanned every 30 seconds.  The spectral band pass full width at half maximum (FWHM) for this optical system is 1.0 nm.  Absolute spectral calibrations are performed with a National Institute of Standards and Technology (NIST) traceable 1000 Watt QTH irradiance standard in the NCAR laboratory before and after instrument field deployment.  Field calibrations are performed with 250 W secondary QTH lamps every four-to-five days to assess the relative stability of the instrument sensitivity.  Wavelength calibrations of the monochromator are performed in conjunction with each sensitivity calibration using the emission lines from a mercury lamp to track any drift in the monochromator wavelength assignment.

Figure 27: Summit, Greenland snow photochemistry camp.

 

A Scanning Actinic Flux Spectroradiometer was also deployed to Greenland to measure the UV radiation incident to the snow pack surface.  The quartz optical collector for this system was mounted on the roof of the mobile sampling laboratory and had a 30 cm artificial horizon to limit the field of view to 2pi steradians to minimize the influence of reflected light from the other sampling inlets.

It is quite difficult to measure snow pack radiation levels due to issues of self-shading by the optical sampling inlet.  To this end, the ARIM lab has selected miniaturized Teflon sampling inlets (approximately 1 cm in diameter and less than 2.5 cm long), which attach directly to the end of a fiber optic using an SMA connector. These miniature-sampling inlets were inserted into the snow pack at a location near the gas sampling activities at five different depths between the surface and one and a half meters.  Each sampling inlet was attached to a 5m fiber optic cable that was connected to the same spectroradiometer.  The snow spectroradiometer serially samples each of these five depths, thus collecting a complete snow profile every two and a half minutes. The above-snow spectroradiometer continuously measured the actinic flux reaching the snow surface, which can account for any changes in the light environment (e.g., due to clouds) while a specific snow profile is being collected.

Antarctic Polar Plateau

One of the more fascinating recent advances in atmospheric research has been the recognition of the central role of photochemical processing within the snow pack on the chemistry of polar plateau boundary layer air.  The most dramatic effects of the snow pack emissions appear to exist in Antarctica where, as part of the Antarctic Tropospheric Chemistry Investigation (ANTCI) field experiments, Fred Eisele, Lee Mauldin, Bruce Henry, and Edward Kosciuch (all members of the ACD Photochemical Oxidation and Products [POP] Group), in collaboration with colleagues from GIT and several other universities, have gained major new insights into the vertical and horizontal distribution of NO and NOy.  Very high levels of NO have been previously reported at the South Pole ground site with concentrations in the hundreds of pptv (parts per trillion by volume).  These concentrations were shown in recent Twin Otter flights to be maintained well beyond the near vicinity of the South Pole.  These high levels persisted in near surface air samples for ~ 300 km both upwind and downwind of the pole.  It now seems likely that somewhat similar levels will be found over much of the plateau region.  The influence of these snow surface emissions of NOx was also observed to extend into the free troposphere.  NO concentrations on the order of tens of pptv were still observed up to a half a km above the snow surface, suggesting that OH concentrations, and, hence, oxidation rates are very likely to be enhanced above those previously expected for this region.  This observation is quite significant because it now demonstrates that a much larger fraction of the troposphere has an enhanced oxidation capacity and it is through this region that sulfur and other reactive compounds must be transported in order to reach the Pole and other plateau locations.  Thus, reactive compounds such as DMS and SO2 can be oxidized during transport far more quickly than previously calculated in model simulations.  This decreased DMS lifetime is consistent with past and present observations showing very low concentrations of DMS, SO2, and gas phase H2SO4, and MSA at the South Pole.  Additional Twin Otter flights near the coast addressed another previous mystery: Why have past observations of NO concentrations at the coast been so much lower than those observed at the Pole?  Several flights along the Trans-Antarctic Mountains, particularly across the base of large glacial flows such as Byrd Glacier, at times revealed very high concentrations of NO and NOy  (hundreds of pptv).  These enhanced concentrations are presumably the result of NO-rich boundary layer air, which, due to the katabatic flow, is transported from the plateau down these glacial valleys resulting in the transport of this NOx enriched air to a few select outflow regions at the coast.  The potential importance of these results for understanding ice core MS/sulfate ratios is the suggestion that the ratios of these compounds deposited to the snow surface may well depend on the distance from the coastal source of sulfur and the proximity of glacial outflow relative to sulfur inflow.

Some preliminary results arising from the in situ ground-based South Pole measurements have also been obtained.  For example, PAN should have an atmospheric lifetime of months over Antarctica, and therefore could provide a mechanism for transporting reactive nitrogen from mid latitudes to the polar region.  The results of PAN measurements at the Atmospheric Research Observatory (ARO) building at the South Pole, however, suggest that there are insufficient PAN concentrations to significantly affect the nitrogen chemistry over the plateau.

Early in the study, several instruments were operated during a nearly complete solar (~85% occlusion) eclipse.  Since the sun height normally changes little during our study period, this eclipse was a rather unique opportunity to observe changes in photochemically-generated compounds with nearly an order of magnitude change in UV light as shown in Figure 28.  Several interesting relations are demonstrated by this figure.

Figure 28:  Some interesting South Pole boundary layer photochemistry observed during the near total solar eclipse that occurred on November 23, 2003. Since the sun only sets and rises once a year at the South Pole, this unique and rapid photochemical transient will be the basis for a modeling case study. 

 

Prior to the eclipse, the anti-correlation between NO and OH can be seen.

·        Above ~175 pptv of NO, NOx levels are large enough that the reaction of OH with NO2 becomes a significant sink for OH, thus a decrease in NO (and hence NOx), causes an increase in OH.

During the eclipse, the percentage change in OH is larger than the percentage change in UV radiation (J(O1D)).

·        This observation reflects the fact that primary production of OH, via O(1D) production, has been decreased, while at the same time the steady state partitioning between NO and NO2 is shifted to primarily NO2, an OH sink. Thus during the eclipse, the production of OH is decreased while the sinks for OH are increased, causing the larger observed percentage change.

There is a time delay between UV and the response of NO.

·        The time delay in the response of NO to the decrease in UV reflects the lifetime of NO in the atmosphere. The delay in response to the increase in UV reflects the photolysis lifetime of ambient NO2 and nitrate in the snow pack (the source of much of the NOx in the South Pole boundary layer).

Also note the small OH concentrations (~4x104 molecule cm-3, or ~2 parts per quadrillion by volume) that the instrument is capable of measuring.

A new, compact mass spectrometer instrument has been designed and built this past year in order to allow OH to be measured on a Twin Otter aircraft during the upcoming ANTCI 2005 study.  This instrument, when complete, should be four to five times smaller and lighter than the existing four channel system but still provide similar sensitivity for measuring OH, H2SO4 and MSA.  The new system makes use of advances in mass spectrometer and octopole lens design and will serve as a prototype for a future HIAPER OH instrument.

 

Research Groups

Atmospheric Radiation Investigation and Measurement (ARIM)

Laboratory Kinetics Group (LK)

Measurement, Standards, and Intercomparisons (MSI)

Photochemical Oxidation and Products (POP)

Regional and Process Studies (RPS)

 

Chemistry in the Climate System

The global climate system is a composite of local, regional, hemispheric, and interhemispheric processes that occur from the surface to the upper atmosphere on time scales of minutes to decades.  The role of chemistry in this complex system involves multiple interconnected components with a range of temporal and spatial scales.

A primary focus of the chemistry-climate modeling studies in ACD is to evaluate direct anthropogenic and biogenic emissions both spatially and temporally, to determine the influence of  transport processes on the distribution of those emissions, and to examine the impacts of the emissions on atmospheric chemistry.  In addition, the modeling studies also examine aerosol distributions, formation processes, influence on chemical species, and radiative properties and impacts including indirect aerosol and cloud effects.  These studies, based on the current climate system, additionally provide a foundation for model simulations designed to study the influence and feedbacks of climate and global change on chemistry of past and, most importantly, future climate regimes.

Focused studies of biogenic emissions are a key aspect of ACD research on biogeochemical cycles.  These studies include measurements of emissions and vertical flux of many species, including VOCs, NOy, O3, and CO.  These measurements have been collected on a broad range of spatial scales from leaf, plant, and canopy scales, through to regional scales.  The implications of these flux determinations on the local, regional, and global atmosphere are evaluated through the incorporation of empirically-based flux parameterizations in numerical model simulations.

The upper troposphere/lower stratosphere region of the atmosphere plays a crucial role in the climate system because of the radiative impacts of water vapor, ozone, and aerosols in that region.  ACD research in the UTLS region is focused on understanding the distributions of ozone and water vapor and how photochemistry, multiphase chemistry, convection, and stratosphere-troposphere exchange influence those distributions.

The role of the middle atmosphere (the region between the lower stratosphere and the lower thermosphere) in the climate system is not well characterized.  ACD research in this area is focused on understanding the broad interactions between chemistry, radiation, and transport using a combination of models and measurements/calculations of chemical constituents and energy budgets.

 

Climate Simulations

The distribution and abundance of radiatively active gases and aerosols are important determinants in the Earth's radiation budget and the state of the climate system.  Atmospheric chemistry and transport are key factors in determining the abundance and distribution of these trace gases and aerosols.  Changes in the chemistry-climate-biogeochemistry system are expected to be strongly coupled with important, but as yet not well quantified, feedbacks.  ACD scientists are evaluating this system through model development and simulations of various climate states.

 

Present-Day Climate

Tropospheric Ozone Interannual Variability

Using the available ozonesondes data, Lamarque has studied the interannual variability of tropospheric ozone focusing on the Northern Hemisphere poleward of 40°N. This analysis shows that the spring ozone interannual variability is strongly related to the phase of the NAO (Lamarque et al., 2004).  Lamarque, Hess, and Mahowald are in the process of extending this analysis for a further understanding of the ozone budget in the troposphere. 

 

Studies of the Arctic Oscillation

The study of the Arctic oscillation in tropospheric ozone by Hess and Lamarque was one of the first to show the influence of the Arctic oscillation on tropospheric ozone. It is shown in both a data analysis of ozonesondes and in model simulations. The NAO explains a significant amount of the interannual variability of springtime ozone over North America (Lamarque and Hess, 2004).

 

Role of Convective Versus Synoptic Transport

Hess examined the relative importance of convective versus synoptic transport and the seasonal variation and the atmospheric regions affected by these modes of transport. This study is important for understanding the different processes which influence the UTLS (and was summarized during the UTLS workshop). These modes of transport affect the chemistry in different ways (Hess, submitted).

 

Santa Fe Project

As an outcome of the Chemistry-Climate Interactions workshop organized by Lamarque and Jeffrey Kiehl (CGD), a project for the study of nitrogen deposition on the biosphere and its impact on the carbon cycle was designed. Lamarque, in collaboration with various groups (GISS, UKMO, Lawrence Livermore, UCI, Max-Planck Mainz, Max-Planck Hamburg, IPSL Paris) has combined and analyzed the results of nitrogen deposition. These results have been presented as a poster at the International Global Atmospheric Chemistry (IGAC) meeting. In addition, this model intercomparison will also be used for a paper on the ozone radiative forcing in the 21st century.

 

Past and Future Climates

Intergovernmental Panel on Climate Change (IPCC) Simulations

Lamarque, in collaboration with Hess, Emmons, Lawrence Buja (CGD), Warren Washington (CGD), and Claire Granier (NOAA/IPSL), has performed MOZART simulations from 1890 to 1990 in 20-year increments.  The simulated ozone field has been used by the CCSM group in their simulations of the 20th century climate for the next IPCC Assessment.

 

Model Development

Off-line Community Atmosphere Model (CAM)

Phil Rasch (CGD), Hess, Stacy Walters, and Francis Vitt have successfully created an off-line-transport version of CAM, the transport model embedded within the CCSM framework. This model imports meteorological fields from other sources (e.g., NCEP, ECMWF) into the CAM model instead of using internally generated fields. This provides the opportunity to simulate the transport and chemistry of trace constituents (reactive and passive species and aerosols) using meteorological analysis. These distributions can then be compared with measurements on an episodic basis and used in process studies. This model introduces a new capability into the CCSM framework and reduces the software engineering effort required for maintaining multiple chemical transport models within the same institution. It also allows improvements to the consistency of representations of physical processes within the model and allows all components of the climate system to influence the chemical simulations. We anticipate that this model will replace the MATCH and MOZART CTMs.  

Simple trace constituents have been successfully simulated in the off-line model using meteorological fields from NCEP, ECMWF and CAM. These tracers include an ozone-like tracer and other diagnostic species. The trace constituent distributions have been compared against those produced in MOZART, online CAM and MATCH with good results. This model is now coded to the computational standards of the CCSM. Chemistry is currently being implemented into the off-line-CAM model.

 

Interactive Community Atmosphere Model (CAM3)

Lamarque has completed the implementation of interactive chemistry (including aerosols) from the MOZART model into CAM3, using the WACCM (Whole Atmosphere Community Climate Model) framework.  The radiative coupling is done through the ozone distribution and the aerosol distributions.  This work has been presented at the CCSM workshop in July and will be the basis for the released version of CAM3 with interactive chemistry. This work is in collaboration with CGD (Rasch and Mahowald) and Walters (WACCM).

Lamarque has expanded the aerosols package developed by Tie to have a better representation of the formation of ammonium nitrate.  This package is now running in the newest version of MOZART and in CAM3.  In addition, several modifications were made to the modeling of dry deposition in MOZART in order to accommodate aerosols.  Finally, interactive biogenic emissions of isoprene and soil NOx emissions are now part of MOZART.

 

Model for Ozone and Related Chemical Tracers (MOZART)-4

MOZART-4 is an update to the MOZART model published by Horowitz et al. in 2003. This update has been necessary to transform MOZART into a state-of-the-art chemical transport model and to make it available to the community at large. The updates to MOZART will be included in the online and off-line CAM with chemistry. Numerous updates have been implemented by Lamarque, Emmons, John Orlando, Geoff Tyndall, Tie, Walters, and Hess.  The improved chemical mechanism now considers three classes of large anthropogenic hydrocarbons: a large alkane (butanes and larger), a large alkene (butenes and larger) and an aromatic species (toluene). Reaction rates have been updated. Updated emissions have been constructed consistent with the new chemical mechanism. The ability to input multi-year emission datasets has been added. Lower boundary conditions can now be fixed for long-lived species (e.g., H2 and CH4). Interactive emissions are implemented, e.g., for isoprene and soil NOx, as these depend respectively on the model temperature and photosynethic radiation and on the calculated soil wetness.  The aerosol parameterizations have been updated.  Photolysis frequencies are calculated with the fast TUV code, allowing online calculations consistent with model clouds and aerosols. Dry deposition is interactive for all species and with an additional parameterization of the effect of microbes on the dry deposition of CO and H2. The lightning parameterization has been updated.  New output fields have been enabled. A synthetic ozone field can be used in the stratosphere so as to constrain the stratospheric-tropospheric flux of ozone to reasonable values when running MOZART with analyzed wind fields.  Interactive water fields, instead of diagnosed water, have been implemented.  Finally, a new website documenting the model, related publications, and ongoing research in global tropospheric modeling has been developed which allows downloading of the source code.

 

Tracer Version of MOZART-4

A tracer version of MOZART-4 has been developed by Hess, Vitt, and Gabrielle Pfister.  This tracer version allows reading a number of chemical species into the model and specifying their chemical sources. For example, it allows the input of an OH field and the source of CO from the oxidation of hydrocarbons. The tracer version of MOZART-4 will be used for inverse modeling studies at considerably less expense than running the full version.

 

Adjoint Version of MOZART

Hess, Gabrielle Petron, and Baker developed most of the components for an adjoint version of the MOZART code during this year. The basic framework for the MOZART adjoint (i.e., running the model backwards) and the appropriate check pointing has been implemented. An adjoint of the diffusion code and convective code has been developed. In addition, an optimization code to solve for emissions has been developed.

 

Research Group

Global Modeling

 

Biogeochemical Cycles

The mission of the Biosphere-Atmosphere Interactions (BAI) Group is to advance understanding of the role of biosphere-atmosphere interactions in the Earth system and predict its response to human perturbations. This is being accomplished through multidisciplinary field, laboratory and modeling studies of the processes controlling these interactions on various scales (e.g., leaf to canopy to regional/global).  BAI members during FY04 included Alex Guenther, Jim Greenberg, Peter Harley, Thomas Karl, Ryan Schnell, Andrew Turnipseed, and Christine Wiedinmyer. 

 

Laboratory Studies

BAI scientists (Guenther, Greenberg, Harley, and Karl) are using laboratory facilities to characterize the processes that control biomass burning and biogenic emissions. Biomass burning studies were conducted in the ACD laboratory roasting/burning chamber facility in collaboration with Hans Friedli (ASP) and in the United States Department of Agriculture Missoula fire laboratory burn facility in collaboration with Robert Yokelson and Theodore Christian (both of University of Montana). Biogenic emission studies were conducted in the ACD phytotron and growth chamber facilities in collaboration with Emiliano Pegoraro (Edinburgh University, U.K.), Allison Steiner (University of California, Berkeley) and Teresa Nunes (University of Aviero, Portugal).

The laboratory biomass burning studies demonstrated that oxygenated volatile organic compounds (VOCs) and nitrogen compound emissions from fires are higher than most previous estimates and likely have an important role in fire dynamics (i.e., fuel ignitability) and regional air quality. This research also suggests that emissions of some compounds from smoldering fires (including charcoal production and post flaming phase pyrolysis) are underestimated in existing fire emission inventories.   Three manuscripts (Karl et al., Greenberg et al., Christian et al.) describing these results are in preparation for submission to peer-reviewed journals.

The laboratory biogenic emission studies have shown that isoprene emission is more resistant and recovers more quickly from drought than does photosynthesis and stomatal conductance. Isoprene emission rates show a strong correlation with leaf water potential, providing a useful parameterization for including the effects of drought stress in isoprene emission models. Other experiments have demonstrated that sesquiterpene emission rates from some important tree species are comparable to monoterpene emission rates and exhibit similar temperature dependence. Biogenic methanol emission rates were observed to vary across and within plant species by at least an order of magnitude. Leaf age was identified as the major source of within species variation in methanol emission.  Observed light dependent monoterpene emissions varied as a function of growth temperature and certain monoterpenes (e.g., ocimene) were released at elevated levels in response to temperature stress.  This work is described by Pegoraro et al., Harley et al., and Nunes et al., which are in preparation for submission to peer-reviewed journals in late 2004.

 

U.S. Field Studies

BAI scientists investigated biosphere-atmosphere interactions with six U.S. field studies during FY04 and analyzed data from an additional three U.S. field studies. The six FY04 field studies supported the research of investigators from five universities. A study of the contribution of biogenic isoprene emission to regional aerosol and oxidants was conducted at a poplar plantation in northern Oregon and was conducted in collaboration with Brian Lamb, Halvor Westberg and Adam Hill (Washington State University).  The potential allelopathic role of biogenic VOC emissions from invasive Artemesia shrubs in New York was conducted in collaboration with Jed Sparks and Jacob Barney (Cornell University). An aircraft investigation of cicada outbreaks in Indiana was conducted in collaboration with Paul Shepson (Purdue University) and showed that the emissions from decaying cicadas did not have a significant impact on atmospheric chemical composition. Trace gas fluxes over a Colorado grassland were measured in collaboration with Matt Dunn (ASP/CU) and James Smith (ACD).  The observations show that the grassland was a significant source of methanol and a sink for acetic acid and methyl acetate. Ozone deposition was measured at the Niwot Ridge, Colorado AMERIFLUX site in collaboration with Russell Monson (CU).  The negative impact of high O3 events on the subalpine forests downwind of Denver, Colorado are minimized by their occurrence during late afternoon-early evening periods when plant activity is low due to both water stress and low light levels. Studies of ammonia fluxes from soybean fields in North Carolina were conducted in collaboration with John Walker (North Carolina State University and United States Environmental Protection Agency [USEPA]). Significant fluxes were observed and the results demonstrated the utility of the ammonia CIMS system designed and built by ACD.

