Deconstruction of tropospheric chemical reactivity using aircraft measurements: the Atmospheric Tomography Mission (ATom) data

The NASA Atmospheric Tomography Mission (ATom) completed four seasonal deployments (August 2016, February 2017, October 2017, May 2018), each with regular 0.2–12 km profiling by transecting the remote Pacific Ocean and Atlantic Ocean basins. Additional data were also acquired for the Southern Ocean, the Arctic basin, and two flights over Antarctica. ATom in situ measurements provide a near-complete chemical characterization of the ∼ 140 000 10 s (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 h integration of the 10 s parcels. These parcels accurately sample tropospheric heterogeneity and allow us to partially deconstruct the spatial scales and variability that define tropospheric chemistry from composition to reactions. This paper provides a first look at 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 the key species and reactivities presented here. These statistics provide climatological metrics for global chemistry models, e.g., the large-scale pattern of ozone and methane loss in the lower troposphere and the more sporadic hotspots of ozone production in the upper troposphere. The profiling curtains of reactivity also identify meteorologically variable and hence deployment-specific hotspots 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, and T, and thus these ATom measurements make a substantial contribution to the understanding of model differences and even identifying model errors in global tropospheric chemistry.The data sets are in standard, readable NetCDF format and they contain the metadata needed to use them. I have inserted the NetCDF display listing of the contents in the README file because it is useful for the user to be able to see what is in the datasets before downloading them. This should help them find the correct data.Funding provided by: National Aeronautics and Space AdministrationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000104Award Number: Earth Venture Suborbital - 2Funding provided by: National Aeronautics and Space AdministrationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000104Award Number: NNX15AG57AFunding provided by: National Aeronautics and Space AdministrationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000104Award Number: 80NSSC21K1454The Modeling Data Stream (MDS) is 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 during ATom deployments 1–4. The MDS is merged observations and gap-filled (see published paper) with 10 s (2 km) average data, see Wofsy et al. (2018, 2021) and Thompson et al. (2022). The Reactivity Data Stream (RDS) is derived from the MDS using the UCI chemistry model in a manner described in Prather et al. (2017; 2018). See related papers and dataset DOIs below. An earlier version of the MDS (MDS-0) was used to calculate RDS with six independent chemsitry models, and these results are shown in the published paper. The MDS-0 and RDS-0 versions and other previous versions are not archived here because there were too many errors in the MDS, and so the RDS results should not be used further. If a next-generation multi-model comparison of the calculated reactivities is organized, it is recommended that the MDS-3 data be used