Ambient aerosol properties in the remote atmosphere from global-scale in-situ measurements
- 1Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80305, United States
- 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, United States
- 3Aerosol Physics and Environmental Physics, Faculty of Physics, University of Vienna, 1090 Wien, Austria
- 4Department of Chemistry, University of Colorado, Boulder, Colorado 80309, United States
- 5School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
- 6Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824, United States
- 7Langley Research Center, National Aeronautics and Space Administration, Hampton, Virginia 23681, United States
- 8Ames Research Center, National Aeronautics and Space Administration, Moffett Field, California 94035, United States
- 9Bay Area Environment Research Institute, Moffett Field, California 94035, United States
- 10Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- 11School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
- anow at: Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, United States
Abstract. 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). A 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, asymmetry parameter, extinction, absorption, Ångström exponents, and aerosol optical depth (AOD) at several wavelengths, as well as 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); these calculated parameters were in agreement with the direct observations within expected uncertainties.
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 relative to continental sources of aerosols, with sea salt and aerosol water dominating the column extinction in most remote environments and dust and biomass burning (BB) particles contributing substantially to AOD, especially downwind of the African continent. Contributions of dust and BB aerosols to AOD were also significant in the free troposphere over the North Pacific.
Comparisons of lognormally fitted size distribution parameters to values in a database commonly used in global models show significant differences in the mean diameters and standard deviations for accumulation-mode particles and coarse-mode dust. In contrast, comparisons of lognormal parameters derived from the ATom data with previously published ship-borne measurements in the remote marine boundary layer show general agreement.
The dataset resulting from this work can be used to improve global-scale representation of climate-relevant aerosol properties in remote air masses through comparison with output from global models and with assumptions used in retrievals of aerosol properties from both ground-based and satellite remote sensing.
Charles A. Brock et al.
Charles A. Brock et al.
Charles A. Brock et al.
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