Synergistic effects of synoptic and quasi-biweekly timescale atmospheric circulation patterns on PM2.5 concentration in South Korea

In recent years, South Korea has continued to experience high PM_2.5 events despite government efforts, posing a significant threat to human life. This study examines the relationship between high winter PM_2.5 concentrations in South Korea and atmospheric circulation patterns on synoptic and quasi-biweekly timescales. During the winters of 2018–2022, periodicities of 4–8 and 8–26 days were observed in PM_2.5 concentrations, playing a crucial role in high PM_2.5 events. Composite analysis revealed that while atmospheric conditions during high PM_2.5 events shared similar characteristics, their intensity and spatial extent varied. An anticyclonic anomaly was observed in the upper levels over the Korean Peninsula, and the dipole pattern of the mean sea level pressure (MSLP) weakened the Siberian High, reducing northerly winds and weakening the East Asian winter monsoon. Under this atmospheric circulation, both low planetary boundary layer height (PBLH) and stable atmosphere contribute to high PM_2.5 concentrations along with weak ventilation. Anticyclonic anomalies associated with trough intensity originated from different sources: synoptic-scale anomalies from the North Atlantic (∼13 days prior) and quasi-biweekly anomalies from Siberia (∼8 days prior), propagating southeastward as precursor signals. PM_2.5 transport contributions differed by timescale: synoptic events were dominated by transport from eastern China, while quasi-biweekly events showed greater contributions from northern China. When overlapping, these timescales exhibited a synergistic effect, creating more favorable conditions for extreme high-concentration events.