Geostationary satellite measurements of aerosol optical depth (AOD) over East Asia from the Geostationary Ocean Color Imager (GOCI) and Advanced Himawari Imager (AHI) instruments can augment surface monitoring of fine particulate matter (PM_2.5) air quality, but this requires better understanding of the AOD–PM_2.5 relationship. Here we use the GEOS-Chem chemical transport model to analyze the critical variables determining the AOD–PM_2.5 relationship over East Asia by simulation of observations from satellite, aircraft, and ground-based datasets. This includes the detailed vertical aerosol profiling over South Korea from the KORUS-AQ aircraft campaign (May–June 2016) with concurrent ground-based PM_2.5 composition, PM₁₀, and AERONET AOD measurements. The KORUS-AQ data show that 550 nm AOD is mainly contributed by sulfate–nitrate–ammonium (SNA) and organic aerosols in the planetary boundary layer (PBL), despite large dust concentrations in the free troposphere, reflecting the optically effective size and high hygroscopicity of the PBL aerosols. We updated SNA and organic aerosol size distributions in GEOS-Chem to represent aerosol optical properties over East Asia by using in situ measurements of particle size distributions from KORUS-AQ. We find that SNA and organic aerosols over East Asia have larger size (number median radius of 0.11 µm with geometric standard deviation of 1.4) and 20 % larger mass extinction efficiency as compared to aerosols over North America (default setting in GEOS-Chem). Although GEOS-Chem is successful in reproducing the KORUS-AQ vertical profiles of aerosol mass, its ability to link AOD to PM_2.5 is limited by under-accounting of coarse PM and by a large overestimate of nighttime PM_2.5 nitrate. The GOCI–AHI AOD data over East Asia in different seasons show agreement with AERONET AODs and a spatial distribution consistent with surface PM_2.5 network data. The AOD observations over North China show a summer maximum and winter minimum, opposite in phase to surface PM_2.5. This is due to low PBL depths compounded by high residential coal emissions in winter and high relative humidity (RH) in summer. Seasonality of AOD and PM_2.5 over South Korea is much weaker, reflecting weaker variation in PBL depth and lack of residential coal emissions.

Full List of Authors

Shixian Zhai¹, Daniel J. Jacob¹, Jared F. Brewer¹, Ke Li¹, Jonathan M. Moch¹, Jhoon Kim^2,3, Seoyoung Lee², Hyunkwang Lim², Hyun Chul Lee³, Su Keun Kuk³, Rokjin J. Park⁴, Jaein I. Jeong⁴, Xuan Wang⁵, Pengfei Liu⁶, Gan Luo⁷, Fangqun Yu⁷, Jun Meng⁸, Randall V. Martin⁹, Katherine R. Travis¹⁰, Johnathan W. Hair¹⁰, Bruce E. Anderson¹⁰, Jack E. Dibb¹¹, Jose L. Jimenez¹², Pedro Campuzano-Jost¹², Benjamin A. Nault^12,a, Jung-Hun Woo¹³, Younha Kim¹⁴, Qiang Zhang¹⁵, and Hong Liao¹⁶

• ¹Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
• ²Department of Atmospheric Sciences, Yonsei University, Seoul, Republic of Korea
• ³Samsung Particulate Matter Research Institute, Samsung Advanced Institute of Technology, 130 Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do, Republic of Korea
• ⁴School of Earth and Environmental Sciences, Seoul National University, Seoul, Republic of Korea
• ⁵School of Energy and Environment, City University of Hong Kong, Hong Kong SAR, China
• ⁶School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
• ⁷Atmospheric Sciences Research Center, University at Albany, Albany, New York, USA
• ⁸Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
• ⁹Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, USA
• ¹⁰NASA Langley Research Center, Hampton, VA, USA
• ¹¹Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
• ¹²Department of Chemistry, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
• ¹³Department of Civil and Environmental Engineering, Konkuk University, Seoul, Republic of Korea
• ¹⁴International Institute for Applied Systems Analysis (IIASA), 2361 Laxenburg, Austria
• ¹⁵Department of Earth System Science, Tsinghua University, Beijing, China
• ¹⁶Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing, China
• ^anow at: Center for Aerosol and Cloud Chemistry, Aerodyne Research, Inc., Billerica, MA, USA