FY04 efforts also included a workshop, database development, data analysis and manuscript preparation associated with the Chemical Emissions, Losses, Transformations and Interactions with Canopies (CELTIC) study in Duke Forest, North Carolina led by BAI in collaboration with Chris Geron, Bob Arnts (USEPA) , Walker, Jose Jimenez, Darin Toohey, Alice Delia (CU), Sparks (Cornell), Mark Potosnak (Desert Research Institute), Greg Huey, David Tanner, Darlene Slusher and Robert Stickel (GIT), Kolby Jardine and Bradly Baker (South Dakota Institute of Mining and Technology), Jose Fuentes (University of Virginia) Will Vizuete (University of Texas), Fred Mowry and Jeff Herrick (Duke University), Francesca Rapparini (Istituto di Biometeorologia, Italy), Rei Rasmussen (Oregon Graduate Institute).  The CELTIC results indicate that isoprene emission increases with elevated ozone and, on a canopy scale, with elevated CO2.

Future changes in ozone and CO2 could thus change regional isoprene emission rates leading to feedbacks. The pine plantation forest floor (soil and leaf litter) was a significant sink of methanol, acetone, acetaldehyde and isoprene. This is not well represented in existing models and could lead to overestimated ambient concentrations. Substantial sesquiterpene emissions observed from pine trees could be the dominant source of biogenic secondary organic aerosol mass under certain environmental conditions. PAN (and PAN-like compounds) were deposited at a much faster rate than is predicted by current models by a factor of 3-5.  This has significant implications for the lifetime of PAN in the atmosphere and its role as a transporter of reactive nitrogen in the atmosphere. Simultaneous observations of biogenic VOC and total organic aerosol during CELTIC allowed new constraints on aerosol yields and OH formation due to ozonolysis. The average aerosol yield for alpha-pinene, beta-pinene and d-carene are higher than calculated, supporting recent laboratory studies showing that polymerization reactions could enhance aerosol partitioning (Figure 29). Based on observed isoprene decay within the canopy, the upper limit of nighttime OH mixing ratios is less than reported measurements for other forests.  Estimates of biogenic contributions to secondary organic aerosol mass at Duke Forest suggest that biogenic sources dominate which is somewhat surprising for this moderately polluted site.

Figure 29: Comparison of SOA growth between different modeling approaches compared to measured gradients (red circles).

 

Analysis and publication of two other previous U.S. studies were completed in FY04.  A tower flux study of isoprene and oxygenated VOC emissions from a northern Michigan deciduous forest was conducted in collaboration with Raymond Fall (CU) and Armin Hansel (University Innsbruck, Austria). The differences can be explained by the different physiological and phenological processes controlling these emissions. The multiscale (enclosures, tower, tethered balloon, aircraft) Ozarks Isoprene Experiment (OZIE) study was conducted in collaboration with Brian Lamb and Halvor Westberg (Washington State University), Jay Turner (Washington University), Paul Palmer (Harvard University), Geron and Thomas Pierce (USEPA) and demonstrated that central U.S. oak forests and woodlands have very high isoprene emission rates resulting in elevated regional formaldehyde concentrations.  This formaldehyde is often transported northward and eastward towards urban centers such as St. Louis and Chicago, and participates in the production of ozone (Figure 30). Current photochemical models underpredict the magnitude of formaldehyde produced by isoprene oxidation which leads to incorrect chemistry simulations within the urban centers.

Figure 30: Hourly-averaged formaldehyde concentrations for 06:00 CDT on July 21, 1998, as modeled by CAMx. Winds on this day were predominantly from the south-southwest. A plume of elevated formaldehyde can be seen being transported from the forests of the Ozarks towards the northeast and into the Chicago urban area. The majority of this formaldehyde has been formed from the photooxidation of isoprene emitted from the Oak forests of the Ozarks on the July 20.

 

International Field Studies

BAI scientists participated in international investigations of biosphere-atmosphere interactions in Brazil, Ireland, and Japan during FY04 and analyzed results from previous studies in China, Costa Rica, Brazil, and Finland.  The FY04 Chemistry And Production Of Smoke (CAPOS) study in the Brazilian Amazon used airborne and ground measurements to characterize the primary emission composition of VOCs and other gases from tropical fires and within aging plumes in collaboration with Robert Yokelson and Theodore Christian (University of Montana), Don Blake (University of California, Irvine), Paulo Artaxo (University Sao Paulo, Brazil), and Joao Caravalho (Center for Weather Forecasts and Climate Studies [CPTEC] of the National Institute for Space Research [INPE], Brazil). Additional background measurements were made at a primary tropical forest flux tower near Manaus, Brazil in collaboration with Potosnak, Artaxo, Julio Tota and Antonio Manzi (Brazilian National Institute of Amazon Research [INPA], Brazil).  Significant flux of monoterpenes was estimated from the vertical profile shown in Figure 31. The aircraft observations generally confirmed the emission profiles measured in the laboratory studies described above (Figure 32). The contribution of semi-volatile organic gases to secondary organic aerosol mass was studied in Japan in collaboration with Yoshizumi Kajii (Tokyo Metropolitan University).

Figure 31: Altitude profile of monoterpenes above the Z34 tower close to Manaus.

 

 

Figure 32: Comparison of emission profiles of identified compounds obtained by the PTRMS instrument between laboratory experiments (average of 30 experiments) conducted at the USFS fire lab in October 2003 and airborne measurements (35 samples from 10 fires) in 2004. All data are normalized to the biomass burning marker acetonitrile.

The results indicate that humidity plays a significant role in determining the uptake of some semi-volatile compounds. BAI scientists participating in the BIOFLUX field study on the Irish coast investigated biogenic fluxes of organic iodide compounds in collaboration with Colin O’Dowd (National University of Ireland), Liisa Pirjola (University of Helsinki, Finland) and Thorsten Hoffman (Institute of Spectrochemistry and Applied Spectroscopy [ISAS], Dortmund, Germany).  A tethered balloon system was used to characterize vertical gradients of several alkyl halides including di-iodomethane, ethyl bromide and ethyl iodide. Concentrations decreased with height indicating a surface source of these compounds which are believed to be involved in new particle formation.

Two manuscripts were published in FY04 (Spirig et al., and Boy et al.) describing BAI results from the Origins of Secondary Organic Aerosol (OSOA) study that was conducted at a boreal forest site in Finland in collaboration with Christoph Spirig (Swiss Federal Institute of Technology [ETH] Zurich, Switzerland), Michael Boy and Markku Kulmala (University Helsinki, Finland). Total monoterpene oxidation rates during the OSOA study were not correlated with particle production events, but there was a strong correlation with ozone indicating that more ozone reactive biogenic compounds, such as sesquiterpenes, may make an important contribution. Vertical gradients of particles above the forest suggest that particle growth occurs throughout the boundary layer.

Tropical forest biogenic emissions were studied in the eastern Amazon (Brazil) in collaboration with Luciana Vanni Gatti and Carla Trostdorf (Energy and Nuclear Research Institute [IPEN], Brazil) and in Costa Rica in collaboration with Deborah Clark (University of Missouri), Sparks, and Potosnak. Seasonal isoprene variations in the Amazon were much higher than expected (more than a factor of 3 higher in the dry season).  Tropical forest ecosystems in both Brazil and Costa Rica were both a significant source (daytime) and sink (nighttime) of methanol, acetone, and acetaldehyde.  Dry deposition velocities of these and other (e.g., methyl vinyl ketone, methacrolein, and acetonitrile) compounds were a factor of 10-20 higher than estimated from existing deposition models which has important implications for regional and global chemistry and transport models. This work is described in Greenberg et al., 2004; Harley et al., 2004, Trostdorf et al., 2004, and Karl et al., 2004.

Baker et al., 2004, and two manuscripts in preparation describe studies of the impact of land cover change on biogenic emissions from Chinese landscapes that were conducted in collaboration with Baker, Rassmussen, Bai Jianhui (Institute of Atmospheric Physics [IAP] Chinese Academy of Sciences), Susan Owen (Lancaster University), and Geron. Chinese rubber tree and oil palm plantations have much higher terpenoid emissions than native tropical forests. This suggests that there has been and continues to be significant increases in biogenic VOC emissions in some tropical regions of China.  Severe drought results in a dramatic reduction in these emissions demonstrating the equally important role of climate change.

 

Regional Modeling Studies: U.S.

Wiedinmyer and Guenther investigated biosphere-atmosphere interactions in the U.S. using regional chemistry and transport models. FY04 studies included an investigation of the impact of future climate and land cover on regional air quality in the Pacific Northwest and north central U.S. in collaboration with Brian Lamb (Washington State University), Cliff Mass (University of Washington) and Susan Fergusen (U.S. Forest Service) and a study of the contribution of sesquiterpenes and other biogenic VOC emissions to secondary organic aerosols in the eastern U.S. in collaboration with Jana Milford (CU). Both of these projects were initiated in FY04, and efforts were directed at setting up the regional air quality modeling system and developing the emission scenarios.

 

Regional Modeling Studies: International

Wiedinmyer, Sreela Nandi (ASP/ACD Postdoctoral Fellow), and Guenther investigated biosphere-atmosphere interactions in China, Brazil, and Mexico using regional chemistry and transport models in FY04.  The contribution of biogenic VOC emissions to oxidant and particle production in China was studied in collaboration with Xiaoping Wang and Denise Mauzerall (Princeton University). The results indicate that future growth in China’s fossil fuel emissions will lead to costly decreases in public health and crop productivity. Much of this region is VOC-limited so changes in biogenic VOC emissions will have important consequences for air quality.  The BAI Group, along with Hsiao-ming Hsu (MMM and NCAR’s Research Applications Program [RAP]), investigated the influence of biomass burning on regional air quality in the Brazilian Amazon along with a detailed sensitivity study of emission inputs which demonstrated that there are large difference in the fire emissions predicted using different methods recommended in the literature. The BAI Group also supported regional simulations of air quality in Mexico in preparation for the ACD Megacity Impacts on Regional and Global Environments [MIRAGE] study (Xuexie Tie, ACD).

 

Global Modeling Studies

Wiedinmyer and Guenther investigated global scale biosphere-atmosphere interactions in FY04 using global chemistry and transport models. The contribution of biogenic VOC emissions to global organic aerosol was examined in collaboration with Joyce Penner (University of Michigan). The study showed that uncertainties in biogenic VOC emissions are a significant contributor to the total uncertainty associated with estimates of global radiative forcing of aerosols. A biogenic VOC model was integrated into the NCAR Community Climate System Model [CCSM] Land Surface Model [LSM] and used to investigate the sensitivity of emissions to climate and land cover in collaboration with Sam Levis and Gordon Bonan (CGD). Biogenic VOC emissions were sensitive to climate, and the estimated interannual variability exceeded 10% of the estimated annual anthropogenic emission estimates used for the IPCC emission scenarios. Finally, a study examining interactions among global change (climate and land cover), biogenic isoprene emissions, and the chemical composition of the atmosphere was completed in collaboration with Tie, Ronald Neilson (U.S. Forest Service), and Claire Granier (CNRS).  Climate and land cover-driven changes in biogenic VOC emissions impacted simulated regional surface ozone concentrations by as much as -30% to 50% under certain emission and climate scenarios. The ozone production chemistry was shown to change under different emission scenarios (i.e., NOx versus VOC) and has implications for unhealthy ozone concentrations and future ozone abatement strategies (see Figure 33).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 33: Change in LN/Q for the month of July for [(FUTVEG-CURCLIM) – (CURVEG-CURCLIM)] (top) and [(FUTVEG-FUTCLIM) – (CURVEG-CURCLIM)] (bottom).

Model and Database Development

Guenther and Wiedinmyer also developed biogenic and fire emission models and databases for the scientific and air quality regulatory communities. FY04 accomplishments include the initial release (user’s guide and files are available on the NCAR community data portal, https://cdp.ucar.edu/) of the Model of Emissions of Gases and Aerosols from Nature (MEGAN) which predicts biogenic emissions on a global scale at 1 km resolution (Figure 34). MEGAN was also integrated with the NCAR global models, MOZART and the Community Land Model (CLM), and an effort was initiated to integrate MEGAN with regional air quality models. In addition, a modeling framework was developed to predict daily emissions from fires for all of North America at a 1 km resolution for easy use in regional air quality model simulations. Fire emission inventories developed by this model will allow air quality modelers to include fire emissions with their model simulations and determine if fire emissions have a large impact on their air quality (Figure 35).

Figure 34: Global annual isoprene emission distribution for the year 2000 estimated by the MEGAN model.

Figure 35: Estimates of fire emissions of PM 2.5 (particulate matter less than 2.5 mm) for Louisiana.

 

Instrument Development

Turnipseed, Guenther, Greenberg, and Karl developed instruments for investigating biosphere-atmosphere exchange in FY04. This included a Disjunct Eddy Accumulation (DEA) system that captures and stores air based on the vertical wind direction and speed.  The concentrations in these stored samples (along with wind statistics) can then be used to determine fluxes of chemical trace species which are difficult to determine by other flux techniques which often need fast (< 1 s) measurement times.  This project was in collaboration with Lamb and Mount, Shepson, and Steve Shertz (ATD).  Two separate systems developed and evaluated in FY04 allow for DEA flux measurements of volatile organic compounds (VOCs) from both a tower and an aircraft platform. 

 

Research Group

Biosphere-Atmosphere Interactions

 

Integrated Study of Dynamics, Chemistry, Clouds, and Radiation of the Upper Troposphere and Lower Stratosphere (UTLS)

The UTLS region is of critical importance for understanding long term global or climate change.  The UTLS is a region where ozone is an effective greenhouse gas, and where water vapor, cirrus clouds, and aerosols each make a significant contribution to the radiation budget.  The UTLS is also a region where transport processes that couple the stratosphere and troposphere occur on a multitude of scales, which when combined with the strong vertical gradients in many chemical constituents, present a challenge to observational techniques and numerical models.  Chemically, the UTLS region represents a transition in the nature of the mechanisms of ozone production and loss.  ACD scientists are involved in studying various aspects of transport and chemistry in the UTLS as well as developing models and instruments to support these studies.

 

Satellite Data Analysis

The Satellite Data Analysis (SDA) Group (William Randel, Laura Pan, Bruce Henry, Steven Massie, and Fei Wu) focuses on studies of global scale chemical behavior using satellite measurements, meteorological data sets, and model simulations. Recent work has focused on chemical and dynamical behavior of the tropopause region, both in the tropics and extratropics, aiming to understand and quantify the processes which contribute to coupling in the UTLS.

The tropical tropopause layer (TTL, ~12-17 km) behaves as a transition between the convectively controlled troposphere and radiatively balanced stratosphere. Because air enters the stratosphere primarily in the tropics, the TTL serves as a boundary condition for the global stratosphere. Key science issues include understanding mechanisms of dehydration and cirrus cloud formation, and fast transport into and through the TTL (with relevance to short-lived chemical species).  Many features of the TTL are poorly observed by conventional data sets, and there are important uncertainties in the relationships between temperatures, winds, clouds and water vapor on large and small scales.  Current work in this Group is aimed at improved understanding of the TTL using new satellite observations, plus global model simulations.

William Randel has used high vertical resolution temperature profiles derived from Global Positioning System (GPS) radio occultation measurements to study temperature variability within the TTL, and links to large-scale tropical convection. Much of the TTL temperature variability is observed to occur in the form of eastward-propagating, planetary-scale Kelvin waves.  These waves have typical vertical wavelengths of ~4-8 km, which are well-resolved by the GPS measurements (but not by other satellite measurements).  The GPS results demonstrate that the global-scale Kelvin waves are directly forced by transient deep convection over Indonesia.  Furthermore, the Kelvin waves show strong coupling to the background winds, in particular, showing enhanced amplitudes coincident with the descending westerly shear phase of the quasi-biennial oscillation (QBO). 

Randel also leads a World Climate Research Program (WCRP) Stratospheric Processes and their Role in Climate (SPARC) initiative on detection, attribution and prediction of stratospheric changes.  This is an international effort aimed at quantifying past changes in stratospheric climate, understanding the responsible processes through model studies, and predicting stratospheric changes in the future.  As part of this work, Randel co-organized a SPARC workshop on Stratospheric Temperature Trends in Silver Springs, MD, in November 2003.  Randel and Andrew Gettelman were co-authors on a joint SPARC-IGAC white paper describing Chemistry Climate Interactions, which will form the basis for joint scientific activities during the next decade.  Randel is also involved as a lead author of an ongoing IPCC Report on Safeguarding the Ozone Layer and the Global Climate System, to be completed in 2005.

Gettelman and Randel are using tropical temperature and water vapor measurements from the AIRS instrument on the NASA Aqua satellite to characterize large- and small-scale variability.  This work is in collaboration with William Irion and Annmarie Eldering (NASA Jet Propulsion Laboratory [JPL]).  Gettelman has made detailed comparisons between AIRS data and aircraft measurements during pre-AVE (Atmospheric Variability Experiment), demonstrating high quality for the AIRS data.  Ongoing work includes quantifying the relationships between temperatures, water vapor and clouds, and understanding the effects of large-scale (satellite) vs. small-scale (aircraft) sampling.

The extratropical UTLS is a dynamically active region characterized by large variability, strong constituent gradients, and significant mass fluxes between the troposphere and stratosphere.  Pan has led several studies aimed at understanding constituent structure and variability in this region, using aircraft and satellite measurements together with model simulations. One project focuses on using tracer correlations to quantify the mixing of stratosphere and troposphere air near the subtropical jet.  Figure 36 shows an example of a stratospheric intrusion event observed during SONEX. The relationships between chemical tracers identifying stratospheric and tropospheric air (O3 and CO, respectively) are used to understand mixing and exchange and to compare to model calculations.

Figure 36: Color image shows the NASA Langley LIDAR (LIght Detecting And Ranging) measurements of ozone onboard NASA DC-8 research aircraft, October 29, 1997, during the SONEX campaign. The black dots are the thermal tropopause as measured by the Microwave Temperature Profiler. The ozone measurements show an intrusion of stratospheric air into the troposphere near the right edge of the image. The inset shows a scatter plot of CO-O3 measurements near the intrusion, provided along the aircraft flight track. The letters A, B, C, and D indicate the measurement locations for the “mixing line.”

 

Massie has focused on using satellite measurements to quantify tropospheric aerosols and pollution and their variability over time.  An analysis of Total Ozone Mapping Spectrometer (TOMS) satellite data shows a significant increase in tropospheric aerosols over China and India during 1980-2000 (Figure 37).  These increases are expected, due to large increases in population and SO2 emissions (converted to sulfate aerosols) in China and India, but this is the first study to quantify the changes based on satellite observations.  This analysis was in collaboration with Omar Torres (Joint Center for Earth Systems Technology, University of Maryland Baltimore County and the NASA Goddard Space Flight Center) and Steven Smith (Pacific Northwest National Laboratory, Joint Global Change Research Institute).

 

Figure 37: Winter averages of TOMS total aerosol optical depths, averaged for consecutive months from November through February for the China coastal plain and the Gobi desert. Aerosols over the Gobi desert are mainly due to desert dust, while aerosols over the coastal plain have a large contribution from sulfate.  Linear fits and decadal trends are indicated.

Mijeong Park (Seoul National University) is working with Randel and Rolando Garcia to study the structure and variability of the South Asian monsoon in the UTLS region, and its effect on trace constituent transport.  She is using satellite measurements of UTLS ozone and water vapor from AIRS, along with output from the Whole Atmosphere Community Climate Model, second version (WACCM2), to understand stratosphere-troposphere coupling associated with the monsoon circulations.  Results from WACCM2 and AIRS reveal consistent patterns of relatively high water vapor and low ozone within the monsoon anti-cyclone during summer. Variations in monsoon convective activity with 10-20 day periods are associated with fluctuations in anti-cyclone intensity and structure, and tracer variability. Analyses of observations and model results will be aimed at quantification of monsoon effects on stratosphere-troposphere exchange.

Additional UTLS related research is described in the Middle Atmosphere Studies section under WACCM results.

 

Model Development

Gettelman is leading a collaborative effort with Chris Webster (JPL), David Noone (CU), Andrew Dessler, Sun Wong (University of Maryland), and Natalie Mahowald (CGD), modeling isotopes of water in the atmosphere. Stable isotopes of water provide information about transport and budgets within the atmospheric hydrologic cycle. Heavier isotopes preferentially partition into condensed phases of water, and so the level of isotopes relative to a standard provides an integrated history of condensation. Thus heavy isotopes of water (chiefly HDO and H2-18O) can be used to understand the different pathways of transport in the upper troposphere. Specifically, air which contains significant quantities of evaporated ice will have a different set of isotopic ratios than air from which all the condensed phase has been removed.

