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In this study, domestic and foreign contributions to a severe PM2.5 episode in South Korea, in which “emergency reduction measures against particulate matter” were issued, were analyzed. During the period between 27 February and 7 March in 2019 when high PM2.5 concentrations occurred, the PM2.5 concentration in the Seoul metropolitan area (SMA) in South Korea was approximately 87.3 μg/m3 on average, and a severe PM2.5 concentration level of approximately 113.4 μg/m3 was observed between 3 March and 5 March. The results of the analysis conducted using the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model and meteorological observation data showed that northwesterly wind or westerly winds were formed during the P1 and P3 periods when the PM2.5 concentration markedly increased. When the PM2.5 concentrations in East Asia were simulated using the Community Multiscale Air Quality (CMAQ), it was found that the high PM2.5 concentrations that occurred in the SMA of South Korea were mostly affected by PM2.5 transported over long distances and following atmospheric stagnation. When the domestic and foreign contributions were evaluated using the brute-force method (BFM), the foreign and domestic contribution concentrations were found to be 62.8 and 16.8 μg/m3, respectively, during the target period of this study. It was also found that the foreign contribution was 78.8%, while the domestic contribution was 21.2%.

In this study, four types of sensitivity experiments (EG, EE, NG, NE; E: ERA-Interim, N: NCEP/DOE2, G: Grell scheme, E: Emanuel scheme) were performed to evaluate the simulation skills of RegCM4 released in July 2010 over the CORDEX (COordinated Regional Downscaling EXperiment) East Asia domain based on the combinations of boundary conditions (BC: ERA-Interim, NCEP/DOE2) and the cumulus parameterization schemes (CPS: Grell, Emanuel) for the 1989. The surface air temperature and precipitation data observed by the Korea Meteorological Adminstration were used to validate the simulation results over South Korea. The RegCM4 well simulates the seasonal and spatial variations of temperature but it fails to capture the seasonal and spatial variations of precipitation without consideration of the BC and CPS. Especially the simulated summer precipitation amount is significantly less in EG, NG, and NE experiments. But the seasonal variation of precipitation including summer precipitation is relatively well simulated in the EE experiment. The EE experiment shows a better skill in the seasonal march of East Asia summer monsoon, distribution of precipitation intensity and frequency than other experiments. In general, the skills of RegCM4 for temperature and precipitation are better during winter than summer, and in Emanuel than Grell schemes. The simulation results are more impacted by cumulus parameterization schemes than boundary conditions.

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