Deconstruction of tropospheric chemical reactivity using aircraft measurements: the ATom data

Abstract. The NASA Atmospheric Tomography (ATom) Mission completed four seasonal deployments (August 2016, February 2017, October 2017, May 2018), each with regular 0.2–12 km profiling through transecting the remote Pacific and Atlantic Ocean basins. Additional data are acquired also for the Southern Ocean and Artic basin, as well as two flights over Antarctica. ATom in situ measurements provide a near-complete chemical characterization of the ~140,000 10-second (80 m by 2 km) air parcels measured along the flight path. This paper presents the Modeling Data Stream (MDS), a continuous gap-filled record of the 10-s parcels containing the chemical species needed to initialize a gas-phase chemistry model for the budgets of tropospheric ozone and methane. Global 3D models have been used to calculate the Reactivity Data Stream (RDS), which is comprised of the chemical reactivities (production and loss) for methane, ozone, and carbon monoxide, through 24-hour integration of the 10-s parcels. These parcels accurately sample tropospheric heterogeneity and allow us to partially deconstruct the spatial scales and variability that defines tropospheric chemistry from composition to reactions. This paper provides a first look and analysis of the up-to-date MDS and RDS data including all four deployments (Prather et al., 2023, https://doi.org/10.7280/D1B12H).

ATom's regular profiling of the ocean basins allows for weighted averages to build probability densities for key species and reactivities presented here. These statistics provide climatological metrics for global chemistry models, for example, the large-scale pattern of ozone and methane loss in the lower troposphere, and the more sporadic hot spots of ozone production in the upper troposphere. The profiling curtains of reactivity also identify meteorologically variable and hence deployment-specific hot spots of photochemical activity. Added calculations of the sensitivities of the production and loss terms relative to each species emphasize the few dominant species that control the ozone and methane budgets, and whose statistical patterns should be key model-measurement metrics. From the sensitivities, we also derive linearized lifetimes of ozone and methane on a parcel-by-parcel basis and average over the basins, providing an observational basis for these previously model-only diagnostics. We had found that most model differences in the ozone and methane budgets are caused by the models calculating different climatologies for the key species such as O₃, CO, H₂O, NOx, CH₄ plus T, and thus these ATom measurements provide a substantial contribution to the understanding of model differences and even identifying model errors in global tropospheric chemistry.