Gettelman used an idealized model of the TTL to simulate the distribution of water isotopes, and compared against observations from in situ aircraft measurements. The model is able to reproduce the range of isotopic depletions observed in the data, and also reproduce individual episodes that mirror or depart from Rayleigh fractionation processes. The observations and the model simulation of HDO for a field campaign in the tropical upper troposphere are indicated in Figure 38, which also contains a theoretical curve of the isotopic ratio of a parcel lifted from the surface with all the condensate removed (a “Rayleigh distillation” curve).

Figure 38: The observations and the model simulation of HDO for a field campaign in the tropical upper troposphere are indicated in Figure 38, which also contains a theoretical curve of the isotopic ratio of a parcel lifted from the surface with all the condensate removed (a “Rayleigh distillation” curve).

The observations clearly indicate that water substance in the upper troposphere does not follow a Rayleigh distillation model. The fact that this simple model reproduces the observed wide distribution of isotopic composition suggests the importance of detrained ice in the TTL, as hypothesized from previous work. The results of the model and the observations also illustrate that stratospheric abundances of stable isotopes of water can be understood based on known isotopic physics, convective detrainment of ice and gradual dehydration. 

Gettelman has also been working as part of a team with university collaborators to put isotopes in the NCAR Community Climate System Model. As part of this work, Gettelman and Mahowald coordinated a workshop on “Isotopes in the Earth System” held at NCAR in January 2004.

In collaboration with Paul Konopka of Research Center of Jülich, Germany, Pan has evaluated the application of the Chemical Lagrangian Model of the Stratosphere (CLaMS) model in the region of the extratropical tropopause. Using a simple initialization of O3 and CO, they have demonstrated the importance of mixing in reproducing observed tracer variability.  Figure 39 demonstrates the successful simulation of mixing for the event shown in Figure 36.  This shows that the observed O3-CO relationship is reproduced when mixing is included in the calculations, whereas under pure advection the tracer relationships cannot be obtained.  A successful simulation of the observed “mixing line” will allow quantification of irreversible UTLS transport.

 

 Figure 39: CLaMS simulation of mixing in the vicinity of the subtropical jet (color points), compared with observations (black points, from Figure 36).  The colors denote the fraction of stratospheric air in each parcel. The left panel shows a simulation with mixing, and the right panel is a simulation with no mixing.

 

 

UTLS Chemistry and Aerosols

Brian Ridley and the AON Group have completed analyses covering two subjects relating to the NO and NOy measurements (made in conjunction with a variety of other gaseous and particulate/ice constituents) obtained from flights of the high altitude NASA WB-57F aircraft during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) project during July 2002. 

The first subject considers the uptake of HNO3 by sulfate aerosols (Figure 40).  In situ measurements revealed near-zero mixing ratios of gas-phase HNO3, in the absence of ice particles, at and just above the tropical tropopause for extended periods of one flight south from Key West, Florida.  These data are unique within CRYSTAL-FACE for having depletion of gas-phase HNO3 not in association with ice particles.  In a collaboration with David Fahey, Ru-Shan Gao, Peter Popp, Tim Marcy (NOAA Aeronomy Lab), Robert Hermann (NASA JPL), Elliot Weinstock (Harvard University), and Darrel Baumgardner (UNAM), the AON Group has interpreted this removal as HNO3 uptake on sulfate aerosols in an ice-supersaturated environment.  Calculations for ternary (H2O, H2SO4, HNO3) liquid solutions can approximately account for the low HNO3 mixing ratios by demonstrating that near complete removal from the gas phase is expected for the observed conditions.  It is possible that a modest amount of NH3 may contribute to the HNO3 uptake.  Nitric acid trihydrate (NAT) equilibrium calculations also yield significant uptake, but the nucleation barrier for NAT makes uptake by liquid solutions more likely, especially in the presence of the large aerosol volume for this case.  This phenomenon may have significance for the subsequent evolution of the reactive nitrogen balance in the air mass, as well as for the potential role of these aerosols as sites for ice nucleation in subsequent cirrus cloud formation.  A manuscript is nearly complete.

Figure 40: Plot of measured gas-phase HNO3 (courtesy of David Fahey et al., NOAA Aeronomy Lab), with near-zero values in periods four and five, along with the calculated uptake of HNO3 by ternary liquid solutions (STS), binary liquid solutions (BS, H2O/HNO3), and NAT.  Ambient temperature is plotted (black), along with the equilibrium threshold temperatures for NAT (red) and NAD (blue).  Although both the STS and NAT equilibrium calculations yield significant uptake, the nucleation barrier for NAT makes uptake by liquid solutions more likely, especially in the presence of the large aerosol volume for this case.  Also, it is possible that a modest amount of NH3 in solution may enhance the HNO3 uptake beyond that calculated here.

The second subject considers the production of NO by lightning as investigated by the aircraft during penetration of the anvils of a large number of different thunderstorms that formed over Florida.  A manuscript has just been published.  Exceptionally high mixing ratios (6-10 ppbv) over large scales (20-50 km) were observed as a result of lightning production, which will have a substantial impact on the photochemical generation of ozone in the downwind outflow altitude range.  Larger scale peak mixing ratios of NO were higher on average than found during an earlier study of thunderstorms over eastern Colorado.  Injection of NO from the storms was overwhelmingly into the upper troposphere and very little, if any, into the stratosphere.  The observations were also compared with the lightning parameterization scheme that is used in the MOZART global chemistry-transport model.  Lesley Ott and Ken Pickering (University of Maryland), Lihua Li, Gerry Heymsfield, and Matt McGill (NASA Goddard), Paul Kucera (University of North Dakota), Louisa Emmons (ACD), and Martin Schultz and Guy Brasseur (Max Planck, Hamburg) contributed greatly to the storm analyses and model comparison.

Mike Coffey and Jim Hannigan of the Optical Techniques (OT) Group, as part of the international Network for the Detection of Stratospheric Change (NDSC), operate an infrared Fourier transform spectrometer (FTS) at Thule, Greenland (76.53°N). The NDSC is a network of high quality ground based observing stations for early measurement of changes in the composition and state of the stratosphere and determination of their causes.   Operation of the spectrometer at Thule is automatic, with monitoring from Boulder, whenever the weather is suitable and the sun is above the horizon.  Observations were made on 75 days of the possible 225 sunlit days of 2004.  Missed days usually are due to stormy weather.  Those data were analyzed for column amounts of gases, including both stratospheric gases important in ozone chemistry and tropospheric gases related to climate change.

In conjunction with other observations from the network, composed mostly of instruments from nations other than the U.S., the OT Thule measurements were used in the validation activities of recently launched satellite-borne instruments. Collaborations are ongoing with instruments aboard the Envisat (ESA) platform; plans and collaborations have been established for validation of the EOS-Aura (U.S., U.K., Netherlands, Finland, Launched July, 2004) satellite-borne instruments.  During March 2004, observations were made in conjunction with measurements by the Atmospheric Chemistry Experiment (ACE) instrument aboard the Canadian SCISAT (Scientific Satellite)-1 satellite.  This was the first opportunity for coincident observations by the ACE FTS and the NCAR FTS since the launch of SCISAT-1 in August 2003.  Coincident observations are critical to the validation of space-borne sensors.  Other coordinated observations will be undertaken as the irregular orbit of SCISAT allows.

Results from observations by the airborne Fourier transform spectrometer (0.06 cm-1 resolution), that span more than 20 years, have been reprocessed to produce a unique archive of observations, from the base of the stratosphere, covering a wide range of latitude and season.  This archive of infrared spectra has been used along with recent advances in least squares fitting in multiple wavelength regions to study the long-term trends in water and its isotopes, OCS and CO.  Water transfer across the tropopause and redistribution in the lower stratosphere are important factors to the chemistry, radiation and dynamics of that important atmospheric transition region.  Variations in the behavior of the water isotopes can provide insight into the sources and distribution of water.

Measurements of organic trace gases and other tracers, such as CO2, N2O, CH4 and water vapor, are among those required to adequately characterize the chemistry of any given stratospheric region and to provide important information to diagnose stratospheric transport processes.  Four complementary observational systems are currently employed to measure these trace gases in the stratosphere and each have their own unique set of advantages.  The four include satellite observations, in situ measurements, remote soundings, and measurements from whole air samples.  Elliot Atlas, Sue Schauffler, Verity Stroud, Rich Lueb, and Amy Lueb of the STM Group have collected and analyzed whole air samples from high altitude aircraft, the NASA ER-2 and WB-57, for a number of years.  The maximum altitude for these aircraft is about 65,000 feet.  Recently the STM Group designed and built a whole air sampler to be flown on a high altitude balloon up to 110,000 feet.  Two test flights were flown, one in October, 2003 and the second in September, 2004, from Ft. Sumner, New Mexico.  Figure 41 shows a vertical profile of methane and nitrous oxide (N2O) from the 2004 flight.  The structure of the profile above about 70,000 feet is similar to that seen in the 2003 flight and the STM Group is currently evaluating potential transport characteristics that my influence the distributions.

Figure 41: Vertical profiles of N2O and CH4 from samples collected by the Cryongenic WAS (CWAS) during the balloon flight from Ft. Sumner, NM in 2004. 

 

An important use of whole air sampler trace gas measurements is to determine temporal trends of mixing ratios in the stratosphere to accurately assess the impact of changes in these gases on stratospheric ozone.  Figure 42 shows a correlation between hydrofluorocarbon (HFC) 134a, which is a replacement for CFC-12, and N2O from the balloon flight in 2004 and a series of ER-2 flights out of northern Sweden in 2000.  The higher 134a mixing ratios in 2004 are a result of increased emissions over time, which leads to increased mixing ratios over time.  The STM Group is continuing analysis of these results for all the major halocarbons. 


Figure 42:  HFC 134a mixing ratios relative to N2O mixing ratios from WAS samples collected on the NASA ER-2 during the SOLVE campaign in 2000 and from CWAS balloon samples collected from Fort Sumner, NM in 2004.  The higher HFC 134a mixing ratios during 2004 relative to 2000 are a result of increasing tropospheric mixing ratios over time due to increasing emissions.  HFC 134a is a replacement compound for CFC-12 in refrigerant applications.

 

Atlas and Schauffler of the STM Group also flew a Whole Air Sampler (WAS) on the WB-57 during the NASA Pre-AVE campaign conducted out of Houston and Costa Rica in January and February 2004.  Pre-AVE was an initial test experiment leading to AVE, scheduled to begin in FY 2005.  The Pre-AVE campaign was designed to test aircraft instruments to ensure their measurements are adequate for Aura validation and to test flight strategies for underflights of Aura during the AVE campaigns.  The science goals of Pre-AVE were to characterize air in the extratropical and tropical upper troposphere and lower stratosphere and to examine water vapor, particles and other gases in the tropics to gain insight into their relationships to climate change.

There were three flights out of Houston, Texas, a transit flight to Costa Rica, three flights out of Costa Rica over the equator, and a transit flight back to Houston.  Up to 50 samples were collected per flight and sent back to NCAR for analysis, by Verity Stroud and Amy Lueb, of halocarbons, hydrocarbons, organic nitrates, CO, and N2O.  These trace gases have different chemical lifetimes and either natural and/or anthropogenic emissions and are used to evaluate source regions, air mass transport, and chemical gradients in the upper troposphere and across the tropical tropopause region.  Additionally, the measurements provide needed information on the role of short-lived halogen compounds to the chemistry of the UTLS, and on the transport of hydrochlorofluorocarbons (HCFCs) and HFCs into the lower stratosphere. 

Though the data are not finalized, some interesting observations during the mission demonstrate the utility of tracer measurements from the whole air sampler in identifying air masses influenced by convection.  The convective transport of tropical air is suggested by the data illustrated in Figure 43 that shows a vertical profile of bromoform and methyl iodide over Houston, Texas.  Bromoform and methyl iodide have significant emissions from mainly biogenic sources in the surface ocean, with strong sources in the tropical ocean.  The profile over Houston shows a clear maximum in bromoform and methyl iodide near 10 km, while dichloromethane (not shown) was closer to a “typical” profile of decreasing mixing ratios with altitude.  The layer near 10 km was therefore associated with relatively recent convective outflow from tropical/marine convection.  The relatively high levels of methyl iodide (a trace gas with a lifetime of only several days) also shows that the convection was recent or the levels would have decayed to near background levels.

Figure 43: Vertical profiles of bromoform and methyl iodide near Houston, TX showing a maximum near 10 km that appears to be associated with relatively recent convective outflow from tropical/marine convection.

 

 

Instrument Development

ACD has been or will develop several instruments for use on the HIAPER GV aircraft.  Four of these, the Trace Organic Gas Analyzer (TOGA), HIAPER Radiation Package (HARP), fast ozone, and CIMS were funded as part of the HIAPER MRE for community instrumentation.

 

Trace Organic Gas Analyzer (TOGA):  Measurements, Standards, and Intercomparisons (MSI) Group

A main goal of the MSI Group’s research activity is to participate in collaborative efforts to quantify the chemical composition of the atmosphere, characterize how it is changing in response to natural and anthropogenic forcings, and, ultimately, develop the capability to predict changes that may have important implications for the health of the Earth’s ecosystem.  An area of MSI expertise is in the development and deployment of instrumentation to measure a suite of volatile organic compounds (non-methane hydrocarbons, oxygenated volatile organic compounds, and CFCs and HCFCs) that directly impact the ozone chemistry of the troposphere/lower stratosphere.  A special emphasis is placed on the interpretation of our measurements with respect to their impact on cycles of NOx, HOx and ClOx.

The MSI Group was awarded funding to design and construct the HIAPER Trace Organic Gas Analyzer (TOGA).  The HIAPER aircraft presents a unique opportunity for the MSI Group to study many atmospheric chemical and dynamical processes that occur in the upper troposphere, lower stratosphere (UTLS) region of the atmosphere, including the exchange between the lower troposphere and the UTLS (particularly convective and frontal transport of reactive organic compounds); the influence of oxygenated compounds on the UTLS HOx budget; the participation of short-lived halogen compounds in ozone destruction cycles; the importance of the UTLS as a location of aerosol formation and modification; and the impact of the upper troposphere as a transport conduit for global anthropogenic pollution. A diagram for the sample flow and detection is shown in Figure 44.


Figure 44: Simplified sample flow and detection for TOGA. SSV = stream selector valve. BPR = back pressure regulator, ZA/DS = zero air/dynamic dilution system, MSD = Agilent 5973 mass spectrometer, ECD = electron capture detector, HID = helium ionization detector.

The TOGA will have the unique capability of simultaneously measuring, with one instrument, a suite of organic compounds that play important functions in many areas of atmospheric chemistry. Several of the compounds are precursors or intermediates in atmospheric oxidation sequences. Others are indicators or tracers of different anthropogenic and biogenic processes. By utilizing a full suite of individual compounds, the Group will be able to investigate important processes that are occurring in the troposphere and the UTLS. The compounds that TOGA will measure consist of a series of hydrocarbons, oxygenated compounds, halocarbons (including HCFCs and CFCs), and a few nitrogen and sulfur containing compounds. These species are identified in the HIAPER Advisory Committee Report as high priority in the research air chemistry instrument needs, and these measurements are possible due to the very recent development of new fast gas chromatographs. A demonstration of the analysis of a series of oxygenated volatile organic compounds (VOCs) is shown in Figure 45. The trace in red shows the temperature program.

Figure 45: Demonstration of chromatography obtained in a recent analysis on the new chromatograph. Analysis to pentanal originally required 3.5 minutes.

 

The TOGA instrument will be an effective tool that can be used in conjunction with other research instruments to understand key processes occurring in the troposphere and UTLS.

 

NO/NOy and O3:  AON Group

A major effort has continued with the design, fabrication, and laboratory testing of components for the NOy/NO instrument to be deployed on HIAPER.  The basic detector module, electronics, data system design and much of the machining have been completed.  Assembly is ongoing and testing will start in December.  The design of inlets and fabrication has yet to be completed. 

The Group, plus Teresa Campos (ACD/EOL-RAF), was successful with a proposal to the HIAPER-MRE funding pool to construct a fast ozone (5 Hz response) instrument.  Initial design, based on instruments we have flown on many other aircraft, has been started.  Both the NO/NOy and O3 instruments will operate autonomously on HIAPER.

 

HIAPER Radiation Package (HARP):  ARIM Group

Rick Shetter and three co-investigators, Barry Lefer (University of Houston after 1 September 2004), Manfred Wendisch (Leibniz Institute for Tropospheric Research, Germany), and Peter Pilewski (CU), collaborated on an NSF-MRE proposal to provide state-of-the-art radiation instrumentation for the HIAPER aircraft.  The ARIM Group will design, fabricate, and deliver down and up-welling wavelength dependent actinic flux spectroradiometers and down and up-welling horizontally stabilized wavelength dependent irradiance spectroradiometers. The actinic flux spectroradiometers will provide actinic flux data from 280 to 680 nm with data frequencies ranging from 0.1 to 10 Hz. The irradiance instruments will provide flat plate irradiance from 300 to 2400 nm with data frequencies of 1 Hz. The irradiance optical collectors will be mounted on actively stabilized platforms to maintain horizontal stability to 0.1 degree up to aircraft pitch and roll angles of 6 degrees. This proposal was selected for funding and work will start in FY05.

 

Development of Autonomous Actinic Flux Instrumentation for High Altitude Aircraft – NASA WB-57

The ARIM Group completed the development and design of two CCD-based Actinic Flux Spectroradiometer (CAFS) instruments to measure the down- and up-welling UV and visible actinic flux as a function of wavelength for the NASA WB-57 aircraft. The instruments were fabricated and will be integrated on the NASA WB-57 aircraft platform for an Aura validation mission in October and November of 2004. The UV actinic flux can be used in conjunction with radiative transfer calculations to obtain ozone column abundances above the aircraft, which will be extremely useful for Aura satellite instrument validation activities. A second part of the proposal is in collaboration with Dr. Irina Petropavlovskikh (CU; NOAA). She will develop algorithms to calculate the ozone column abundances from the UV actinic flux. This will be accomplished by applying radiative transfer calculations to obtain the direct fraction of the measured actinic as a function of wavelength and solving for the ozone absorption. The ozone column data will be extremely useful for the Aura satellite validation activities and for future deployment of actinic flux instrumentation on NSF aircraft.

 

Chemical Ionization Mass Spectrometer (CIMS): LK Group in Collaboration with Georgia Institute Of Technology

A CIMS capable of measurements in two basic configurations will be constructed for HIAPER in collaboration with Greg Huey (GIT). In one configuration the instrument will measure nitric acid, pernitric acid, and sulfur dioxide in real time. Other species such as chlorine nitrate and dinitrogen pentoxide may be available after post-flight data processing.  The second configuration will allow measurements of organic compounds such as methanol, acetaldehyde, and acetone.  Data will be reported from one to three second time intervals.

 

Development of a prototype HIAPER OH instrument

A new, compact mass spectrometer instrument has been designed and built by the POP Group (Fred Eisele, Lee Mauldin, and Ed Kosciuch) this past year in order to allow OH to be measured on a Twin Otter aircraft during the upcoming ANTCI 2005 study.  This instrument, when complete, should be four to five times smaller and lighter than the existing four-channel system but still provide similar sensitivity for measuring OH, H2SO4 and MSA.  The new system makes use of advances in mass spectrometer and octopole lens design and will serve as a prototype for a future HIAPER OH instrument.

 

Fourier-Transform Infrared (FTIR) Spectrometer for HIAPER

The OT Group (Mike Coffey and Jim Hannigan) has developed a compact (within the limits of long internal path length) high resolution (0.003 cm-1) Fourier transform spectrometer for use aboard the new NCAR research aircraft, HIAPER.  The optics and mechanical components of that instrument were completed and tested in 2004; electronics are in production.

