Chemical Patterns Controlling Tropospheric Ozone and Methane: The ATom Dataset

In four round-the-world deployments, the NASA Atmospheric Tomography (ATom) mission has built an extensive photochemical climatology of the remote troposphere based on profiling transects over the Pacific and Atlantic Oceans. ATom achieved its goal of defining in depth the chemical composition of air parcels, ranging from instantaneous photolysis rates and radicals like OH, to more slowly varying reactive species like CO and NOx, to aerosols ranging from new particles to long-range dust transport, and including the emission-driven fluctuations of the long-lived greenhouse gases. A range of corollary data including chemical models and meteorological data are linked with the in situ measurements**. For each of four seasons, ATom measured over 30,000 10-second air parcels (~2.5 km horizontally by ~0.16 km vertically), with more than half of these over the remote, but at times polluted, ocean basins, including spring and fall sampling over Antarctica.

This paper presents a model comparison, whereby the global chemistry models use the measured chemistry of the ATom parcels to calculate the sustained 24-hour rates for production/loss of ozone (P-O3, L-O3) and methane (L-CH4). The models generally agree on these reactivities (Rs) and confirm the important role of heterogeneity: the top 10% of parcels determine about half of the total reactivity, show some but limited overlap across the 3 Rs, and occur in patches throughout most flights. The top-10 parcels occur in the upper end of some key species distributions with abundances 3 times greater than the mean. We are able to characterize the chemical mix that makes air parcels hot (e.g., high levels of CH₂O, H₂O₂, acetone) or indicates the history and processing of those parcels (e.g., high levels of HNO₃, HCN, aerosols). We then examine the modeled climatologies for August (ATom-1) to determine if the models' chemistry and transport can represent the occurrence of such parcels, thus providing a focused, critical tool for model validation.

** https://doi.org/10. 3334/ORNLDAAC/1581

** https://espoarchive.nasa.gov/archive/browse/atom/DC8/MDS.