Ambient aerosol properties in the remote atmosphere from global-scale in situ measurements

• Published in: Atmospheric Chemistry and Physics
• Main Authors: C. A. Brock, K. D. Froyd, M. Dollner, C. J. Williamson, G. Schill, D. M. Murphy, N. J. Wagner, A. Kupc, J. L. Jimenez, P. Campuzano-Jost, B. A. Nault, J. C. Schroder, D. A. Day, D. J. Price, B. Weinzierl, J. P. Schwarz, J. M. Katich, S. Wang, L. Zeng, R. Weber, J. Dibb, E. Scheuer, G. S. Diskin, J. P. DiGangi, T. Bui, J. M. Dean-Day, C. R. Thompson, J. Peischl, T. B. Ryerson, I. Bourgeois, B. C. Daube, R. Commane, S. C. Wofsy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Pacific; Aerosol Robotic Network; albedo; Atlantic Arctic; Atlantic-Arctic
• Online Access: https://doi.org/10.5194/acp-21-15023-2021; https://doaj.org/article/b30fdb8716f74ea1840853dee12c509c

In situ measurements of aerosol microphysical, chemical, and optical properties were made during global-scale flights from 2016–2018 as part of the Atmospheric Tomography Mission (ATom). The NASA DC-8 aircraft flew from ∼ 84 ∘ N to ∼ 86 ∘ S latitude over the Pacific, Atlantic, Arctic, and Southern oceans while profiling nearly continuously between altitudes of ∼ 160 m and ∼ 12 km. These global circuits were made once each season. Particle size distributions measured in the aircraft cabin at dry conditions and with an underwing probe at ambient conditions were combined with bulk and single-particle composition observations and measurements of water vapor, pressure, and temperature to estimate aerosol hygroscopicity and hygroscopic growth factors and calculate size distributions at ambient relative humidity. These reconstructed, composition-resolved ambient size distributions were used to estimate intensive and extensive aerosol properties, including single-scatter albedo, the asymmetry parameter, extinction, absorption, Ångström exponents, and aerosol optical depth (AOD) at several wavelengths, as well as cloud condensation nuclei (CCN) concentrations at fixed supersaturations and lognormal fits to four modes. Dry extinction and absorption were compared with direct in situ measurements, and AOD derived from the extinction profiles was compared with remotely sensed AOD measurements from the ground-based Aerosol Robotic Network (AERONET); this comparison showed no substantial bias. The purpose of this work is to describe the methodology by which ambient aerosol properties are estimated from the in situ measurements, provide statistical descriptions of the aerosol characteristics of different remote air mass types, examine the contributions to AOD from different aerosol types in different air masses, and provide an entry point to the ATom aerosol database. The contributions of different aerosol types (dust, sea salt, biomass burning, etc.) to AOD generally align with expectations based on location of the profiles ...