 

Research Groups

Atmospheric Odd Nitrogen (AON)

Atmospheric Radiation Investigation and Measurement (ARIM)

Measurement, Standards, and Intercomparisons (MSI)

Optical Techniques (OT)

Stratospheric/Tropospheric Measurements (ST/M)

The Satellite Data Analysis (SDA)

The High Resolution Dynamics Limb Sounder (HIRDLS)

 

Middle Atmosphere Science

WACCM was developed to study middle atmosphere physical and chemical processes.  Members of the WACCM Group include Rolando Garcia, Doug Kinnison, Daniel Marsh, and Stacy Walters in collaboration with Byron Boville and Fabrizio Sassi (CGD), and Raymond Roble, Benjamin Foster, and Qian Wu (NCAR’s High Altitude Observatory [HAO]).  WACCM is still under development; however, WACCM simulations have been used in a variety of middle atmosphere studies.  Mesospheric processes have also been examined by ACD scientists using a combination of observations and modeling. 

 

Whole Atmosphere Community Climate Model – Model Development and Results

Impacts of El Niño-Southern Oscillation (ENSO) on the Middle Atmosphere

 

(Fabrizio Sassi [CGD], Douglas Kinnison [ACD], Byron Boville [CGD], Rolando Garcia [ACD], and Raymond Roble [HAO])

WACCM was used to study the response of the middle atmosphere to ENSO.  The model was forced with observed sea surface temperature (SST) for the period 1950–2000. Circulation and temperature anomalies associated with ENSO have the structure of vertically-propagating planetary waves that extend from the troposphere to the mesosphere.  In addition, there are anomalies in the zonal mean winds accompanied by large temperature anomalies of opposite sign in the stratosphere and mesosphere; the former being warmer and the latter colder during El Niño events. Near the summer mesopause, changes in momentum deposition by parameterized gravity waves results in warming during El Niño.  Detailed statistical analysis shows that the wavelike response to ENSO is significant throughout the middle atmosphere and even in the troposphere; zonal mean anomalies associated with ENSO are significant in early and late winter in the middle atmosphere (Figure 46).  A chemical/transport simulation was carried out using output from this WACCM run. It shows that when the lower stratosphere is colder (as during La Niña events), some ozone depletion takes place in Northern Hemisphere winter. Conversely, when the lower stratosphere is warmer and more disturbed, as is the case during El Niño events, heterogeneous chemical processes are inhibited (Sassi et al., 2004).

Figure 46: El Niño minus La Niña zonal mean temperature anomalies (K) during (a) December, (b) January, (c) February, and (d) March. Contour interval is 1 K. Shading indicates anomalies that are significant at least at a 95% level according to the Monte Carlo test.

Seasonal Variability of Trace Species in the UTLS Region

(Mijeong Park [Seoul National University], Douglas Kinnison [ACD], Byron Boville [ACD], Rolando Garcia [ACD], Wan Choi [Seoul National University])

Seasonal variations of several trace constituents (methane, water vapor, and nitrogen oxides) derived from the Halogen Occultation Experiment (HALOE) satellite observations near the tropopause were analyzed and compared to output from the MOZART-3 chemistry-transport model driven by WACCM dynamics. These species have strong gradients near the tropopause, so that their seasonality is indicative of stratosphere/troposphere exchange (STE) and circulation in the near-tropopause region.  Results show good agreement between observations and model simulations for methane and water vapor (Figure 47), whereas nitrogen oxides near the tropopause are much lower in the model than suggested by HALOE data. The latter difference is probably related to the lightning and convective parameterizations incorporated in MOZART-3, which produce NOx maxima not near the tropopause, but in the upper troposphere. Constituent seasonal variations highlight the importance of the Northern Hemisphere (NH) summer monsoons as regions for transport into the lowermost stratosphere. In MOZART, there is clear evidence that air from the monsoon region is transported into the Tropics and entrained into the upward Brewer-Dobson circulation, bypassing the tropical tropopause (Park et al., J. Geophys. Res. 2004).

Figure 47: Meridional cross sections of water vapor mixing ratio in the South Asian monsoon region (60_–120_E) in July. Results are shown for (a) HALOE observations and (b) MOZART simulation. The heavy dashed lines indicate the tropopause appropriate for each data set.

 

Stratospheric Influence on Seasonal Cycles of Tropospheric Tracers

(Cynthia Nevison [ACD], Douglas Kinnison [ACD], Raymond Weiss [Scripps Institution of Oceanography])

The stratospheric influence on the tropospheric seasonal cycles of N2O, CFC-11 (CCl3F), CFC-12 (CCl2F2) and CFC-113 (CCl2FCClF2) was investigated using observations from NASA’s Advanced Global Atmospheric Gases Experiment (AGAGE) global trace gas monitoring network and the results of WACCM simulations.  WACCM provides the basis for a number of predictions about the relative amplitudes of N2O and CFC seasonal cycles and about the relative magnitude and phasing of seasonal cycles in the Northern and Southern Hemispheres.  These predictions are generally consistent with observations (Figure 48), suggesting that the stratosphere does exert a coherent influence on the tropospheric seasonal cycles of trace gases whose primary sinks are in the stratosphere.  This stratospheric influence may complicate efforts to validate estimated source distributions of N2O, an important greenhouse gas, in atmospheric transport model studies. (Nevison et al., in press).

Figure 48:  Comparison of modeled vs. observed seasonal cycles.  Dotted lines are WACCM 700mb CFC-11 (red) and CFC-12 (black) seasonal cycles.  Solid lines are AGAGE observations  a) Mace Head, b) Trinidad Head.

 

Monsoon Impacts on Stratosphere/Troposphere Exchange (STE)

(Andrew Gettelman [ACD/CGD], Kinnison [ACD], Timothy J. Dunkerton [North West Research Associates], and Guy Brasseur [Max Planck Institute, Hamburg])

Using observations from aircraft and global chemical and climate models, the transport characteristics of the Asian monsoon complex on the upper troposphere and lower stratosphere have been examined in detail. A long-term WACCM climatology resembles the satellite climatology of water vapor and ozone in the monsoon regions (Figure 49).  A simulation with observed winds is able to reproduce individual transport events observed from aircraft, and these events are used to infer that large scale motions and monsoon circulations can explain the global correlations of ozone and water vapor around the tropopause.  A detailed analysis of model fluxes of water vapor and ozone indicates that the Asian Monsoon circulation may contribute 75% of the total net upward water vapor flux in the Tropics at tropopause levels from July to September. Some of this air may enter the tropical stratosphere and bypass the tropical tropopause altogether (Gettelman et al., in press).

Figure 49:  Top two panels:  Climatology of water vapor from HALOE at 100hPa and ozone from SAGE at 95hPa.  Bottom two panels:  Climatology of water vapor and ozone from a 22-year MOZART-3 simulation driven with WACCM dynamics. The impact of the Indian monsoon circulation is evident in both data and model.

 

Parameterization of Gravity Wave Fluxes Due to Convective Excitation

(Jadwiga Beres [ASP], Boville [CGD], Garcia [ACD], Sassi [CGD])

A new method of specifying the gravity wave spectrum above convection has been implemented in WACCM. This parameterization is interactive with the underlying convection and introduces realistic spatial and temporal distributions of gravity wave activity as well as yielding gravity wave characteristics related to the underlying wave source. The new scheme improves the structure of the tropical stratospheric and mesospheric Semi-Annual Oscillations in WACCM (Figure 50) and provides insight into the wave motions that might be responsible for extratropical mesospheric forcing. The newly-implemented scheme also provides a new direction for gravity wave parameterizations as the gravity wave forcing is no longer fixed and will follow changes in tropospheric climate. This allows for more accurate studies of effects of changing climate on the middle atmosphere and on examining the feedbacks between the troposphere and the middle atmosphere. (Beres et al., submitted).

Figure 50: Monthly averaged east-west momentum flux phase speed spectra at 100 hPa as a function of latitude derived from the Beres parameterization for a) January, and b) July. Contours are plotted in intervals of 0.25 x 105 kg m-2 s-1. Thick solid line depicts the zonal mean wind at 100 hPa and the dashed line depicts the zonal mean wind at 700 hPa. In panels c) and d) the thick lines depict cross sections through a) and b) respectively at 4°N and15°S. The thin lines depict the same quantity for the standard simulation.

 

Stratospheric Trends in Temperature and Water Vapor

Daniel Marsh [ACD], Garcia [ACD], Kinnison [ACD], and Sassi [CGD]

WACCM/MOZART-3 was driven with observed SST for the period 1950-2000, and the results were compared with satellite and ground-based observations of temperature and water vapor to determine whether the model can reproduce observed trends.  It was found that model results were generally in good agreement with HALOE observations (1992-2002), both for temperature and water vapor.  WACCM tended to underestimate temperature trends only in the upper stratosphere; this discrepancy appears to be related to an underestimate of ozone in that region.  Simulated water vapor trends agreed well with HALOE data throughout the lower and middle stratosphere (Figure 51).  It was also found that the magnitude of trends was highly dependent on the length of the record analyzed, so trends calculated for periods as short as 10 years cannot be considered stable.  Decadal trends appear to be strongly influenced by the presence of low-frequency variability, which in the model arises principally from changes in SST. A paper describing these results is in preparation.

 

Figure 51:  Comparison of WACCM vs. HALOE trends in water vapor.  WACCM reproduces HALOE trends in the lower and middle stratosphere.  HALOE trends are larger in the upper stratosphere, especially in the northern hemisphere.

 

Chemical Transition Across the Extratropical Tropopause

(Laura Pan [ACD], Jennifer Wei [Goddard Space Flight Center], and Kinnison [ACD])

 Distribution of chemical constituents in the extratropical tropopause region is controlled by both chemistry and dynamics.  Correct representation of the chemical distribution and transition across the tropopause is an important diagnosis for the model performance in the upper troposphere and lower stratosphere region.  Large gradients and rapid change in chemical species, especially ozone and water vapor, occur near the extratropical tropopause region making it a significant challenge to models.  This study examined the chemical transition in the extratropical tropopause region in the results of several different model runs in comparisons with the aircraft observations.  Figure 52 is an example of these comparisons.  Both profiles and tracer relationships were examined for runs driven by ECMWF winds, WACCM-1b winds and WACCM2 (interactive chemistry).  The analysis shows that results using ECMWF winds are comparable to observed tracer relationships (O3-CO and O3-H2O).  The results from WACCM-1b show a significant offset between the thermal tropopause and the chemical transition. This Group is in the process of identifying the component in transport characteristics that may be responsible for this offset.  The initial results of examining the WACCM2 show good agreement with the observations. These results are being prepared for publication.

Figure 52:  Comparisons of tracer relationship between model results and aircraft observations.  The two colors represent data (both model and measurements) above (red) and below (green) the thermal tropopause. Note the 65N and 40N show different characteristics in the transition region. Model results are consistent with the observations.

 

Structure and Variability of the SE Asia Monsoon System

(Park [Seoul National University], Randel [ACD], Kinnison [ACD], Garcia [ACD])

Satellite measurements of UTLS ozone and water vapor from the Atmospheric Infrared Sounder (AIRS), along with output from WACCM2, are being used to understand stratosphere-troposphere coupling associated with the monsoon circulations.  Results from WACCM2 and AIRS (Figure 53) reveal consistent patterns of relatively high water vapor and low ozone within the monsoon anti-cyclone during summer. The synoptic patterns from AIRS water vapor and ozone show both the eastward and westward moving wavelike patterns in northern and southern part of the monsoon anticyclone, respectively. Variations in convective activity with 10-20 day periods are associated with fluctuations in anti-cyclone intensity and structure, as quantified using derived potential vorticity (PV) fields.  Consistent patterns are observed in PV, water vapor and ozone, as shown. Analyses of observations and model results will be aimed at quantification of monsoon effects on stratosphere-troposphere exchange. This study is currently underway. 

Figure 53:  Top panel shows spatial structure of UTLS South Asian monsoon region on August 3, 2003, based on PV on the 357 K isentropic level (≈14 km). The relatively low PV region over South Asia (blue region) corresponds to the monsoon anti-cyclone. Lower panels show corresponding water vapor and ozone patterns, derived from AIRS data. Note that relatively high water vapor and low ozone are observed within the anti-cyclone.

 

Mesospheric Processes

Chemistry of the Middle Atmosphere Sodium Layer

Anne Smith, in collaboration with Jiyao Xu (Chinese Academy of Science), has done several studies related to the chemistry and remote sensing of sodium in the middle atmosphere. In one, A. Smith and Xu used a numerical model of sodium chemistry to examine the sensitivity of sodium chemical lifetime to various environmental factors (e.g., temperature and the concentrations of other reactive gases). The paper also predicts a day/night difference in the sodium chemistry. Xu and A. Smith also collaborated with Qian Wu (HAO) to propose a technique for global observations of nighttime sodium by satellite. At present, there are only limited sodium observations from a few lidar sites. This paper demonstrates that determination of the global sodium distribution from satellite is straightforward and can be done with good accuracy. The measurements would require simultaneous limb measurements of temperature, ozone and sodium airglow emission at altitudes around 80-100 km. Such measurements have all been made separately and are technically feasible.

 

Atmospheric Tides

A. Smith, in collaboration with Dora Pancheva and Nicholas Mitchell (University of Bath, U.K.) have completed a comprehensive study of the 6-hour tidal oscillation. Although occasional observations of this tidal frequency have been reported through the years, it had never been the subject of an in-depth study. Smith, Pancheva, and Mitchell found that this tidal frequency is a persistent feature of the variability in winds at the Esrange radar station (Sweden). Model simulations reproduce the mean amplitude and seasonal cycle. The model also predicts the global structure. The prediction gives largest amplitudes at high latitudes and indicates that the tide at a given site is composed of migrating and non-migrating contributions.

 

Oxygen – Hydrogen Chemistry and Emissions in the Mesosphere

Marsh and Smith, in collaboration with Martin Mlynczak (NASA Langley) and James Russell (Hampton University), are using a numerical model to interpret observations of hydroxyl airglow made by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on the TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite. They have found that variations in the airglow are strongly affected by the diurnal tide. Two processes contribute: a) downward vertical motion transports enhanced atomic oxygen which, through a series of chemical reactions, leads to enhanced airglow; and b) the airglow responds to temperature variations because of the temperature dependence of some key reaction rates. Both of these processes play a role in the observed and simulated variability of the emission. Since the chemical reactions that lead to the emission are known, the airglow variations can lead to greater understanding of the composition and its variability.

 

High-Resolution Dynamics Limb Sounder

HIRDLS was launched on the Aura spacecraft on 15 July 2004 (Figure 54), 16 years to the day from the submission of the original proposal.  Here activities will be divided into pre- and post launch phases.

 

Figure 54: (Credit and copyright (c)  Brian Lockett, Goleta Air & Space Museum) NASA's AURA satellite launched from Vandenberg AFB at 3:02 A.M on Thursday, July 15. It will examine the Earth's atmosphere in unprecedented detail.

 

Pre-launch Activities

Instrument

At the beginning of the period, HIRDLS had been integrated on the Aura spacecraft (S/C), which was about to be tested under the thermal and vacuum (T/V) conditions that it would experience in space.  Many members of the HIRDLS Team took part in the month of T/V testing, including John Gille (ACD; CU), Michael Coffey, Bruno Nardi, Thomas Eden, and Michael Dials, Douglas Woodard, and Aaron Lee (CU).  An earlier increase in radiometric noise was finally traced to a beating between the chopper frequency and the 13th harmonic of the cooler frequency.  Raising the chopper frequency moved this interference out of the range of concern.  However, the noise was related to the failure of one of the four cooler motors.  During the subsequent T/V testing another section of the cooler electronics failed, limiting the amount of radiometric testing that could be done.  After a considerable amount of trouble-shooting, analysis, and reworking of the electronics, the instrument was declared ready to fly, although there were some remaining questions.  All tests completed before the cooler failure showed continued excellent performance. 

Further testing and flight simulation, led by James Craft and Angela Williams (CU) took place at the S/C integration site in Redondo Beach, CA, before Aura was shipped to the launch site at Vandenberg Air Force Base, on the Pacific coast north of Santa Barbara.  After delays of a few weeks due to launcher problems, Aura was launched flawlessly into a sky clear enough that the rocket plume could be seen for a hundred miles or more.

Closely related to this, Eden worked to complete the final data analyses of the radiometric and in–band spectral data sets from the pre–launch calibration, which had taken place the previous year in Oxford.  He subsequently assisted in the inclusion and testing of these results in the relevant science–data processing algorithms.

In response to the possibility of a malfunction in the in-flight calibrator (IFC) temperature sensors raised during the instrument calibration phase, Alyn Lambert added the capability of simultaneously retrieving the IFC temperature and atmospheric temperature/pressure to the Level-2 operational software and showed that the scientific goals of the HIRDLS mission could still be achieved.

 

Algorithm Development

Lambert and Hyunah Lee completed work on the operational Level 2 (L2) algorithms to convert the measured radiances into atmospheric data.  They implemented and tested them in the operational environment, showing that they met the data requirements.  They also developed a HIRDLS test suite, consisting of a series of four increasingly complex retrieval paths, to help plan and guide the retrieval of HIRDLS products through the early post-launch data. 

Charles Cavanaugh developed software to provide the calibrated radiances (L1) needed by the L2 algorithms, while Lawrence Lyjak, William Mankin (retired), Gille and Brent Petersen (CU) created the pre-processor link between L1 and L2 that, inter alia, enhanced the vertical resolution of the retrieved products. 

Ken Stone (CU) led the effort to develop a very powerful and flexible automated data processing system, with the help of Thomas Lauren, Greg Young and Vince Dean (CU). Cheryl Craig, worked with Charles Krinsky and Joe McInerny (CU), to develop the operational code. 

Lambert and Lee also generated 24 hours of HIRDLS simulated data (radiances and retrieved products) from 4D Mozart model data supplied by Douglas Kinnison which was used in pre-launch inter-comparison and validation exercises by the HIRDLS and Microwave Limb Sounder (MLS) science teams.

In closely related work, Rashid Khosravi developed and implemented two new run modes in the retrieval code for error analysis and diagnostic purposes. One mode calculates the averaging kernels and various components of the total retrieval error, and the other mode calculates weighting functions by a finite difference method.  He also analyzed the constituent mixing ratio errors resulting from errors in retrieved temperatures, and a priori errors.

The L2 algorithms require a forward model that must accurately and quickly estimate transmittances and channel radiances for use in the operational retrievals. It must take into account the presence of many target and interfering gases, a wide range of atmospheric and radiative states, operational speed constraints, and requirements on the accuracy and precision of the retrieved science data. Significant progress has been made in addressing these challenges. Gene Francis and David Edwards successfully extended a physically based forward model framework to a fast regression approach incorporating improved spectroscopy that is effective for operational use. Francis, Julia Lee-Taylor, Chris Halvorson and Lambert have tested it using 11 diverse atmospheres, ranging from tropical to winter polar conditions, based on MOZART data. Radiance errors are deviations from a line-by-line reference. Accuracy is generally better than 0.5% and satisfies the operational requirement of < 0.5%-1.0% depending on channel. Radiance accuracy is considerably better than 0.5% for the critical temperature retrievals obtained with the CO2 channels.

Kinnison, Nardi, Gille and Cora Randel (CU) led the HIRDLS planning for data validation. 

Plans were also made to use HIRDLS data in the UT/LS initiative led by ACD.  Figure 55, prepared by Lambert, presents maps of simulated HIRDLS retrievals of ozone data on 3 isentropic surfaces in the UT/LS.  The violet indicates low tropospheric ozone values in the tropics, with sharp gradients to higher low stratospheric values.  The wavy isolines follow the PV tropopause more or less. Motions on isentropic surfaces across the tropopause are expected to be a major mode of Strat-Trop exchange.  (HIRDLS data will extend only down to the cloud tops.)

 

Figure 55:  Maps of simulated HIRDLS ozone data on three isentropic surfaces in the Upper Troposphere/Lower Stratosphere (UTLS).

Post-Launch Activities

Once in orbit, the HIRDLS Flight Operations team led by Craft and Williams worked with our colleagues at Oxford University, especially John Barnett and Chris Hepplewhite, to implement the instrument activation plan, which turned on the subsystems one at a time and evaluated them before going to the next step.  This also allowed HIRDLS and the S/C to outgas for 25 days.  The coolers were slowly turned on without problems and allowed to cool down on 10 August.  When the detectors stabilized at their operating temperature (61.6K), the scanner was programmed to obtain 15 minutes atmospheric observations. 

