Optical and chemical properties of long-range transported aerosols using satellite and ground-based observations over seoul, South Korea

Aerosols that are transported long distances to the Korean Peninsula due to seasonal weather conditions can affect the local air quality of South Korea. In general, the long-range transported aerosols are widely distributed and variable with respect to time and space. In this aspect, geostationary satellites can be used as a powerful tool for providing temporal and spatial variation of aerosols by sequentially observing a target area. In this study, select events of high-concentration aerosols transported to Seoul, the capital of South Korea, were identified and analyzed using aerosol optical properties retrieved from geostationary ocean color imager (GOCI) for the cold season (October–March) from 2015 to 2018. In addition to the satellite data, ground-based observations of particulate matter (PM) and backward trajectory models were used. Based on the trajectories of air masses simulated with the backward trajectory models, events of the long-range transported high-concentration aerosols (hereafter referred to as “LRT events”) were selected and classified into three types: yellow dust, PM traversing over the Yellow Sea (PM-YS), and PM passing through North Korea (PM-NK). Optical and chemical properties of the three LRT events were analyzed, and significantly different features were found. Yellow dust showed a relatively high mean depolarization ratio at 1020 nm (0.26), a low Ångström exponent between 440 nm and 870 nm (0.27), fine mode fraction at 500 nm (0.26), single scattering albedo at 440 nm (0.93), and lidar ratio at 675 nm (37 sr) compared with those during the other PM events. Moreover, the proportions of Ca+ concentrations to the water-soluble ions in PM2.5 and concentrations of Ca and Fe among inorganic elements in PM2.5 significantly increased during the yellow dust event. On the contrary, the PM events (PM-YS and PM-NK) had relatively high mean Ångström exponent (1.28 and 1.38), fine mode fraction (0.94 and 0.81), single scattering albedo (0.96 and 0.94), lidar ratio (66 sr and 44 sr), and low depolarization ratios (0.035 and 0.066). The ratios of NO3− and SO42− to water-soluble ions in PM2.5 were significantly increased during the high PM events. By comparing the two PM events, the volume median radius of fine mode particles and fine mode fraction of PM-YS were found to be considerably higher compared with those of PM-NK. Such different characteristics found in this study for the three LRT events indicate that optical and chemical analyses of