Variations in major aerosol components from long-term measurement of columnar aerosol optical properties at a SKYNET site downwind of Seoul, Korea

We investigated the variations in major aerosol components using optical properties from a SKYNET site downwind of metropolitan Seoul under prevailing westerlies. The study period was March 2007 through February 2017 during which numerous measures to reduce air pollutants were implemented in both Korea and China. Major aerosol components, including mineral dust (MD), secondary inorganic ions (SII), and carbonaceous materials were estimated from optical properties, such as fine mode volume fraction (FMVF), single scattering albedo (SSA), and the difference of absorption aerosol optical depth (dAAOD) between 400 and 870 nm. Monthly variations in aerosol characteristics estimated from the optical properties were mostly consistent with the previous studies based on in-situ measurement data. As many studies reported the reduction of particulate matter (PM) in Northeast Asia, AOD also decreased along with the reductions of MD and SII. Secondary formation during the long-range transport played an important role in elevating AOD. However, for the specific case of high FMVF, high SSA, or low dAAOD, potential source regions of aerosols tended to be distributed in the eastern Korean Peninsula and over the East Sea, as the effects of local emissions became larger than those of longrange transport. Although AOD variations successfully revealed the overall characteristics of PM on the whole, in some cases, the variations of optical properties were not clearly related to those of aerosol components.