The results of these scans were quite surprising and disappointing.  The observed radiances were much larger and more uniform spatially and spectrally than atmospheric radiances. The immediate impression was of an obstruction in front of the instrument aperture. In addition, a few days earlier it had been noted that the scanner was not moving as freely as it had on the ground.

NASA immediately formed two review groups to help guide the investigation of the radiance anomaly, and its possible link with the scanner interference.  Further scanner motion was barred for the near term. The first tasks were to list all possible causes of the observed anomaly, and then use all available data to narrow the range of possible causes.  Most of the above-mentioned team members have played active roles in this.  By the end of FY04 an obstruction in the optical train was identified as the most likely cause, and all other mechanisms were on the verge of being formally ruled out.  The obstruction is now believed to be a piece of kapton, the plastic sheeting placed around the fore-optics volume to maintain cleanliness, that came loose during the rapid de-pressurization at launch.  Present plans are to do further diagnostic motions of the scan mirror, measuring both radiances and drag on the mirror, to get a better understanding of the location of the blockage, then develop a plan for moving it out of the way.  Should this fail, the fallback position is to see whether data measured at one end of the aperture, where there is a partial view past the blockage to the atmosphere, can yield useful scientific results.

 

Research Groups

Global Modeling (GM)

The High Resolution Dynamics Limb Sounder (HIRDLS)

Optical Techniques (OT)

 


Strategic Initiatives

 

Biogeosciences Strategic Initiative

 

Executive Summary

 

The Biogeosciences Initiative science agenda is organized around issues linking processes across spatial scales. An explicit element of our plan is to use numerical modeling at multiple scales to integrate a wide range of observations. Our approach is based on the recognition that physical and biological processes operating at very small spatial scales have the potential to influence the climate system when integrated globally. It is therefore imperative that we develop a set of diagnostic and prognostic tools that can seamlessly span the spatial scales from single organisms to the entire globe, making optimal use of the observations possible at different scales. For example, the performance of the global land carbon cycle model is being evaluated against global-scale observations of CO2 concentration, against continental-scale observations of canopy structure from remote sensing platforms, against regional-scale observations of hydrologic outflow, against eddy covariance observations of local carbon, water, and energy fluxes, and against very detailed ecophysiological and biometric observations at the stand and plant scales. This becomes increasingly important as we begin to address human impacts on the global biogeochemical environment and climate system.

The Biogeosciences (BGS) mission encompasses four main tasks:

  1. Global Modeling and Measurements: Investigate biogeochemical coupling to radiative forcing, climate air quality, and ecosystem function on continental to global scales.
  2. Regional Air Quality and Chemical Processes: Link process level biogeochemical understanding to regional-scale measurements and models.
  3. Models and Measurements over Heterogeneous and Complex Terrain: Understand how complex terrestrial landscapes interact with physical processes in the atmosphere to influence biogeochemical and physical ecosystem processes, land-atmosphere exchange, and local climate.
  4. Land Use Changes: Investigate how human driven changes in land use affect biogeochemical cycles.

These tasks are shared across four divisions, ACD, ATD, CGD and MMM.

 

BGS Achievements (Division Narratives):

 

Atmospheric Chemistry Division: ACD

The Atmospheric Chemistry Division (ACD) has a mission goal of advancing our understanding of the role of biosphere-atmosphere interactions in the Earth system and predicting its response to human perturbations. This is being accomplished through multidisciplinary field, laboratory and modeling studies of the processes controlling these interactions at a variety of scales. These studies mainly contribute to BGS Tasks 1 (process and regional scales), with some topics also contributing to Task 2 (global scale).

The BGS initiative contributed during FY04 to the support of Global Modeling Section (GMS) member Elisabeth Holland, and Biosphere-Atmosphere Interactions (BAI) Group members Andrew Turnipseed and Christine Wiedinmyer. Holland is the BGS Program Leader, and Alex Guenther (ACD-BAI) is a BGS Steering Committee member.

Carbon-Nitrogen Cycling (Tasks 1 & 2)

Holland collaborated with Bobby Braswell (University of New Hampshire), James Sulzman and Jean-Francois Lamarque (ACD-GMS) to produce maps of N deposition fluxes from site-network observations for the United States and Western Europe (Figure 56) and to construct continental- scale N budgets.

 

 

Figure 56: Nitrogen deposition to Western Europe exceeds that to the US:. Nitrogen is being exported from the US.

 

The U.S. N deposition budget is found to be dominated by oxidized N species, byproducts of fossil-fuel combustion, while the Western European N-deposition budget is dominated by reduced species, by-products of farming and animal husbandry. Western Europe receives 5 times more N in precipitation than the conterminous U.S. Estimated N emissions greatly exceed measured deposition in the U.S., suggesting significant N export or under-sampling of urban influence. In Europe, estimated emissions better balance measured deposition, suggesting that much of the N emitted in Europe is re-deposited there, with possible N import from the U.S. These wet and dry N flux maps are valuable as input into terrestrial biogeochemistry models and for verification of regional and global atmospheric chemistry and transport models. The work is detailed in a paper in press (Holland et al). The data set used for the synsthesis has been published separately through the Oak Ridge National Laboratory Data and Archiving Center (ORNL-DAAC), url: http://daac.ornl.gov/CLIMATE/guides/nitrogen_deposition.html

Holland also collaborated with Wolfgang Knorr, Jo House (Max Planck Institute for Biogeochemistry, Jena, Germany) and Colin Prentice (University of Bristol, UK) in a study which answers a controversy as to whether turnover of soil organic carbon (SOC) has any long-term temperature sensitivity. A 3-pool model (Figure 57) was used to explain that labile SOC undergoes rapid depletion on warming, whereas non-labile SOC shows negligible response on experimental time scales, but is actually more sensitive than labile SOC to temperature in the longer term. These results imply that the long-term positive feedback of soil decomposition in a warming world may be even stronger than predicted by global models. A paper (Knorr et al) is in press in Nature.

 

Figure 57: Temperature responses of the 3-pool Arrhenius model. (a) Turnover times of the three pools as a function of temperature (thick lines): fast (light grey), intermediate (medium grey) and slow (black). The dotted black line uses the best fit value for activation energy (Table 1b), the solid line 68,000 J mol-1 as a lower bound. The uppermost line shows turnover times calculated with the method of ref. 24. (b) Modelled response of the pool sizes to a 2°C warming (grey tones as (a)). (c) Modelled temperature response of CO2 efflux after warming the soil by 2°C for 1 month (dashed) or 1 year (dotted), compared to the temperature response without warming (solid).

 

BGS provided inspiration for the "Santa Fe Project", a study by Lamarque of nitrogen deposition on the biosphere and its impact on the carbon cycle. BGS continues to cooperate with the ongoing efforts of the Santa Fe Project. More detail can be found on the ACD website, url: http://www.acd.ucar.edu/chemistry_climate

The remaining portion of the ACD contribution is taken from the above Biogeochemical Cycles section and reflects the figure numbering from that section.

Laboratory Studies (Task 2)

Guenther and other ACD-BAI scientists (James Greenberg, Peter Harley, and Thomas Karl) are using laboratory facilities to characterize the processes that control biogenic emissions. Biogenic emission studies were conducted in the ACD phytotron and growth chamber facilities in collaboration with Emiliano Pegoraro (Edinburgh University, U.K.), Allison Steiner (University of California, Berkeley) and Teresa Nunes (University of Aviero, Portugal). The laboratory studies have shown that isoprene emission is more resistant and recovers more quickly from drought than does photosynthesis and stomatal conductance. Isoprene emission rates show a strong correlation with leaf water potential, providing a useful parameterization for including the effects of drought stress in isoprene emission models. Other experiments have demonstrated that sesquiterpene emission rates from some important tree species are comparable to monoterpene emission rates and exhibit similar temperature dependence. Biogenic methanol emission rates were observed to vary across and within plant species by at least an order of magnitude. Leaf age was identified as the major source of within species variation in methanol emission. Observed light dependent monoterpene emissions varied as a function of growth temperature and certain monoterpenes (e.g., ocimene) were released at elevated levels in response to temperature stress. This work is described by Pegoraro et al., Harley et al., and Nunes et al., which are in preparation for submission to peer-reviewed journals in late 2004.

U.S. Field Studies (Task 2)

BAI scientists investigated biosphere-atmosphere interactions with six U.S. field studies during FY04 and analyzed data from an additional three U.S. field studies. The six FY04 field studies supported the research of investigators from five universities. A study of the contribution of biogenic isoprene emission to regional aerosol and oxidants was conducted at a poplar plantation in northern Oregon and was conducted in collaboration with Brian Lamb, Halvor Westberg and Adam Hill (Washington State University). The potential allelopathic role of biogenic VOC emissions from invasive Artemesia shrubs in New York was conducted in collaboration with Jed Sparks and Jacob Barney (Cornell University). An aircraft investigation of cicada outbreaks in Indiana was conducted in collaboration with Paul Shepson (Purdue University) and showed that the emissions from decaying cicadas did not have a significant impact on atmospheric chemical composition. Trace gas fluxes over a Colorado grassland were measured in collaboration with Matt Dunn (ASP/University of Colorado) and James Smith (ACD). The observations show that the grassland was a significant source of methanol and a sink for acetic acid and methyl acetate. Ozone deposition was measured at the Niwot Ridge, Colorado AMERIFLUX site in collaboration with Russell Monson (University of Colorado). The negative impact of high O3 events on the subalpine forests downwind of Denver, Colorado are minimized by their occurrence during late afternoon-early evening periods when plant activity is low due to both water stress and low light levels. Studies of ammonia fluxes from soybean fields in North Carolina were conducted in collaboration with John Walker (North Carolina State University and United States Environmental Protection Agency [USEPA]). Significant fluxes were observed and the results demonstrated the utility of the ammonia CIMS system designed and built by ACD.

FY04 efforts also included a workshop, database development, data analysis and manuscript preparation associated with the Chemical Emissions, Losses, Transformations and Interactions with Canopies (CELTIC) study in Duke Forest, North Carolina led by BAI in collaboration with Chris Geron, Bob Arnts (USEPA) , Walker, Jose Jimenez, Darin Toohey, Alice Delia (University of Colorado), Sparks (Cornell), Mark Potosnak (Desert Research Institute), Greg Huey, David Tanner, Darlene Slusher and Robert Stickel (Georgia Institute of Technology), Kolby Jardine and Bradly Baker (South Dakota Institute of Mining and Technology), Jose Fuentes (University of Virginia) Will Vizuete (University of Texas), Fred Mowry and Jeff Herrick (Duke University), Francesca Rapparini (Istituto di Biometeorologia, Italy), and Rei Rasmussen (Oregon Graduate Institute). The CELTIC results indicate that isoprene emission increases with elevated ozone and, on a canopy scale, with elevated CO2. Future changes in ozone and CO2 could thus change regional isoprene emission rates leading to feedbacks. The pine plantation forest floor (soil and leaf litter) was a significant sink of methanol, acetone, acetaldehyde and isoprene. This is not well represented in existing models and could lead to overestimated ambient concentrations. Substantial sesquiterpene emissions observed from pine trees could be the dominant source of biogenic secondary organic aerosol mass under certain environmental conditions. PAN (and PAN-like compounds) were deposited at a much faster rate than is predicted by current models by a factor of 3-5. This has significant implications for the lifetime of PAN in the atmosphere and its role as a transporter of reactive nitrogen in the atmosphere. Simultaneous observations of biogenic VOC and total organic aerosol during CELTIC allowed new constraints on aerosol yields and OH formation due to ozonolysis. The average aerosol yield for alpha-pinene, beta-pinene and d-carene are higher than calculated, supporting recent laboratory studies showing that polymerization reactions could enhance aerosol partitioning (Figure 29). Based on observed isoprene decay within the canopy, the upper limit of nighttime OH mixing ratios is less than reported measurements for other forests. Estimates of biogenic contributions to secondary organic aerosol mass at Duke Forest suggest that biogenic sources dominate which is somewhat surprising for this moderately polluted site.

Figure 29: Comparison of SOA growth between different modeling approaches compared to measured gradients (red circles).

 

Analysis and publication of two other previous U.S. studies were completed in FY04. A tower flux study of isoprene and oxygenated VOC emissions from a northern Michigan deciduous forest was conducted in collaboration with Raymond Fall (University of Colorado) and Armin Hansel (University Innsbruck, Austria). The differences can be explained by the different physiological and phenological processes controlling these emissions. The multiscale (enclosures, tower, tethered balloon, aircraft) Ozarks Isoprene Experiment (OZIE) study was conducted in collaboration with Brian Lamb and Halvor Westberg (Washington State University), Jay Turner (Washington University), Paul Palmer (Harvard University), Geron and Thomas Pierce (USEPA) and demonstrated that central U.S. oak forests and woodlands have very high isoprene emission rates resulting in elevated regional formaldehyde concentrations. This formaldehyde is often transported northward and eastward towards urban centers such as St. Louis and Chicago, and participates in the production of ozone (Figure 30). Current photochemical models underpredict the magnitude of formaldehyde produced by isoprene oxidation which leads to incorrect chemistry simulations within the urban centers.

Figure 30: Hourly-averaged formaldehyde concentrations for 06:00 CDT on July 21, 1998, as modeled by CAMx. Winds on this day were predominantly from the south-southwest. A plume of elevated formaldehyde can be seen being transported from the forests of the Ozarks towards the northeast and into the Chicago urban area. The majority of this formaldehyde has been formed from the photooxidation of isoprene emitted from the Oak forests of the Ozarks on July 20.

 

International Field Studies (Task 2)

BAI scientists participated in international investigations of biosphere-atmosphere interactions in Brazil, Ireland, and Japan during FY04 and analyzed results from previous studies in China, Costa Rica, Brazil, and Finland. Background measurements were made at a primary tropical forest flux tower near Manaus, Brazil in collaboration with Potosnak, Artaxo, Julio Tota and Antonio Manzi (Brazilian National Institute of Amazon Research [INPA], Brazil). Significant flux of monoterpenes was estimated from the vertical profile shown in Figure 31. The contribution of semi-volatile organic gases to secondary organic aerosol mass was studied in Japan in collaboration with Yoshizumi Kajii (Tokyo Metropolitan University). The results indicate that humidity plays a significant role in determining the uptake of some semi-volatile compounds.


Figure 31: Altitude profile of monoterpenes above the Z34 tower close to Manaus.

 

BAI scientists participating in the BIOFLUX field study on the Irish coast investigated biogenic fluxes of organic iodide compounds in collaboration with Colin O’Dowd (National University of Ireland), Liisa Pirjola (University of Helsinki, Finland) and Thorsten Hoffman (Institute of Spectrochemistry and Applied Spectroscopy [ISAS], Dortmund, Germany). A tethered balloon system was used to characterize vertical gradients of several alkyl halides including di-iodomethane, ethyl bromide and ethyl iodide. Concentrations decreased with height indicating a surface source of these compounds which are believed to be involved in new particle formation.

Two manuscripts were published in FY04 (Spirig et al., and Boy et al.) describing BAI results from the Origins of Secondary Organic Aerosol (OSOA) study that was conducted at a boreal forest site in Finland in collaboration with Christoph Spirig (Swiss Federal Institute of Technology [ETH] Zurich, Switzerland), Michael Boy and Markku Kulmala (University Helsinki, Finland). Total monoterpene oxidation rates during the OSOA study were not correlated with particle production events, but there was a strong correlation with ozone indicating that more ozone reactive biogenic compounds, such as sesquiterpenes, may make an important contribution. Vertical gradients of particles above the forest suggest that particle growth occurs throughout the boundary layer.

Tropical forest biogenic emissions were studied in the eastern Amazon (Brazil) in collaboration with Luciana Vanni Gatti and Carla Trostdorf (Energy and Nuclear Research Institue [IPEN], Brazil) and in Costa Rica in collaboration with Deborah Clark (University of Missouri), Sparks, and Potosnak. Seasonal isoprene variations in the Amazon were much higher than expected (more than a factor of 3 higher in the dry season). Tropical forest ecosystems in both Brazil and Costa Rica were both a significant source (daytime) and sink (nighttime) of methanol, acetone, and acetaldehyde. Dry deposition velocities of these and other (e.g., methyl vinyl ketone, methacrolein, and acetonitrile) compounds were a factor of 10-20 higher than estimated from existing deposition models which has important implications for regional and global chemistry and transport models. This work is described in Greenberg et al., 2004; Harley et al., 2004; Trostdorf et al., 2004; and Karl et al., 2004.

Studies of the impact of land cover change on biogenic emissions from Chinese landscapes were conducted in collaboration with Baker, Rassmussen, Bai Jianhui (Institute of Atmospheric Physics [IAP] Chinese Academy of Sciences), Susan Owen (Lancaster University), and Geron. Chinese rubber tree and oil palm plantations have much higher terpenoid emissions than native tropical forests. This suggests that there has been and continues to be significant increases in biogenic VOC emissions in some tropical regions of China. Severe drought results in a dramatic reduction in these emissions demonstrating the equally important role of climate change. These results are described in Baker et al., 2004; and in two manuscripts in preparation.

Regional Modeling Studies, U.S. (Task 2)

Wiedinmyer and Guenther investigated biosphere-atmosphere interactions in the U.S. using regional chemistry and transport models. FY04 studies included an investigation of the impact of future climate and land cover on regional air quality in the Pacific Northwest and north central U.S. in collaboration with Brian Lamb (Washington State University), Cliff Mass (University of Washington) and Susan Fergusen (U.S. Forest Service) and a study of the contribution of sesquiterpenes and other biogenic VOC emissions to secondary organic aerosols in the eastern U.S. in collaboration with Jana Milford (University of Colorado). Both of these projects were initiated in FY04, and efforts were directed at setting up the regional air quality modeling system and developing the emission scenarios.

Regional Modeling Studies, International (Task 2)

Wiedinmyer, Sreela Nandi (ASP/ACD Postdoctoral Fellow), and Guenther investigated biosphere-atmosphere interactions in China, Brazil, and Mexico using regional chemistry and transport models in FY04. The contribution of biogenic VOC emissions to oxidant and particle production in China was studied in collaboration with Xiaoping Wang and Denise Mauzerall (Princeton University). The results indicate that future growth in China’s fossil fuel emissions will lead to costly decreases in public health and crop productivity. Much of this region is VOC-limited so changes in biogenic VOC emissions will have important consequences for air quality. The BAI Group also supported regional simulations of air quality in Mexico in preparation for the NCAR-ACD Megacity Impacts on Regional and Global Environments [MIRAGE] study (Xuexie Tie, ACD).

Global Modeling Studies (Task 1)

Wiedinmyer and Guenther investigated global scale biosphere-atmosphere interactions in FY04 using global chemistry and transport models. The contribution of biogenic VOC emissions to global organic aerosol was examined in collaboration with Joyce Penner (University of Michigan). The study showed that uncertainties in biogenic VOC emissions are a significant contributor to the total uncertainty associated with estimates of global radiative forcing of aerosols. A biogenic VOC model was integrated into the NCAR Community Climate System Model [CCSM] Land Surface Model [LSM] and used to investigate the sensitivity of emissions to climate and land cover in collaboration with Sam Levis and Gordon Bonan (CGD). Biogenic VOC emissions were sensitive to climate, and the estimated interannual variability exceeded 10% of the estimated annual anthropogenic emission estimates used for the IPCC emission scenarios. Finally, a study examining interactions among global change (climate and land cover), biogenic isoprene emissions, and the chemical composition of the atmosphere was completed in collaboration with Tie, Ronald Neilson (U.S. Forest Service), and Claire Granier (CNRS). Climate and land cover-driven changes in biogenic VOC emissions impacted simulated regional surface ozone concentrations by as much as -30% to 50% under certain emission and climate scenarios. The ozone production chemistry was shown to change under different emission scenarios (i.e., NOx versus VOC) and has implications for unhealthy ozone concentrations and future ozone abatement strategies (see Figure 33).




Figure 33: Change in LN/Q for the month of July for [(FUTVEG-CURCLIM) – (CURVEG-CURCLIM)] (top) and [(FUTVEG-FUTCLIM) – (CURVEG-CURCLIM)] (bottom).

