Roles of meteorological factors in inter-regional variations of fine and coarse PM concentrations over the Republic of Korea

This study examined meteorological effects on airborne concentrations of particulate matter (PM) of <2.5 μm (PM_2.5) and 2.5–10 μm (PM_2.5–10) diameter in 16 regions of Korea, including seven metropolitan cities and nine provinces. Regional distributions of mean PM concentrations indicate that PM_2.5 concentrations were higher in provinces than in metropolitan cities, while PM_2.5–10 concentrations were higher in the western than eastern regions, in the season with the highest concentrations during 2015–2019. Concentrations of PM of diameter <10 μm (PM₁₀), the sum of fine and coarse PMs, decreased over all regions during 2001–2019, particularly in Seoul, the capital of Korea. Mechanisms by which meteorological factors such as air temperature, wind, humidity, and air pressure control PM concentrations in Korea vary with region, season, and PM size. Regardless of emissions, >25% of PM_2.5 variability can be explained by Random Forest regression with only atmospheric variables, compared to little accountability for PM_2.5–10. The two most important variables that affect PM_2.5 variability are surface air temperature and wind. Transboundary transport controlled by atmospheric factors causes fine PM from northeast and east China to affect PM_2.5 variations a day after emissions in the northern-central and southern regions of Korea, respectively; and coarse PM from east China affects PM_2.5–10 variations in Korea on the same day. The present results suggest that local governments of regions with high PM concentrations should strengthen regulation policies with a long-term perspective, considering future changes in atmospheric conditions that may cause increases in PM levels.