Parameterization of Size of Organic and Secondary Inorganic Aerosol for Efficient Representation of Global Aerosol Optical Properties

Accurate representation of aerosol optical properties is essential for modeling and remote sensing of 21 atmospheric aerosols. Although aerosol optical properties are strongly dependent upon the aerosol size distribution, 22 use of detailed aerosol microphysics schemes in global atmospheric models is inhibited by associated computational 23 demands. Computationally efficient parameterizations for aerosol size are needed. In this study, airborne 24 measurements over the United States (DISCOVER-AQ) and South Korea (KORUS-AQ) are interpreted with a global 25 chemical transport model (GEOS-Chem) to investigate the variation in aerosol size when organic matter (OM) and 26 sulfate-nitrate-ammonium (SNA) are the dominant aerosol components. The airborne measurements exhibit a strong 27 correlation (r = 0.83) between dry aerosol size and the sum of OM and SNA mass concentration ( M !"#$% ). A global 28 microphysical simulation (GEOS-Chem-TOMAS) indicates that M !"#$% , and the ratio between the two components 29 ( &’ ()* ) are the major indicators for SNA and OM dry aerosol size. A parameterization of dry effective radius (R eff ) for 30 SNA and OM aerosol is proposed, which well represents the airborne measurements (R 2 = 0.74, slope = 1.00) and the 31 GEOS-Chem-TOMAS simulation (R 2 = 0.72, slope = 0.81). When applied in the GEOS-Chem high-performance 32 model, this parameterization improves the agreement between the simulated aerosol optical depth (AOD) and the 33