 

Model and Database Development (Tasks 1& 2)

Guenther and Wiedinmyer also developed a biogenic emission model and database for the scientific and air quality regulatory communities. FY04 accomplishments include the initial release (user’s guide and files are available on the NCAR community data portal, https://cdp.ucar.edu/) of the Model of Emissions of Gases and Aerosols from Nature (MEGAN) which predicts biogenic emissions on a global scale at 1 km resolution (Figure 34). MEGAN was also integrated with the NCAR global models, MOZART and the Community Land Model (CLM), and an effort was initiated to integrate MEGAN with regional air quality models.


 

 


Figure 34: Global annual isoprene emission distribution for the year 2000 estimated by the MEGAN model.

Instrument Development (Task 2)

Turnipseed, Guenther, Greenberg, and Karl developed instruments for investigating biosphere-atmosphere exchange in FY04. This included a Disjunct Eddy Accumulation (DEA) system that captures and stores air based on the vertical wind direction and speed. The concentrations in these stored samples (along with wind statistics) can then be used to determine fluxes of chemical trace species which are difficult to determine by other flux techniques which often need fast (< 1 s) measurement times. This project was in collaboration with Lamb and Mount, Shepson, and Steve Shertz (ATD). Two separate systems developed and evaluated in FY04 allow for DEA flux measurements of volatile organic compounds (VOCs) from both a tower and an aircraft platform.


Climate and Global Dynamics Division: CGD

The Biogeoscience initiative provided support for several projects in the Climate and Global Dynamics Division (CGD)'s Terrestrial Sciences Section (TSS) to implement biogeochemistry in the Community Land Model (CLM) and the Community Climate System Model (CCSM). This research broadly addresses how biogeochemical coupling of carbon, nitrogen, iron, and sulfur cycles affect climate, air quality, radiative forcing, and ecosystem function on regional to global scales. It involves two specific research agendas, related to mineral aerosols and the terrestrial carbon cycle. Highlights for the past year include the release of version 3 of the model (CLM3) and initial implementations of urban land cover and agricultural land in the CLM. This work mainly contributed to BGS Task 1, with the land-use-alteration studies also contributing to Task 4.

CGD-TSS members supported by BGS include Gordon Bonan, Samuel Levis, Keith Lindsay, Natalie Mahowald, Keith Oleson, Rosenbloom, and Peter Thornton. Bonan, Mahowald and Thornton are members of the BGS Steering Committee. Bonan co-chairs the CCSM Land Model Working Group, Mahowald co-chairs the CCSM Biogeochemistry Working Group, and other TSS scientists actively participate in both working groups, providing strong input to model development and implementing and testing model parameterizations.

Community Land Model (Tasks 1 & 4)

The Community Land Model (CLM) includes biogeophysics and hydrology, the traditional physical core components of land models, and is being further developed to include river routing, biogeochemistry (carbon, nitrogen, mineral aerosols, biogenic volatile organic compounds, water isotopes), and vegetation dynamics. Levis and Bonan analyzed the vegetation simulated by the dynamic global vegetation model in CCSM3. Their analyses showed that the prominent dry biases in the United States and the Amazon result in an inability to grow the expected forest vegetation. Changes to CLM3 that reduce the interception of water and increase transpiration result in a better simulation of vegetation (Figures 58 and 59).

Figure 58: Relative soil water wetness, canopy evaporation, and transpiration simulated by CLM3 (left) and a modified CLM3 (right). The modifications result in relatively wetter soil, reduced interception and canopy evaporation, and increased transpiration.

 


Figure 59: Vegetation simulated by CLM3 with its dynamic global vegetation model. Left: CLM3. Right: CLM3 with modifications that reduce interception and increase transpiration. The modifications allow for more extensive forests in eastern U.S. and tropical South America.

Land Cover and Land Use Change (Tasks 1 & 4)

A major research focus for CGD-TSS is natural and human-mediated changes in land cover and ecosystem functions and their effects on climate, water resources, and biogeochemistry. TSS scientists worked on several projects to implement land cover and land use change in CLM and to use climate models to study the impact of these processes on climate. This work contributes to the NCAR Weather and Climate Impact Assessment Science Initiative and the NCAR Biogeosciences Initiative.

Johannes Feddema (University of Kansas), Bonan, Oleson, and Linda Mearns (Environmental and Societal Impacts Group (ESIG)) studied the effects of historical and future land cover change on global climate. Climate model simulations were performed with the Parallel Climate Model (PCM) and examined the sensitivity of simulated climate to different specifications of present-day land cover and natural potential vegetation. Uncertainty in the classification of present-day vegetation can produce large differences in the simulated climate. Present-day vegetation has generally cooled surface climate, especially in the mid-latitudes due to the higher albedo of croplands compared to natural vegetation. Climate model simulations using land cover for the year 2100 showed that the land cover forcing of climate can be large, especially in tropical South America and in the United States, where agricultural land is projected to become more extensive by the year 2100.

Bonan, Oleson, and Feddema also worked to develop and implement an urban land cover parameterization for CLM. The parameterization uses concepts from urban canyon models to simulate the radiative balance of a city, turbulent energy fluxes, and the hydrologic cycle.

Agroecosystems differ from other terrestrial ecosystems due to their intensive management. Levis and Bonan worked to implement a crop model in CLM. The CLM is being modified from one crop type with prescribed leaf area index to include corn, wheat, and soybean, and to allow leaf area to grow in response to prevailing atmospheric conditions and management practices. The crop model is based on a model developed by Chris Kucharik, Jon Foley, and colleagues at the University of Wisconsin. This will provide a first order look at the sensitivity of climate to better specification of croplands.

Development of Carbon and Nitrogen Capabilities in CLM (Task 1)

 

The core biogeochemical capabilities for carbon and nitrogen cycling were implemented in CLM during FY 2003, as described in last years ASR. Over the past year these capabilities have been extensively evaluated and expanded, and long offline and coupled simulations have now been executed in a number of different configurations to demonstrate the readiness of the new model (CLM3-CN, Community Land Model – Carbon Nitrogen) for research applications. Thornton led or performed a range of development, evaluation, and model application activities over the past year, described in the following list:

  • Extensive testing of the new algorithm for seasonal and stress deciduous phenology.
  • Migration of the CLM2-CN code into the vectorized code base, to form CLM3-CN. Involved a complete reorganization of the implementation and referencing for nested hierarchical data structures. Demonstrated bit-for-bit correspondence with CLM2-CN.
  • Added new algorithm for prognostic canopy height as a function of stem mass and realistic allometric relationships.
  • Migration of sunlit/shaded canopy integration scheme from CLM2-CN into CLM3-CN. Included an improved treatment of canopy vertical gradient of specific leaf area for the purpose of calculating LAI from prognostic leaf carbon state variable.
  • Began discussions of implementation of water and carbon isotopes with David Noone (CU, water) and Ian Baker and Neil Suits (CSU, carbon).
  • Collaboration with J.F. Lamarque (ACD) to use nitrogen deposition fields from coupled CAM-chemistry model in offline mode in CLM3-CN and CCSM3 simulations.
  • Developed and implemented dynamic woody allocation algorithm.
  • Implemented gap phase mortality algorithm.
  • Extracted the sun/shade canopy integration code so that it could be incorporated in the CASA effort (Forrest Hoffman, ORNL).
  • Developed and implemented biological nitrogen fixation algorithm.
  • Began execution of long offline simulations examining the effects of preindustrial vs. current rates of nitrogen deposition, with J.F. Lamarque.
  • Began execution of experiments to document the influence of modified canopy integration scheme in the default model (non-CN) and in the CLM3-CN model. Included multiple 40-year experiments, both in offline and in coupled mode (CAM and CLM active).
  • Executed a series of experiments (with Mariana Vertenstein, CGD-TSS) to test the shift of CLM surface albedo call to the end of the CLM timestep. This is an important requirement for future implementation of isotopes. Verified that this modification does not changed coupled climate in CAM-CLM active mode.

 

Community Land Model Diagnostics Package (Task 1)

 

Since April 2004, Thornton has been leading an effort with Rosenbloom and Sylvia Murphy (CGD) to produce an updated diagnostics package for CLM. This activity was inspired by the need to modify the existing package to include new variables for the CN code, and our discovery that there were many “hard-wired” decisions in the existing package that made this sort of extension extremely tedious. They developed an architecture that allows for very flexible specification of new variables and new plotting types (or “sets”), while still maintaining all the functionality of the original package. They are in the process of implementing this architecture, and progress has been excellent. The combination of Thornton and Rosenbloom’s expertise on the scientific aspects and Murphy’s expertise on NCL has resulted in a very productive collaboration. Next steps include canvassing the land model and biogeochemistry Working Groups to identify new functionality that is required for current and future research efforts, and to implement this functionality.

 

First Results from CCSM3 with Coupled C and N Cycles (Task 1)

 

Offline simulations driven by the NCEP/NCAR reanalysis surface weather fields have demonstrated that the new land biogeochemistry behaves reasonably under prescribed atmospheric forcing. The first long simulations coupling the new land model to the atmosphere in CCSM3 (with prescribed ocean and ice boundary conditions) have just been completed, and the results suggest that both the improved canopy integration scheme and the prognostic carbon and nitrogen cycles have a significant impact on the coupled climate simulation. A major contributor to climate feedback in the new model is the prognostic canopy leaf area, which causes the seasonal, interannual, and long-term dynamics of the canopy to respond directly to the model climate, in contrast to the default land model which prescribes the seasonal cycle and spatial distribution of canopy leaf area from satellite observations (Figure 60). Next steps include simulations to quantify the climate feedbacks due to greenhouse forcing from prognostic carbon fluxes on land, and fully coupled simulations including the carbon cycle biogeochemistry of the oceans.

 

Multi-Century Carbon Cycle Simulations (Task 1)

 

Lindsay performed a suite of multi-century fully coupled carbon-climate integrations using a modified version of the Climate System Model, Version 1.4 (CSM1.4). A sequence of hundred year spin-up runs were done, with the aim of letting the modeled carbon cycle adjust incrementally to the coupled model climate. These spin-up runs led to a stable multi-century (1000 years) carbon-climate pre-industrial control run. Additionally, a multiple 180 year historical and 100 year future scenario fossil fuel emissions experiments have been completed. These experiments are being analyzed to understate connections and feedbacks between the carbon cycle and the physical climate.


 


Figure 60. Comparison of annual average leaf area index (LAI) for the default implementation of CLM3 in CCSM3 (top), and for the new implementation of CLM3-CN which includes prognostic carbon and nitrogen cycles (bottom). The CLM3 LAI is derived from remote sensing observations, and does not respond in any way to the modeled climate. The CLM3-CN LAI is a product of the prognostic development of vegetation canopy carbon and nitrogen state variables, with strong seasonal, interannual, and climatological responsiveness to the modeled surface weather and climate fields. The CLM3-CN result in this example is an intermediate result with nitrogen limitations turned off to achieve more rapid canopy development.


 

Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP) (Task 1)

 

Much of the work described above under the general category of CLM-CN development is relevant to the execution of the C4MIP experiments, but three efforts of special relevance to this project are listed here.

  • Thornton worked closely with Vertenstein and Brian Kauffman (CGD) to define new requirements for the data atmosphere component of CCSM3, which would allow actual CAM outputs to be read back in and fed to CLM in an offline mode through the coupler. This is an essential step in the involved process of bringing the CN model into steady state for preindustrial conditions. These requirements have been implemented and tested (Kauffman).
  • Thornton has defined the spinup protocol for the C4MIP experiments, working closely with Vertenstein and Hoffman to put together a project plan for the numbers and types of simulation segments that are required. Some technical aspects of the spinup are not yet deployed, but they have all been identified and progress is being made to allow the experiments to begin November 1, 2004.
  • Thornton has used the C4MIP protocol for prescribed transient landuse changes to define the requirements for the input datasets and the implementation of changing landcover within CLM (with Vertenstein). All of the raw datasets have been assembled and processed to produce both a preindustrial potential vegetation map and a timeseries of landcover from 1900-1990 that includes the fractional gridcell coverage for crops and pasture, and their changes through time. Thornton has also written the requirements for how the CN code needs to handle changes to and from all the possible combinations of landcover. Levis, Oleson, Vertenstein, and Thornton have also defined the requirements for handling water and energy conservation.

 

High-resolution Carbon Cycle Model User Interface Project (Task 1)

 

Thornton is PI on a project (started September 2003) sponsored by the NASA Earth Science Technology Office, to develop and implement a research-quality user interface for high-resolution carbon cycle simulation, using the Daymet and Biome-BGC models as technology components. The project involves a close collaboration with researchers in SCD to implement this interface as a web-based tool that can connect remote users to not only a set of state-of-the-art modeling tools, but also the high-end computational and data storage resources required to perform and analyze high-resolution simulations over large regions.

Accomplishments over the past year include:

·        Developed a formal System Architecture defining the interactions between software and hardware components, including the implementation of a Grid Service Interface connecting the User Interface with the Computational Engine.

·        Replaced the original client-side user interface application with a thin-client Web Portal User Interface

·        Introduced a project and data object model to manage the complex input and output requirements for the core science codes

·        Introduced a user authentication system to manage certification across distributed secure resources

·        Replaced the user-mediated interaction with the supercomputer resource from the original prototype with an automated job execution interface and job management service

·        Introduced Grid-based automated storage and retrieval mechanisms interfacing with the Mass Storage System.

 

Mineral Aerosols in CCSM (Tasks 1 & 4)

 

Mahowald's work has focused on three main issues: understanding the anthropogenic portion of desert dust, the climate and biogeochemical impacts of desert dust, and incorporating desert dust into the CCSM. In collaboration with university researchers (Jean-Louis Dufresne (UCSB/CNRS France), Chao Luo (University of California, Santa Barbara), Masaru Yoshioka (University of California, Santa Barbara), Mahowald contributed to two papers (one submitted, one published) on the relative proportion of anthropogenic mineral aerosol sources to the total sources, using Total Ozone Measuring Spectrometer Absorbing Aerosol Index (TOMS AII) and comparisons to observations. Additionally, she has one submitted article with a SOARS student (G. Rivera) and a university researcher (Chao Luo (University of California, Santa Barbara)) using desert dust storm data to constrain the land use fraction of current desert dust concentrations. Additionally she contributed to a paper looking at the importance of diurnal (surface energy flux processes) and synoptic processes in modulating the desert dust cycle (with Chao Luo (University of California, Santa Barbara) and Charles Jones (University of California, Santa Barbara).

Mahowald contributed to two papers dealing with the biogeochemical implications of mineral aerosols (with Greg Okin (Virginia), Ed Boyle (Massachusetts Institute of Technology) and many others). She authored an additional paper evaluating the atmospheric phosphorous sources over the Amazon (with university collaborators), which is in preparation. She worked with Jenny Hand (ASP) to develop the first modeling study of atmospheric iron in mineral aerosols as it is processed in the atmosphere and has a paper published on this topic, which is of great importance to the ocean biogeochemistry community. Mahowald's research also examined the impact of desert dust on African easterly waves as derived from observations with Charles Jones (University of California, Santa Barbara) and Chao Luo (University of California, Santa Barbara).

Mahowald has continued to improve the CCSM desert dust modeling codes and has looked at the response of atmospheric mineral aerosols and seasalts to climate change, using the CCSM in slab ocean model mode, for the current climate, preindustrial, doubled-CO2 and the last glacial maximum. This work is being done in collaboration with Phil Rasch (CGD-CMS), Charlie Zender (University of California, Irvine), Levis (CGD-TSS), Masaru Yoshioka (University of California, Santa Barbara) and Bette Otto-Bliesner (CCR).

 

Carbon in the Mountains Experiments: CME and ACME

The Biogeosciences Initiative sponsored the Airborne Carbon in the Mountains Experiment (ACME), an integrated program to quantify carbon fluxes in mountain and mountain-valley complex landscapes using airborne and ground-based flux measurement techniques. ACME is based in the Atmospheric Technology Division (ATD) with collaborations from scientists in CGD and MMM. External collaborators include University of Colorado (Russ Monson, Susan Buhr), Colorado State University (Dennis Ojima), University of Miami-Florida (Leolen Sternberg), University of Montana, and guest scientists from the University of Utah, Scripps Institution of Oceanography, and Washington State University. David Schimel (CGD) is principal investigator. ACME is coordinated with the Carbon in the Mountains Experiment (CME), a 5-year collaborative project between CU, CSU, U. Miami, and NCAR ATD, CGD, and MMM. CME is funded by the NSF Biocomplexity Initiative and also contributes to the NASA Interdisciplinary Science Program, and the interagency North American Carbon Program.

BGS supports the ACME contributions of Britton Stephens and Steven Shertz (both ATD), Jielun Sun and Sean Burns (both MMM), and Steven Aulenbach (CGD). The CME and ACME programs contribute to BGS Tasks 2 and 3.

The Airborne Carbon in the Mountains Experiment (ACME) combines measurements and innovative modeling techniques at regional scales. Techniques for quantifying carbon fluxes in complex landscapes are urgently required because much of the actively growing forest in Northern Hemisphere mid-latitudes occurs in such regions. Mountainous terrain also confers methodological advantages. Much of the uncertainty in carbon models is in the respiratory processes or the release of photosynthetically fixed carbon back to the atmosphere. This measurement is challenging in level landscapes, since eddy covariance fails in (common) stable nighttime conditions. In the mountains, concentration measurements in nighttime drainage flows allow “scaling up” of respiratory fluxes to airshed or “carbonshed” scales. This gives access to a key unknown quantity at a range of large scales.

ACME/CME studies were carried out in summer 2004. The airborne program (ACME I) involved 54 flight hours using the NCAR C-130 and explored a number of techniques for estimating carbon fluxes, in particular separating nighttime and daytime fluxes. The ground-based component, the Carbon in the Mountains Experiment (CME) deployed three Integrated Surface Flux Facility (ISSF) towers on Niwot Ridge, Colorado from July-October 2004, extending and complementing a permanent 2-tower flux array maintained by the US Geological Survey (USGS), and the University of Colorado. Each ACME flight included overpasses of the CME site, allowing extension of the results across scales. The combined experiment provides an innovative way of estimating landscape-scale parameters for land surface models, and a way of validating these models against regional airborne measurements. The separation of the airborne program into daytime (photosynthesis-respiration) and nighttime (respiration alone) fluxes allows the model to be tested much more rigorously than in previous studies where 24-hour measurements were made (Figures 61 and 62). This study is a pathfinder for upcoming intensives of the North American Carbon Program where this and other approaches for analyzing large-scale observations, model development, and model testing will be explored.

Figure 61: Morning and afternoon flight segments of a typical ACME day. Upper left: Early morning vertical profiling and low-level survey flights, along with the upwind segment of a semi-lagrangian flight (extension to the Northwest). Upper right: Afternoon flights showing the downwind segment of the semi-lagrangian experiment and low-level eddy covariance surveys.

 

Figure 62: Typical profiles from the ACME campaign. Lower left: Morning profiles indicating large accumulation of respired CO2 in the nocturnal boundary layer. These accumulations, also evident in low-level survey flights, suggest that large-scale drainage flows may be used to develop integrated estimates of respiration in the mountains. Lower right: Morning and afternoon profiles of CO2 from the semi-lagrangian experiment; CO profiles used to correct for pollution signals.

 

Carbon in the Mountains Experiment (CME) (Tasks 2 & 3)

Russ Monson (CU, principal Investigator), David Schimel (CGD), Britton Stephens (ATD), and Jielun Sun (MMM) are co-investigators in the CME project. Intensive observations at the Niwot Ridge Research Site in the first 6 months were conducted to investigate the local forest CO2 exchange. To enhance the existing carbon-cycle measurements (by CU and Dean Anderson, USGS) at this site, ATD staff (Steve Oncley, Steve Semmer, Kurt Knudson, Gordon Maclean) deployed 3 additional towers with instrumentation for measuring temperature, humidity, 3-dimensional winds, CO2 fluxes, and high-accuracy CO2 concentrations at multiple levels up to 30 m. The CO2 concentration instruments included the HYDRA system with 18 inlets developed and deployed by Tony Delany (ATD) Burns, and Sun (MMM), and three new AIRCOA units with six inlets each developed and deployed by Stephens and Andy Watt (ATD, see below). The tower measurements allow quantification of nighttime advective fluxes and can be inverted to estimate respiration. An animation in the MMM scientific report (Figure 40 animation) depicts CO2 evolution at the CME site.

