Estimation of optical properties for HULIS aerosols at Anmyeon Island, Korea

In this study, the sensitivity of the optical properties of carbonaceous aerosols, especially humic-like substances (HULIS), are investigated based on a one-year measurement of ambient fine atmospheric particulate matter (PM_2.5) at a Global Atmospheric Watch (GAW) station in South Korea. The extinction, absorption coefficient, and radiative forcing (RF) are calculated from the analysis data of water soluble (WSOC) and insoluble (WISOC) organic aerosols, elemental carbon (EC), and HULIS. The sensitivity of the optical properties on the variations of refractive index, hygroscopicity, and light absorption properties of HULIS as well as the polydispersity of organic aerosols are studied. The results showed that the seasonal absorption coefficient of HULIS varied from 0.09 to 11.64 Mm^-1 and EC varied from 0.11 to 3.04 Mm^-1 if the geometric mean diameter varied from 0.1 to 1.0 μm and the geometric standard deviation varied from 1.1 to 2.0, with the imaginary refractive index (IRI) of HULIS varying from 0.006 to 0.3. Subsequently, this study shows that the RF of HULIS was larger than other constituents, which suggested that HULIS contributed significantly to radiative forcing.