The Atmospheric Tomography Experiment (ATom): Photochemistry Controlling Methane and Ozone in the Bulk Troposphere over the Remote Ocean Basins

The Atmospheric Tomography Experiment (ATom) provides unique measurements of atmospheric composition on four seasonal, meridional, profiling transects of the central Pacific and Atlantic Oceans. These observations provide most all of the key chemical constituents involved in the photochemical reactions controlling the greenhouse gases ozone and methane. Flight paths are preset to give a representative, objective sampling of air parcels in the troposphere (0.5 to 12 km) where most of the photochemical loss of ozone and methane occurs. This talk presents the statistical distributions and covariation of the key species from ATom and compares with six global chemistry models. The reactivity (e.g., methane loss, ozone production and loss) of each parcel is used in these model-measurement evaluations to place emphasis on the location and composition of air parcels that matter most. ATom analysis points to specific model failing in terms of the frequency of occurrence of these photochemically 'hot' air parcels in the remote troposphere and possibly identifies a common cause for the overestimation of methane loss in most all models as well as the distinct regions of ozone production (upper troposphere) and loss (lower troposphere).