Observation of Light-Absorbing Aerosol Properties in Asian Continental Outflow

Abstract:

Light-absorbing aerosols, such as black carbon (BC) and brown carbon (BrC), have a significant effect on the Earth’s energy budget by reducing solar radiation reaching at the earth’s surface. However, the reliable determination of BC and BrC properties is difficult mainly due to the uncertainties and the large variability in the mass absorption cross section (MAC), which is an important factor to calculate mass concentration from aerosol light absorption coefficient measurement. In this study, MAC of BC was determined to calculate BC mass concentration from co-located Continuous Soot Monitoring System (COSMOS) and Sunset EC-OC analyzer at Gosan, Korea. The optical properties and mass concentration of BC derived from COSMOS were compared with those from Continuous Light Absorption Photometer (CLAP) to estimate the contribution of volatile aerosols in light absorption. Aerosol optical properties such as absorption and scattering coefficient showed distinct seasonal variations. Aerosol absorption coefficient and BC mass concentration derived from COSMOS were approximately 40 % lower than those from CLAP. This difference can be attributable to the removal of volatile aerosols (i.e., BrC) coexisting with BC. BC and BrC mass concentrations simulated by GEOS-Chem model were also presented. On the other hand, BC mass concentration measured at four regional background sites, Gosan, Korea and Fukue, Fukui and Hedo in Japan, by an identical COSMOS from January 2012 to March 2014 were analyzed. BC mass concentration at Gosan (0.29±0.29 μg m^-3) was the highest among the other sites but there was no significant difference statistically.