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.