A Global-Scale In Situ Dataset of Aerosol Properties to Constrain Models: Results from the Atmospheric Tomography Mission (ATom)

From August 2016 to May 2018, an instrumented DC-8 aircraft operated by NASA performed global measurements of aerosol composition and size distribution. Nearly continuous vertical profiles were made between ~0.18 and ~12 km altitude as the aircraft flew over the central Pacific and Atlantic oceans from ~83° N to ~86° S latitude in each of four seasons. Dry size distributions and single particle and bulk composition measurements were used to calculate aerosol hygroscopicity and reconstruct ambient size distributions based on measured relative humidity. Coarse-mode size distribution measurements made with an underwing aerosol/cloud probe were added to these data to produce an ambient size distribution from 2.7 nm to 50 μm in diameter every one minute of flight.

From these hydrated size distributions we calculated ambient optical properties, including single scatter albedo, extinction and absorption coefficients, and asymmetry parameter. By vertically integrating optical properties during each profile, aerosol optical depth (AOD) and absorption AOD were determined. The contribution to AOD from sea-salt, dust, sulfate-organic mixtures, black carbon, and particulate water were determined for each profile location (roughly every 5 degrees of latitude). The concentrations of cloud condensation nuclei available at different supersaturations were also calculated. This unique dataset of ambient aerosol properties determined from in situ measurements provides powerful constraints for satellite remote sensing measurements and global chemistry-climate models. Examples from different locations and aerosol types will be shown.