Quantitative analysis of winter PM2.5 reduction in South Korea, 2019/20 to 2021/22: Contributions of meteorology and emissions

To quantitatively analyze the factors contributing to the change in winter PM2.5 concentrations in South Korea over the past three years (2019/20 to 2021/22), we used updated anthropogenic emissions, a nested version of the GEOS-Chem model, and ground-based observational data. Our study identified meteorological variability and changes in anthropogenic emissions from China and South Korea as the main factors influencing changes in PM2.5 concentrations. The model results showed low normalized mean biases (NMBs) (13 % to 25 % for China, -5 % to -1 % for South Korea) compared with the seasonal mean ground observations in winter, indicating the model's reliability. Over the past three years (2019/20 to 2021/22), the observed winter PM2.5 concentration in South Korea has decreased by an average of 21.2 % (15.9 % to 24.2 %) compared to the reference year (2018/ 19). Among the three factors considered, meteorological changes contributed the most to the PM2.5 reduction, with an average of 12.9 % (6.8 % to 17.3 %), followed by a decrease in anthropogenic emissions from China of 5.1 % (2.7 % to 7.9 %) and South Korea of 1.7 % (1.3 % to 1.9 %). In addition, the high monthly variability of meteorological fields drove the monthly variability of surface PM2.5 in South Korea, ranging from 12.8 % to 20.6 %. These results highlight the complex interplay of various factors affecting winter PM2.5 concentrations in South Korea.