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PM2.5, a critical air pollutant, requires health-conscious management, with concentrations varying across regions due to diverse sources. This study, conducted in South Korea in 2021, employed the geographically weighted regression model to analyze the spatiotemporal correlations of PM2.5 with O3 and the normalized difference vegetation index (NDVI). Regional differences in the correlation between PM2.5 and O3 were observed, influenced by common precursors (SOx, NOx, and volatile organic compounds (VOCs)), seasonal temperature variations, and solar radiation differences. Notably, PM2.5 and O3 exhibited a heightened regression coefficient in summer, emphasizing the need for specific management targeting VOCs and NO2. The interplay between PM2.5 and NDVI revealed a negative overall impact but a positive effect in the central region of Korea, suggesting vegetation's role in the PM2.5 concentration increase due to atmospheric stagnation caused by mountain ranges. These findings enhance our understanding of PM2.5 distribution mechanisms, highlighting the need for tailored policies in each region for effective concentration reductions. [ABSTRACT FROM AUTHOR]

The impact of crop residue burning in northeastern China on South Korean PM2.5 concentrations was assessed via weather conditions, air quality modeling (AQM), and PM2.5 composition data during two cases exceeding 35 µg·m−3 in November 2015. PM2.5 concentration simulations of Case 1 differed from observations by 3.7–17.6 µg·m−3, overestimating the levels by 6–36%; however, Case 2 varied by 20.0–59.8 µg·m−3 from observations, with a 53–91% underestimation. Case 1 was generally well simulated, whereas the Case 2 simulation failed because the emissions of crop residue burning in northeastern China, as confirmed through satellite analysis (MODIS fires and thermal anomalies) and previous research, were not considered. The portion of organic/elemental carbon ratio during Case 2 was 1.6–2.3 times higher than that of Case 1. These results suggest that it is necessary to consider the effects of crop residue burning in northeast China to establish countermeasures to improve air quality and air quality forecasting in South Korea. [ABSTRACT FROM AUTHOR]

High particulate matter (PM2.5) concentrations have been considered a serious environmental issue in South Korea. Recent studies have focused mostly on metropolitan and industrial cities; however, high PM2.5 episodes have also been frequently observed even in small– and middle-sized cities. Thus, in this study, PM2.5 and its major chemical components were measured in a small residential city with low anthropogenic emissions for 2 years to identify the factors affecting the PM2.5 concentrations. Overall, the average PM2.5 concentration was 29.4 μg m−3: about two times higher than the annual ambient air quality standard value. In winter, when the PM2.5 concentrations were generally higher, relative humidity (RH) was significantly correlated with both PM2.5 mass and the PM2.5/PM10 ratio, suggesting that high RH promoted the formation of secondary PM2.5. In addition, SO42− and NO3− were found to be correlated with both NH4+ and K+ in winter, indicating that biomass burning was an important source in this city. Water-soluble organic carbon (WSOC) was also highly correlated with elemental carbon (EC) and K+ in fall and winter, when the burning of agricultural residues actively occurred. During high concentration episodes, NO3− exhibited the highest increase; nevertheless, other components (e.g., K+ and organic carbon) also significantly increased. [ABSTRACT FROM AUTHOR]