Chemical Reactivity of the Remote Troposphere over the Ocean Basins observed by NASA's Atmospheric Tomography Mission (ATom)

The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic Oceans for four seasons. The 4 ATom deployments provided a continuous data stream for initializing global chemistry models and calculating the 24-hour chemical tendencies. Tendencies derived from 6 chemistry models using the ATom-1 MDS tend to agree and show a highly heterogeneous troposphere where globally 10% of the parcels control as much as 40% of the budget of O3 and CH4. Surprisingly, modeled probability densities (100-km cells) match ATom statistics (2 km parcels), indicating that most of the observed heterogeneity can be resolved with current global chemistry models. On the other hand, the models' own chemical climatologies underestimate O3 production (P-O3) below 4 km in both Pacific and Atlantic basins for ATom-1 because they have lower NOX levels than observed. All four deployments (ATom 1-4) show consistently high P-O3 levels, > 2 ppb/day, throughout the lower troposphere (0-5 km). We examine sensitivity factors to determine which species seem to be driving these reactivities, particularly where large air masses of high reactivity (10° latitude by 2 km altitude or more) are resolved in successive profiling.