Analysis of long-range transboundary transport (LRTT) effect on Korean aerosol pollution during the KORUS-AQ campaign

We investigated the influence of long-range transboundary transport (LRTT) on the aerosol concentrations in the Korean peninsula using the ground- and satellite-based remote sensing with back-trajectory calculations during the Korea-United States Air Quality (KORUS-AQ) campaign. Specifically, aerosol optical depth (AOD) observations from a geostationary satellite can directly provide the progression and evolution of aerosol plume transport. During high pollution cases in western Korea, we found the AOD enhancement over the Yellow Sea and east-central China, at maximum > 200% over the pathway of LRTT compared to the mean condition. Particularly, high AOD in the Shandong peninsula appears coincidentally with the high AOD over South Korea in a day, revealing the strong influence of the east-central Chinese emission. Back-trajectory patterns remarkably capture the movement of high AOD bands detected by the geostationary satellite monitoring. LRTT cases through the inside of boundary layer at east-central China usually contribute to the high AOD in Korea, while air masses above the boundary layer in north China and Mongolia do not much relate to the Korean pollution, showing the importance for both the direction and height of the air-mass movement. Travel speed is another significant factor to describe the LRTT effect. Despite the large effect of LRTT to both urban and rural sites in Korea, sometimes urban sites are more affected by the domestic emission when the air-mass travels shorter than similar to 250 km per day, notifying that the effect of Korean domestic emission cannot be negligible as well. Our findings reveal that usage of geostationary satellite observations enables us to better evaluate the influence of LRTT on the local air pollution.