The CME tower studies will be analyzed using a unique carbon process data assimilation model developed by University of New Hampshire and NCAR scientists including Schimel, which allows forest carbon fluxes from eddy covariance and advective techniques to be inverted into estimates of ecosystem model parameters. Preliminary studies have already demonstrated that key ecosystem parameters can be retrieved using this method. The model is being extended to include satellite vegetation estimates, water cycle measurements and isotopes. The process model currently being used (SPACENET) is a simplified version of the Common Land Model (CLM). As the information content of the flux data are better understood, we will begin assimilating parameters and states in the full CLM. Results from the SPACENET and CLM assimilations can be compared to fluxes estimated from the airborne program (ACME) using the CSU coupled atmospheric-land surface model (RAMDAS).

[ISFF field project web page: http://www.atd.ucar.edu/rtf/projects/cme04/]

[ISFF web page: http://www.atd.ucar.edu/rtf/facilities/isff/]


Airborne Carbon in the Mountains Experiment (ACME I) (Tasks 2 & 3)

 

ATD, MMM and CGD staff (Stephens, Sun, Schimel, Aulenbach, Bill Sacks and Teresa Campos) conducted the first Airborne Carbon in the Mountains Experiment (ACME I) in May and July 2004 to explore methods for constraining regional-scale CO2 fluxes over complex terrain and to collect measurements useful for devising and testing strategies for long-term monitoring of these fluxes. A total of 54 hours were flown on the NCAR C-130 aircraft over large regions of the Colorado Rocky Mountains, making continuous measurements of CO2, CO, O3, and water vapor concentrations (Campos, ATD), and collecting discrete flask samples for 13C and 18O isotope ratios in CO2 (University of Utah). In addition to these primary measurements, a number of other activities were conducted, including, measurements from the MCR scanning radiometer with thermal and vegetation channels (Mark Tschudi, ATD), collection of flask samples for radiocarbon measurements and for verification of our in situ CO2 and CO measurements (Scripps Institution of Oceanography), and collection of high rate CO2, CO, O3, and water vapor data for direct eddy-correlation flux estimates (Campos, ATD). Our airborne measurements will be compared to and integrated with the extensive ongoing carbon and ecosystem measurements at Niwot Ridge and an enhanced network of ground-based measurements deployed as part of the broader Carbon in the Mountains Experiment (CME).

The flights were conducted according to a combination of experimental designs, including morning to afternoon Lagrangian flux measurements, regional survey measurements for assimilation into a high-resolution ecosystem-atmosphere model, morning profile sampling of nocturnally respired CO2 and its concentration by topography and dispersion by turbulence, flask sampling to resolve elevation gradients in isotope signatures, and direct flux and eddy covarianve measurements. Preliminary data analysis results are encouraging. During the Lagrangian experiments and regional surveys, CO2 drawdowns of several ppm were observed in the daytime boundary layer, representing significant CO2 uptake by the forests and strong signals for use in the analyses. Also, in large mountain valleys we observed on the order of 30 ppm of respired CO2 pooling as deep as 1000 ft. overnight and persisting until 10 AM, which may suggest techniques for making respiration estimates on relatively large scales. Results are being analyzed using a mesoscale data assimilation system based on the RAMDAS coupled atmospheric-land surface model (CSU). Our results are already helping the community adapt plans for the North American Carbon Program to improve constraints on mountain carbon fluxes.

[collaborative web page with preliminary results and photos: http://swiki.ucar.edu/acme]


CO2 transport over complex terrain (Tasks 2 & 3)

In addition to their CME and ACME work, Sun and Burns (MMM) collaborated with Monson (University of Colorado) to collect meteorological, carbon dioxide, and flux data from the CU tower at Niwot Ridge as part of the ongoing Ameriflux program. The Ameriflux tower network, which covers North and South America, aims to improve the continental scale carbon budget.

The importance of downward transport of CO2 is becoming clear to the AmeriFlux scientific community, but the details of the mechanism and timing of such transport are still uncertain. Some researchers believe that observations from single towers may miss the advected CO2 at night, but can capture the missed CO2 during the day through observations of the CO2 turbulent transport. In addition, there is confusion on how to handle both horizontal and vertical advection of CO2. The combined dataset from the Niwot Ridge pilot experiment and 5 years of CU tower data are unique for examining all these issues.

Sun is systematically analyzing the data to examine all the CO2 transport mechanisms over the Niwot Ridge complex environment, including vertical and horizontal advection of CO2, horizontal turbulent transport of CO2, diurnal variation of CO2 storage, and detailed vertical turbulent transport of CO2 within and above the canopy layer. She has found that the advection of CO2 over mountain areas is clearly associated with local circulations, consisting of both horizontal and vertical advections even below 21m, and is sensitive to major steep slopes and small gullies embedded in these steep slopes. The local circulation reverses between night and day. The night-time CO2 transport over the slope explained the high CO2 observed at the North Park during ACME.  Sun also found that CO2 respiration from the ground cannot be effectively ventilated through the canopy, due to an unstable layer close to the ground resulting from shading by the canopy. CO2 advection could therefore play an important role even during daytime, when it was previously thought to be unimportant.

These observations provide critical information to the many on-going long term observational programs, which currently ignore horizontal transport in the global CO2 budget. They will be used to fully resolve the atmospheric transport of CO2 in order to accurately measure the net ecosystem carbon exchange, and as input to a regional-scale data-assimilation model to improve our understanding of the processes controlling carbon cycling by mountain forests.

Tower data collection and analysis will continue throughout FY05.  Sun plans to work to understand all the physical transport mechanisms over complex terrain and integrate the local CO2 balance.  She also hopes to implement these new physics into numerical modes to improve assimilations of CO2 transport over complex terrain.

Atmospheric Technology Division: ATD

The Atmospheric Technology Division, the Atmospheric Chemistry Division, and the Biogeosciences Initiative have been collaborating for several years to fund development and field support of airborne and tower-based in situ trace gas instruments. Supported developments include measurements of water vapor and ozone at fast-response in addition to carbon dioxide and carbon monoxide. The activities have been successful on several fronts in maintaining and improving the quality of community-requestable instrumentation and data sets.

 

Airborne CO2 Measurements (Task 2)

 

Teresa Campos (ATD) and co-workers modified the airborne CO2 instrument to enable high rate measurements of CO2 by the eddy covariance method. Preliminary results indicate successful deployment during the GOTEX campaign off the coast of Mexico (Ken Melville (Scripps Institute of Oceanography, and Carl Friehe (UC-Irvine)) and during ACME (Russell Monson, U Colorado, Schimel (CGD), Sun (MMM), and Stephens (ATD)). Spectral analysis of GOTEX marine boundary layer data imply an instrument frequency response of 4-Hz, and time series analysis implied a mixing ratio measurement precision of 0.2 - 0.3 ppmv (1-s for a 1-second average). The flux artifact of this sensor due to air motion sensitivity was quantified in both marine and terrestrial boundary layer environments during both missions by introduction of calibration gas into the sample cell during a portion of a boundary layer transect. Sensitivity to correlated air motion sensitivity was observed in GOTEX data only at frequencies lower than 2 Hz. However, the amplitude of these fluctuations is a factor of 50 smaller than the equivalent power spectral content of ambient data obtained in the marine boundary layer at the same altitude (Figures 6 and 7 from the above section on Chemistry Community Instruments). Preliminary ACME results from intercomparison to analyses of flask samples  (Heather Graham and Ralph Keeling, Scripps Institute of Oceanography) imply an accuracy of ± 0.2 ppmv. Also preliminarily, this result has been reproduced by intercomparison to CME ground network working standards provided and analyzed by the CO2 calibration facility (Stephens, ATD-RAF).

Figure 6:  Power spectral distribution of  two-minute ambient CO2 measurements of marine boundary layer air during the 2004 Gulf of Tehuantepec Experiment. Observations were made at 380 msl off the coast of Salina Cruz, Mexico.

  

Figure 7: The power spectral distribution of a two-minute time series during which CO2 calibration gas was sampled in-flight at 380 msl in the marine boundary layer. The measurement represents a quantification of the spectral dependence of the air motion sensitivity of the CO2 sensor.

 

Tower CO2 Measurements: Autonomous Inexpensive Robust CO2 Analyzer (AIRCOA) (Task 2)

 

In support of the CME deployment and future experiments to measure local and regional CO2 variations, Britton Stephens and Andrew Watt (both ATD) developed an autonomous, inexpensive, and robust CO2 analyzer [AIRCOA]. Four AIRCOA units were constructed after initial design testing and three of these were deployed in the field during the CME campaign. These units measure CO2 concentrations at 6 levels on a tower, producing individual measurements every 2.5 minutes precise to 0.1 ppm CO2 and closely tied to the WMO CO2 scale. A key component in the robustness of these analyzers is near real-time data processing with extensive automated diagnostic tests to verify normal operation, with new results available from a web interface every day.

[online diagnostics and results http://raf.atd.ucar.edu/~stephens/AIRCOA]

 

NCAR CO2 and O2 Calibration Facility (Task 2)

 

ATD staff (Stephens, Shertz, and Watt) have completed assembly of primary components of the NCAR CO2 and O2 Calibration Facility. These include a box to hold 25 large high-pressure gas cylinders oriented horizontally and insulated as necessary to prevent fractionation, a control module to selectively deliver pressure-regulated gases from these cylinders to a cryogenic drier and the concentration instrumentation, a high-precision commercial CO2 analyzer, a repackaged version of the RAF Oxygen Analyzer (ROXAN), and a suite of long-term (~20 years) calibration standards tied to Scripps Institution of Oceanography and NOAA CMDL WMO calibration scales. This facility was used to calibrate over 30 CO2 reference cylinders used in the CME and ACME campaigns.

[online diagnostics and results http://raf.atd.ucar.edu/~stephens/CALFAC]

 

Synthesis of Global Light Aircraft CO2 Data (Task 2)

 

In collaboration with CSU, NOAA CMDL, LSCE (France), U. Heidelberg (Germany), Max Planck Institute for Biogeochemistry (Germany), Tohoku U. (Japan), NIES (Japan), and CSIRO (Australia), Stephens completed a synthesis of vertical profile CO2 data from 20 sites around the world to define the vertical distribution of CO2 in the atmosphere. These results have been compared to output from the 16 TransCom 3 Project models to test their representation of vertical tracer transport. Stephens presented an invited seminar on this project at NOAA CMDL and a publication based on this work is in preparation.

 

Wisconsin Tall-Tower Atmospheric O2 Measurements (Task 2)

 

Stephens concluded three and half years of atmospheric O2 measurements at the WLEF tall‑tower research site, and returned equipment to the lab for reconditioning while future deployments are considered. Stephens presented an invited seminar on these measurements at the APO Conference in Jena, Germany and several publications based on this work are in preparation.


Publications 2003-2004

(Note:  Bold=university authors; *=institutional authors)

Refereed:

 

Austin, A. T., R.W. Howarth, J. S. Baron*, F. S. Chapin III, T. R. Christenson, E. A. Holland, M. V. Ivanov, A. Y. Lein*, L. A. Martinelli*, J. M. Melillo*, and C. Shang*, 2003:  Human disruption of element interactions: Drivers, consequences and trends for the 21st century, SCOPE volume on Multiple Element Interactions,  Island Press.

Bonan, G. B., S. Levis, M. Vertenstein, and K. W. Oleson, 2003: A dynamic global vegetation model for use with climate models: concepts and description of simulated vegetation dynamics. Global Change Biology, 9, 1543-1566.

Churkina*, G., J. Tenhunen, P.E. Thornton, E.M. Falge, J.A. Elbers, M. Erhard*, T. Grünwald, A.S. Kowalski, and U. Rannik, D. Sprinz*, 2003:  Analyzing the ecosystem carbon dynamics of four European coniferous forests using a biogeochemistry model, Ecosystems, 6, 168-184.

 

Dai, Y. J. , X. B. Zeng, R. E. Dickinson, I. Baker, G. B. Bonan, *M. G. Bosilovich, A. S. Denning, *P. A. Dirmeyer, *P. R. Houser, G. Y. Niu, K. W. Oleson, C. A. Schlosser, and Z. L. Yang, 2003: The Common Land Model. Bulletin of the American Meteorological Society, 84, 1013.

Dilling, L., S. C. Doney, J. Edmonds, K. R. Gurney, R. Harriss, D. Schimel, and B. Stephens, G. Stokes, 2003: The role of carbon cycle observations and knowledge in carbon management. Ann. Rev. Environ. Resources, 28, 521-558.

Fujita, D., M. Ishizawa*, S. Maksyutov*, P.E. Thornton, T. Saeki, and T. Nakazawa, 2003:  Inter-annual variability of the atmospheric carbon dioxide concentrations as simulated with global terrestrial biosphere models and an atmospheric transport model. Tellus, 55B(2), 530-546.

 

Gao, R.*, P. Popp*, D. Fahey*, T. Marcy*, R. Herman*, E. Weinstock, D. Baumgardner, T. Garrett, K. Rosenlof*, T. Thompson*, P. Bui*, B. Ridley, S.

Wofsy, O. Toon, M. Tolbert, B. Kärcher, Th. Peter, P. Hudson*, A. Weinheimer and A. Heymsfield, 2004: Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds, Science, 303, 516-520.

 

Gerbig, C., J.C. Lin, S.C. Wofsy, B.C. Daube, A.E. Andrews, B.B. Stephens, P.S. Bakwin*, and A. Grainger, 2003: Toward constraining regional-scale fluxes of CO_2 with atmospheric observations over a continent: 1. Observed spatial variability from airborne platforms, J.Geophys. Res., 108(D24), 4756, doi:10.1029/2002JD003018

 

Gerbig, C., J.C. Lin, S.C. Wofsy, B.C. Daube, A.E. Andrews, B.B. Stephens, P.S. Bakwin*, and A. Grainger, 2003: Toward constraining regional-scale fluxes of CO_2 with atmospheric observations over a continent: 2. Analysis of COBRA data using a receptor-oriented framework, J.Geophys. Res., 108 (D24), 4757, doi: 10.1029/2003JD003770.

Hand, J. L. , N. M. Mahowald, Y. Chen, R. L. Siefert, C. Luo, A. Subramaniam, and I. Fung, 2004: Estimates of atmospheric-processed soluble iron from observations and a global mineral aerosol model: Biogeochemical implications. J. Geophys. Res., doi:10.1029/2004JD004574, vol. 109, D17205.

*Hanson, P. J., *J. S. Amthor, *S. D. Wullschleger, *K. B. Wilson, R. F. Grant, A. Hartley, D. Hui, E. R. Hunt Jr., D. W. Johnson, J. S. Kimball , *A. W. King, *Y. Luo, *S. G. McNulty, G. Sun, P. E. Thornton, S. Wang, M. Williams, D. D. Baldocchi, R. M. Cushman , 2004: Oak forest carbon and water simulations: model intercomparisons and evaluations against independent data. Ecological Monographs, 74 (3): 443-489.

Harley, P., P. Vasconcellos, L. Vierling, C. Pinheiro*, J. Greenberg, A. Guenther, L. Klinger, S. De Almeida*, D. Neill*, T. Baker, O. Phillips and Y. Malhi, 2004: Variation in potential for isoprene emissions among Neotropical forest sites. Global Change Biology, 10, 630-650.

Hasenauer, H., K. Merganicova, R. Petritsch, S. Pietsch, and P. E. Thornton, 2003: Validating daily climate interpolations of complex terrain in Austria. Agricultural and Forest Meteorology119, 87-107.

Hauglustaine, D.*, L, F. Hourdin*, L. Jourdain*, M-.A. Filiberti*, S. Walters, J.-F. Lamarque, E. A. Holland, 2004:  Interactive chemistry in the Laboratoire de Meteorologie Dynamique general circulation model:description and background tropospheric chemistry evaluation , J. Geophys. Res., 109(D4), D04314, doi:10.1029/2003JD003957.

 

Holland, E. and M. Carroll, 2003: Atmospheric chemistry and the bioatmospheric carbon and nitrogen cycles. In Scope 61 Interactions of the Major Biogeochemical Cycles, pp. 273-292, eds., J. Melillo, C. Field and B. Moldan, Island Press, Washington, D.C.

Jones, C. , N. M. Mahowald, and C. Luo, 2004: Observational evidence of African desert dust intensification of easterly waves. Geophys. Res. Lett., doi:10.1029/2004GL020107, vol. 31, L17208.

Jones, C. , N. M. Mahowald, and C. Luo, 2003: The role of easterly waves on African desert dust transport. Journal of Climate, 16, 3617-3628.

Karl, T., A. Guenther, C. Spirig*, A. Hansel and R. Fall, 2003: Seasonal variation of biogenic VOC emissions above a mixed hardwood forest in northern Michigan. Geophys. Res. Lett., 30(23), 2186, doi:10.1029/2003GL018432.

 

Karl, T., A. Guenther, C. Spirig*, A. Hansel and R. Fall, 2004: Correction to “Seasonal variation of biogenic VOC emissions above a mixed hardwood forest in northern Michigan.” Geophys. Res. Lett., 31, L02110, doi:10.1029/2003GL019387.

 

Karl, T., M. Potosnak*, A. Guenther, D. Clark, J. Walker*, J. Herrick* and C. Geron*, 2004: Exchange processes of volatile organic compounds above a tropical rain forest: Implications for modeling tropospheric chemistry above dense vegetation. J. Geophys. Res., 109, D18306, doi:10.1029/2004JD004738.

 

Karl, T., T. Jobson*, W. Kuster*, E. Williams*, J. Stutz, R. Shetter, S. Hall, P. Goldan*, F. Fehsenfeld* and W. Lindinger, 2003: Use of proton-transfer-reaction mass spectrometry to characterize volatile organic compound sources at the La Porte super site during the Texas Air Quality Study 2000. J. Geophys. Res., 108(D16), 4508, doi:10.1029/2002JD003333

*Koster, R. D., *P. A. Dirmeyer, Z. C. Guo, G. Bonan, *E. Chan, *P. Cox, C. T. Gordon, *S. Kanae, *E. Kowalczyk, D. Lawrence, *P. Liu, *C. H. Lu, *S. Malyshev, *B. McAvaney, *K. Mitchell, *D. Mocko, *T. Oki, K. Oleson, A. Pitman, *Y. C. Sud, *C. M. Taylor, *D. Verseghy, *R. Vasic, Y. K. Xue, and *T. Yamada, 2004: Regions of strong coupling between soil moisture and precipitation. Science, 305, 1138-1140.

Law, B.E., O.J. Sun, J. Campbell, S. VanTuyl, and P.E. Thornton, 2003:  Changes in carbon storage and fluxes in a chronosequence of ponderosa pine, Global Change Biol., 9 (4), 510-524. 

Levis, S., G. B. Bonan, M. Vertenstein, and K. W. Oleson, 2004: The Community Land Model's Dynamic Global Vegetation Model (CLM-DGVM): Technical Description and User's Guide, NCAR TECHNICAL NOTE, NCAR/TN-459A, 50 pp.

Levis, S., C. Wiedinmyer, G. B. Bonan, and A. Guenther, 2003: Simulating biogenic volatile organic compound emissions in the Community Climate System Model. Journal of Geophysical Research – Atmospheres, 108, Art. No. 4659.

Lin, J.C., C. Gerbig, S.C. Wofsy, A.E. Andrews, B.C. Daube, C.A. Grainger, B.B. Stephens, P.S. Bakwin*, and D.Y. Hollinger*, 2004: Measuring fluxes of trace gases at regional scales by Lagrangian observations: Application to the CO2 Budget and Rectification Airborne (COBRA) study, J. Geophys.Res., 109, D15304, doi: 10.1029/2004JD004754.

Liu, X. J. , M. Walsh, X. T. Ju, F. S. Zhang, D. Schimel, and D. Ojima, 2004: NO and N2) fluxes from agricultural soils in Beijing area. Progress in Natural Science, 14, 489-494.

Luo, C. , N. M. Mahowald, and J. del Corral, 2003: Sensitivity study of meteorological parameters on mineral aerosol mobilization, transport, and distribution. Journal of Geophysical Research-Atmospheres, 108, Art. No. 4447.

