Aerosol size distributions during the Atmospheric Tomography (ATom) mission:...

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Brock, C., C. Williamson, A. Kupc, K. Froyd, F. Erdesz, N. Wagner, M. Richardson, J. Schwarz, R. Gao, J. Katich, P. Campuzano-Jost, B. Nault, J. C. Schroder, J. Jimenez-Palacios, B. Weinzierl, M. Dollner, T. P. Bui, and D. M. Murphy (2019), Aerosol size distributions during the Atmospheric Tomography (ATom) mission: methods, uncertainties, and data products, Atmos. Meas. Tech., doi:10.5194/amt-2019-44.

From 2016-2018 a DC-8 aircraft operated by the U.S. National Aeronautics and Space Administration (NASA) made four series of flights, profiling the atmosphere from 150 m to ~12 km above sea level from the Arctic to the Antarctic

15 over both the Pacific and Atlantic Oceans. This program, the Atmospheric Tomography (ATom) mission, sought to sample the troposphere in a representative manner, making measurements of atmospheric composition in each season. This paper describes the aerosol microphysical measurements and derived quantities obtained during this mission. Dry size distributions from 2.7 nm to 4.8 µm in diameter were measured in-situ at 1 Hz using a battery of instruments: 10 condensation particle counters with different nucleation diameters, two ultra-high sensitivity aerosol size spectrometers (UHSAS), one of which

20 measured particles surviving heating to 300° C, and a laser aerosol spectrometer (LAS). The dry aerosol measurements were complemented by size distribution measurements from 0.5-930 µm diameter at near-ambient conditions using a cloud, aerosol, and precipitation spectrometer (CAPS) mounted under the wing of the DC-8. Dry aerosol number, surface area, and volume, and optical scattering and asymmetry parameter at several wavelengths from the near-UV to the near-IR were calculated from the measured dry size distributions (2.7 nm to 4.8 µm). Dry aerosol mass was estimated by combining the size distribution

25 data with particle density estimated from independent measurements of aerosol composition with a high-resolution aerosol mass spectrometer and a single particle soot photometer. This paper briefly describes the instrumentation and fully documents the aircraft inlet and flow distribution system, the derivation of uncertainties, and the calculation of data products from combined size distributions. Comparisons between the instruments and direct measurements of some aerosol properties confirm that in-flight performance was consistent with calibrations and within stated uncertainties for the two deployments

30 analyzed. The unique ATom dataset contains accurate, precise, high-resolution in-situ measurements of dry aerosol size distributions, and integral parameters, and estimates and measurements of optical properties, for particles <4.8 µm in diameter that can be used to evaluate aerosol abundance and processes in global models.

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