06 Jan 2022
06 Jan 2022
Status: this preprint is currently under review for the journal ACP.

Airborne observation during KORUS-AQ show aerosol optical depth are more spatially self-consistent than aerosol intensive properties

Samuel E. LeBlanc1,2, Michal Segal-Rozenhaimer1,2,3, Jens Redemann4, Connor J. Flynn4, Roy R. Johnson2, Stephen E. Dunagan2, Robert Dahlgren2, Jhoon Kim5,10, Myungje Choi5,6,7, Arlindo M. da Silva7, Patricia Castellanos7, Qian Tan1,2, Luke Ziemba8, Kenneth Lee Thornhill8,9, and Meloë S. Kacenelenbogen2 Samuel E. LeBlanc et al.
  • 1Bay Area Environmental Research Institute
  • 2NASA Ames Research Center
  • 3Department of Geophysics, Porter School of the Environment and Earth Sciences, Tel-Aviv University
  • 4University of Oklahoma, School of Meteorology
  • 5Yonsei University
  • 6University of Maryland Baltimore County
  • 7NASA Goddard Space Flight Center
  • 8NASA Langley Research Center
  • 9Science Systems and Application Inc.
  • 10Particulate Matter Research Institute, Samsung Advanced Institute of Technology (SAIT)

Abstract. Aerosol particles can be emitted, transported, removed, or transformed, leading to aerosol variability at scales impacting the climate (days to years and over hundreds of kilometers) or the air quality (hours to days and from meters to hundreds of kilometers). We present the temporal and spatial scales of changes in AOD (Aerosol Optical Depth), and aerosol size (using Angstrom Exponent; AE, and Fine-Mode-Fraction; FMF) over Korea during the 2016 KORUS-AQ (KORea-US Air Quality) atmospheric experiment. We use measurements and retrievals of aerosol optical properties from airborne instruments for remote sensing (4STAR; Spectrometers for Sky-Scanning Sun Tracking Atmospheric Research) and in situ (LARGE; NASA Langley Aerosol Research Group Experiment) on board the NASA DC-8, geostationary satellite (GOCI; Geostationary Ocean Color Imager; Yonsei aerosol retrieval (YAER) version 2) and reanalysis (MERRA-2; Modern-Era Retrospective Analysis for Research and Applications, version 2). Measurements from 4STAR when flying below 500 m, show an average AOD at 501 nm of 0.43 and an average AE of 1.15 with large standard deviation (0.32 and 0.26 for AOD and AE respectively) likely due to mixing of different aerosol types (fine and coarse mode). The majority of AODs due to fine mode aerosol is observed at altitudes lower than 2 km. Even though there are large variations, for 18 out of the 20 flight days, the column AOD measurements by 4STAR along the NASA DC-8 flight trajectories matches the south-Korean regional average derived from GOCI.

We also observed that, contrary to prevalent understanding, AE and FMF are more spatially variable than AOD during KORUS-AQ, even when accounting for potential sampling biases by using Monte Carlo resampling. Averaging between measurements and model for the entire KORUS-AQ period, a reduction in correlation by 15 % is 65.0 km for AOD and shorter at 22.7 km for AE. While there are observational and model differences, the predominant factor influencing spatial-temporal homogeneity is the meteorological period. High spatio-temporal variability occur during the dynamic period (25–31 May), and low spatio-temporal variability occur during blocking Rex pattern (01–07 June). The changes in spatial variability scales between AOD and FMF/AE, while inter-related, indicate that microphysical processes that impact mostly the dominant aerosol size, like aerosol particle formation, growth, and coagulation, vary at shorter scales than the aerosol concentration processes that mostly impact AOD, like aerosol emission, transport, and removal.

Samuel E. LeBlanc et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-1012', Andrew Sayer, 01 Feb 2022
  • RC2: 'Comment on acp-2021-1012', Anonymous Referee #2, 10 Mar 2022

Samuel E. LeBlanc et al.

Data sets

KorUS-AQ Airborne Mission Overview Gao Chen

Model code and software

4STAR processing codes for 2020 4STAR Team, LeBlanc, S., Flynn, C. J., Pistone, K., Segal-Rozenhaimer, M., Kacenelenbogen, M. and Broccardo

Samuel E. LeBlanc et al.


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Short summary
Airborne observations of atmospheric particles and pollution over Korea during a field campaign in May–June 2016 showed that the smallest atmospheric particles are present in the lowest 2 km of the atmosphere. The aerosol size is less repeatable over distances than their optical thickness. We show this with remote sensing (4STAR), in-situ (LARGE) observations, satellite measurements (GOCI), and modeled properties (MERRA-2), and it is contrary to current understanding.