Mahowald, N., C. Luo, 2003: A less dusty future? Geophys. Res. Lett., 30, 10.1029/2003GLO17880.

Mahowald, N., C. Luo, J. del Corral, and C. Zender, 2003:  Interannual variability in atmospheric mineral aerosols from a 22-year model simulation and observational data, J. Geophys. Res., 108 (D12), 10.1029/2002JD002821.

Mahowald, N., and J. L. Dufresne, 2004: Sensitivity of TOMS aerosol index to boundary layer height: Implications for detection of mineral aerosol sources. Geophys. Res. Lett., 31, 10.1029/2003GL018865.

Maria, S.F., L.M. Russell*, B.J. Turpin, R.J. Porcja, T.L. Campos, R.J. Weber, B.J. Huebert: Source signatures of carbon monoxide and organic functional groups in Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) submicron aerosol types, 2003, J. Geophys. Res. – Atmospheres, 108(D23), Art. No. 8637.

 

McKenzie*, D., D.W. Peterson*, D.L. Peterson*, and P.E. Thornton, 2003:  Climatic and biophysical controls on conifer species distributions in mountain forests of Washington State, USA. J. Biogeography, 30, 1093-1108.

Okin, G. S. , N. Mahowald, O. A. Chadwick, and P. Artaxo, 2004: Impact of desert dust on the biogeochemistry of phosphorus in terrestrial ecosystems. Global Biogeochemical Cycles, 18, Art. No. GB2005.

Oleson, K. W., G. B. Bonan, S. Levis, and M. Vertenstein, 2004: Effects of land use change on North American climate: impact of surface datasets and model biogeophysics. Climate Dynamics, 23, 117-132.

*Richard E. C., *K. C. Aikin, *E. A. Ray, *K. H. Rosenlof, *T. L. Thompson, A. Weinheimer, D. Montzka, D. Knapp, B. Ridley, and A. Gettelman, 2003: The distribution and variability of ozone in the summer sub-tropical upper troposphere and lower stratosphere: Large-scale equatorial transport during CRYSTAL-FACE. J. Geophys. Res., 108, 4714, doi:10.1029/2003JD003884.

Pressley, S., B. Lamb, H. Westberg, A. Guenther, J. Chen and E. Allwine, 2004: Monoterpene emissions from a Pacific Northwest Old-Growth Forest and impact on regional biogenic VOC emission estimates. Atmosph. Environ., 38, 3089-3098.

 

Schimel, D., 2004: Nutrient cycling and limitation: Hawai’i as a model system. Nature, 431, 630-631.

Schimel, D., 2004: The large-scale biosphere-atmosphere experiment in the Amazon. Ecological Applications, 14, S1-S2 Suppl. S.

Spirig, C., A. Guenther, J. Greenberg, P. Calanca* and V. Tarvainen*, 2004: Tethered balloon measurements of biogenic volatile organic compounds at a Boreal forest site. Atmos. Chem. Phys., 4, 215-229.

 

Stevens, Bjorn, D.H. Lenschow, I. Faloona, C.-H. Moeng, D.K. Lilly, B. Blomquist, G. Vali, A. Bandy, T. Campos, H. Gerber, S. Haimov, B. Morley, and D. Thornton: On Entrainment Rates in Nocturnal Marine Stratocumulus, 2003, Quart. J. Roy. Meteorol. Soc., 129(595): 3469-3493.

 

Townsend, A. R., R. W. Howarth, M. S. Booth*, C. C. Cleveland, S. K. Ollinger, A. P. Dobson, P. R. Epstein, E. A. Holland, D. R. Keeney, and M. A. Mallin, 2003:  Human health effects of a changing global nitrogen cycle, Frontiers in Ecology and the Environment, 1(5), 240-246.

 

Throop, H., E. Holland, W. Parton, D. Ojima and C. Keough, 2004: Effects of nitrogen deposition and insect herbivory on patterns of ecosystem-level carbon and nitrogen dynamics: results from the CENTURY model. Global Change Biology, 10, doi:10.1111/j.1365-2486.

 

Turnipseed, A., D. Anderson*, P. Blanken, W. Baugh and R. Monson, 2003: Airflows and turbulent flux measurements in mountainous terrain. Part 1. Canopy and local effects. Agricultural and Forest Meteorology, 119, 1-21.

 

Wang, G. L. , D. Schimel, 2003: Climate change, climate modes, and climate impacts. Annual Review of Environment and Resources, 28, 1-28.

Yi, C., R. Li, P. Bakwin*, A. Desai, D. Ricciuto, S. Burns, A. Turnipseed, S. Wofsy, J. Munger, K. Wilson* and R. Monson, 2004:  A nonparametric method for separating photosynthesis and respiration components in CO2 flux measurements. Geophys. Res. Lett., 31, L17107, doi:10.1029/2004GL020490.

Zhao, W., P. Hopke and T. Karl, 2004: Source identification of volatile organic compounds in Houston, Texas. Environ. Sci. Technol., 38, 1338-1347.

 

In review or in press:

Bond-Lamberty, B., S. T. Gower, D. Ahl , and P. E. Thornton, 2004: A reimplementation of the Biome-BGC model supporting multiple interacting vegetation types. Tree Physiology, in press.

Faloona, I., D. Lenschow, T. Campos, B. Stevens, M. van Zanten*, B. Blomquist*, D. Thornton* and Alan Bandy, Observations of entrainment in Eastern Pacific marine stratocumulus using three conserved scalars, J. Atmos. Sci., in press.

Holland, E. A., B. H. Braswell, J. Sulzman, and J.-F. Lamarque (in press, 2004), Nitrogen deposition onto the United States and western Europe: synthesis of observations and models, Ecol. Appl., in press.

House, J.* (CLA), M. Scholes, E. A. Holland, V. Brovkin, M. Assunçao Silva Dias, R. Betts, and U. Riebesell, 2004:  Atmospheric composition and climate regulation, in review, Millennium Ecosystem Assessment.

Knorr*, W., I.C. Prentice*, J.I. House* and E.A. Holland, 2004: Long-term sensitivity of soil carbon turnover to warming, Nature, in press.

Levis, S., and G. B. Bonan, 2004: Prognostic leaf area helps simulate observed springtime temperature patterns in the Community Atmosphere Model coupled to the Community Land Model. J. Climate, in press.

Pendall, E., S. Bridgham , *P. J. Hanson, B. Hungate, D. W. Kicklighter, D. W. Johnson, B. E. Law, Y. Luo, P. Megonigal, M. Olsrud, M. G. Ryan , P. E. Thornton, S. Wan , 2004: Belowground process responses to elevated CO2 and temperature: a discussion of observations, measurement methods, and models. New Phytologist, in press.

Pietsch, S. A., H. Hasenauer , and P. E. Thornton, 2004: BGC-model parameters for tree species growing in Central European forests. Forest Ecology and Management, in review.

Thornton, P. E., and N. Rosenbloom, 2004: Ecosystem model spin-up: estimating steady state conditions in a coupled terrestrial carbon and nitrogen cycle model. Ecological Modeling, in review.

Tie, X. X., A. Guenther, and E.A. Holland, 2004:  Biogenic methanol and its impacts on tropospheric oxidants, Geophys. Res. Lett., in press.

 

Non-Refereed:

Doney*, S.C., R. Anderson, J. Bishop*, K. Caldeira*, C. Carlson, M.-E. Carr, R. Feely, M. Hood, C. Hopkinson, R. Jahnke, D. Karl, J. Kleypas, C. Lee, R. Letelier, C. McClain, C. Sabine, J. Sarmiento, B. Stephens, and R. Weller, 2004: Ocean Carbon and Climate Change (OCCC): An Implementation Strategy for U.S. Ocean Carbon Cycle Science, UCAR, Boulder, CO, 108pp.

Faloona, I, D. Thornton, B. Blomquist, A. Bandy, D. Lenschow, T. Campos, S. Hall, Poster, AGU Fall Meeting, “Direct and indirect measurements of DMS, Ozone, and CO fluxes over the Eastern Pacific ocean”, December, 2003.

 

Guenther, A., 2003: Biogenic hydrocarbons (inc. isoprene). In Encyclopedia of Atmos. Sciences, 2385-2389.

 

E. A. Holland, J. Lee-Taylor, S. B. Bertman, M. A. Carroll, A. B. Guenther, P. B.Shepson, J. P. Sparks, 2004: A US Nitrogen Science Plan : Atmospheric-Terrestrial Exchange of Reactive Nitrogen, UCAR, Boulder, CO, 38pp.

 

Schimel, J. and E. Holland, 2004: Global gases. Chap. 19 in Principles and Applications of Soil Microbiology, pp. 491-509, eds., D. Sylvia, J. Fuhrmann, P. Hartel and D. Zuberer. Pearson, Prentice Hall, Upper Saddle River, NJ.

 

Sun, J., S. P. Burns, A. C. Delany, S. P. Oncley, A.Turnipseed, B. Stephens, A. Guenther, D. E. Anderson, and R. Monson, 2004: Carbon dioxide transport over complex terrain, 26th Agricultural and Forest Meteorology Conference, 23-26 August 2004, Vancouver, B C, Canada, Am. Met. Soc.

 

Wildfires Strategic Initiative

This work represents the activities of the ACD-BAI Group for the Wildfires Strategic Initiative.

Laboratory Studies

ACD-BAI scientists (Alex Guenther, Jim Greenberg, Peter Harley and Thomas Karl) are using laboratory facilities to characterize the processes that control biomass burning. Biomass burning studies were conducted in the NCAR-ACD laboratory roasting/burning chamber facility in collaboration with Hans Friedli (ASP) and in the United States Department of Agriculture (USDA) Missoula fire laboratory burn facility in collaboration with Robert Yokelson and Theodore Christian (both of University of Montana). The laboratory biomass burning studies demonstrated that oxygenated VOC and nitrogen compound emissions from fires are higher than most previous estimates and likely have an important role in fire dynamics (i.e., fuel ignitability) and regional air quality. This research also suggests that emissions of some compounds from smoldering fires (including charcoal production and post flaming phase pyrolysis) are underestimated in existing fire emission inventories.   Three manuscripts (Karl et al., Greenberg et al., Christian et al.) describing these results are in preparation for submission to peer-reviewed journals.

 

International Field Study

ACD-BAI scientists (Thomas Karl and Alex Guenther) participated in international investigations of biomass burning in FY04.  The FY04 CAPOS study in the Brazilian Amazon used airborne and ground measurements to characterize the primary emission composition of VOCs and other gases from tropical fires and within aging plumes in collaboration with Bob Yokelson, Theodore Christian (University of Montana), Don Blake (University of California, Irvine), Paulo Artaxo (University of Sao Paulo, Brazil), Joao Caravalho (CPTEC, INPE, Brazil).  The aircraft observations generally confirmed the emission profiles measured in the laboratory studies described above (Figure 32).


 

Figure 32: Altitude profile of monoterpenes above the Z34 tower close to Manaus

 

Modeling Studies

ACD-BAI scientists (Christine Wiedinmyer, Sreela Nandi and Alex Guenther) investjjigated impacts of fires on atmospheric chemistry using regional chemistry and transport models. FY04 studies included an investigation of the impact of future climate and landcover on regional air quality in the Pacific Northwest and NorthCentral U.S. in collaboration with Brian Lamb (Washington State University), Cliff Mass (University of Washington) and Susan Fergusen (U.S. Forest Service).  Another study focused on the influence of biomass burning on regional air quality in the Brazilian Amazon (with Hsiao-ming Hsu, MMM/RAP). This project included a detailed sensitivity study of emission inputs which demonstrated that there is a large difference in the fire emissions predicted using different methods recommended in the literature. The BAI Group also supported regional simulations of air quality in Mexico in preparation for the NCAR-ACD MIRAGE study with Xuexie Tie (ACD).

A modeling framework was developed to predict daily emissions from fires for all of North America at a 1km resolution for easy use in regional air quality model simulations. Fire emission inventories developed by this model will allow air quality modelers to include fire emissions with their model simulations and determine if fire emissions have a large impact on their air quality.

 

Upper Troposphere/Lower Stratosphere Strategic Initiative

 

The goal of the UTLS initiative is to plan and to conduct integrated studies of Upper troposphere and Lower Stratospheric dynamics, chemistry, microphysics and radiation using the new HIAPER aircraft in conjunction with observations from the NASA A-Train satellites and with NCAR modeling tools. During FY04, the UTLS initiative focused on four areas of activities.  These are field campaign planning, model development, instrument development, and satellite data analyses.

 

Following the NSF’s strategy of “Progressive Science”, a series of field campaigns is planned starting by transport studies using simple payload and existing instruments.  A Stratosphere-Troposphere Analyses of Regional Transport (START) experiment is planned and proposed for the HIAPER progressive science period (July to December 2005).  The START project aims to conduct an exploratory study of transport in the extra-tropical upper troposphere and lower stratosphere, while also testing the capabilities of HIAPER. Scientifically, the objectives of the START experiment are to (1) characterize the dynamic structure of the upper troposphere around the subtropical jet; (2) characterize the structure of the chemical transition layer from the troposphere to the stratosphere; and (3) examine the impact of deep convective outflow on the UTLS chemical composition, and ice and aerosol microphysics.  Testing and achieving confidence in the performance of the basic payload of instruments is also an important component of this experiment.  Laura Pan (NCAR/ACD) and Linnea Avallone (CU-Boulder) are co-principal investigators for this proposal.  Co- Investigators are Elliot Atlas (University of Miami), Ken Bowman (Texas A&M University), James Bresch (NCAR/MMM), Teresa Campos (NCAR/ACD/ATD), Andy Heymsfield (NCAR/MMM), Jennie Moody (University of Virginia), Don Lenschow (NCAR/MMM/ATD), Rushan Gao (NOAA/AL), Brian Ridley (NCAR/ACD), Steve Wofsy (Harvard University), and Mark Zahniser (Aerodyne Research, Inc.).

 

UTLS initiative coordinates and collaborates with the community effort of instrumentation development for HIAPER.  A main function for the initiative is to identify instrumentation needs for the key science issues.  One of the instruments under development, led by Alan Fried (ACD/ATD), is the new high performance airborne difference frequency generation instrument for the measurement of CH2O on HIAPER.  The trace gas formaldehyde (CH2O) is one of many important atmospheric trace species involved in ozone production and radical formation. The joint ATD/ACD Analytical Photonic and Optoelectronics Laboratory (APOL) has been actively involved in a long-term effort to carry out ever more accurate and precise measurements of this gas throughout the troposphere and lower stratosphere. An important component of this effort is the development of advanced autonomous instruments for operation on HIAPER.

 

Although we continue to make steady progress in the performance of our present airborne CH2O instrument, which employs a liquid-nitrogen cooled tunable diode laser (TDLAS), new technologies are critically needed to improve the performance even further, to significantly reduce system weight and size, and to eliminate the need for periodic operation intervention. To address this critical need, the APOL group has been developing an alternative system based upon difference frequency generation (DFG) to achieve these various goals.

 

Among the on going UTLS modeling effort, Mary Barth (ACD/MMM) in collaboration with William Skamarock and Si-Wan Kim implemented a simple gas and aqueous-phase chemistry mechanism into the WRF model to begin investigations on the effect of convection on the chemical environment.  Convection plays an important role in transporting pollutants from the surface to the upper troposphere, scavenging soluble species and depositing much of the soluble species to the surface, and converting species chemically in the cloud drops. Simulations of the 10 July 1996 STERAO storm were performed to provide a way to evaluate the modeled chemistry results with observations. Sensitivities of the chemical species distributions to the cloud microphysics representation are currently being investigated.  This WRF-AqChem model will continued to be developed by incorporating the aqueous chemistry modules into the community WRF-Chem model, by incorporating lightning production of NOx and interactions between gas and ice phase species. 

 

Satellite data analyses provide a global picture and context for more detailed balloon and in-situ aircraft observations.  Bill Randel (ACD) and Andrew Gettelman (ACD/CGD) are leading the activities using different sets of satellite data in the UT/LS. These data sets include both temperature and chemical species from a variety of platforms, including high resolution temperature measurements from GPS radio occultation, temperature, water vapor and cloud fields from the Atmospheric Infrared Sounder (AIRS) on the AQUA satellite. UT/LS satellite analyses are tightly coupled to efforts in other areas. Satellite observations are used to extend field campaign data, as well as employing data from aircraft to validate satellites, as indicated in Figure 63.  In addition, satellite analyses are linked to global modeling efforts, providing validation for global models.

 

Figure 63: Comparisons between in situ WB57 aircraft observations and AIRS satellite retrievals during the PreAVE mission off of Costa Rica in January 2004 showing excellent agreement for A) Temperature B) Water Vapor C) Ozone and D) Relative Humidity. Standard error and r2 values are indicated. Solid lines are 1:1 line, dotted lines are linear fits.

 

 

Megacity Impact on Regional and Global Environments (MIRAGE) Strategic Initiative

 

The MIRAGE Strategic Initiative supported coordination and modeling activities related to studies of air pollution in and around megacities.  Xuexi Tie, Sasha Madronich, and visiting graduate students Zhuming Ying (York University) and GuoHui Li (TAMU), are collaborating with Georg Grell of NOAA/FSL to implement in WRF-Chem chemical modules developed at ACD and to apply the model to the planning of a major international field campaign, MIRAGE-Mex, planned for early 2006 by ACD on behalf of the atmospheric sciences community. The WRF-Chem model was successfully ported over the central Mexico region, with emissions data for Mexico City and the surrounding region, and was used to perform simulations at various resolutions (4 km, 6 km, and 12 km).  Mexico City emissions were implemented through a collaboration with Aron Jazcilievich (UNAM).  Preliminary results show that the modeled temperatures and winds reproduce well the observed diurnal cycles, but with a cold bias indicating that the “heat island” of the city is not yet well represented by the model.  The diurnal cycles and magnitudes of surface concentrations of CO, NOx (NO +NO2), and O3 within Mexico City compare well with observations, and show that the model is able to capture high pollution events.  In anticipation of the MIRAGE-Mex field campaign, the interactions of urban outflow plume with the surrounding region were studied. For this study, Alex Guenther and Christine Wiedinmyer provided current estimates of regional biogenic (vegetative) emissions, and Jean Francois Lamarque provided biomass burning emissions. Preliminary results show that this interaction leads to more regional O3 production than would be expected from the three sources (urban, biogenic, and biomass burning) taken in isolation (Figure 15 from above section on WRF-Chem).  These preliminary results have been presented at conferences (Tie, X, and S. Madronich, Modeling of Mexico City Air Pollution and Outflow with WRF-Chem, 5th WRF/14th MM5 User’s Workshop, June 22-25, 2004, Boulder, CO; Tie, X, and S. Madronich, Effect of mobile, biomass burning, and biogenic emission on Mexico City’s Air Pollution and Outflow, 13th International Scientific Symposium of Transport and Air Pollution, Boulder, September 13-15, 2004, Boulder, CO.)

The MIRAGE Strategic Initiative also sponsored three international researchers (Ashesh Prosad Mitra from India, Ioana Ionel from Rumania, and Aron Jazcilievich from Mexico) and two students (Gretchen Stevens from Harvard University and Faustino Reyes from UNAM, Mexico), to attend and present results of their research at the 13th International Symposium on Transport and Air Pollution, held at NCAR on 13-15 Sept. 2004.


Figure 15: Ozone (O3) concentrations simulated with the WRF-Chem model, showing the interaction between the Mexico City pollution plume with regional biomass burning and biogenic emissions. Upper panel shows the O3 resulting from urban emission only. Middle panel includes effects adding biomass burning emissions, which contribute NOx in the NOx-limited regime (far-field, ca. 200-300 km).  Lower panel adds biogenic emissions, which contribute hydrocarbons in the hydrocarbons-limited regime (near-field, 50-150 km).

 

NCAR Home Page National Center for Atmospheric Research University Corporation for Atmospheric Research National Science Foundation Annual Scientific Report ACD Home Page Atmospheric Chemistry Division Advanced Study Program Atmospheric Technology Division Climate & Global Dynamics Environmental & Societal Impacts Group High Altitude Observatory Mesoscale & Microscale Meteorological Division Research Applications Program Scientific Computing Division