Estimating the transboundary budget of sulfate aerosols in Northeast Asia with NASA MERRA aerosol reanalysis data

Using the Modern-Era Retrospective Analysis for Research and Applications Aerosol (MERRAero) reanalysis data, we conducted an estimation of the impact of transboundary-transported sulfate aerosols from China, specifically the Beijing-Tianjin-Hebei (BTH) region and Shandong province, on the sulfate concentrations in Korea between 2004 and 2020. Our analysis revealed that the ground-level sulfate concentration at six sites in Korea experienced a significant decrease of over 40%, from 7.16 mu g m- 3 to 3.7 mu g m- 3 after 2013. The MERRAero reanalysis data provided insights into a yearly reduction of 0.8 mu g m- 3 in sulfate concentration for the BTH and Shandong regions, while Korea showed an annual decrease of 0.2 mu g m- 3. Notably, the BTH and Shandong regions and Korea displayed the strongest correlation in sulfate concentrations with a one-day lag, particularly during the winter season. With the exception of summer, approximately 49.79 ton km-2 month-1 of sulfate was transported from the BTH and Shandong regions of China to Korea, resulting in a net increase of 9.8 ton km-2 month-1. The highest influx of sulfate occurred in spring at 70.06 ton km-2 month-1. Despite the clear declining trend in sulfate concentrations across the study region, the transboundary transport of sulfate from the BTH and Shandong regions of China to Korea did not exhibit a decreasing trend. This underscores the importance of thoroughly investigating the formation process of these aerosols through photochemical reactions during their long-distance transportation over northeast Asia, in addition to conducting a comprehensive examination of precursor emissions related to secondary aerosols.