Contrasting synoptic weather patterns between non-dust high particulate matter events and Asian dust events in Seoul, South Korea

The serious degradation of regional air quality is a critical social issue in East Asia despite continuous efforts to reduce the emission of pollutants and their precursors. To better understand high-pollution events in this region, the synoptic weather patterns associated with springtime non-dust high PMic, (High PM10) events and Asian Dust events in Seoul, South Korea, are examined for the 2001-2018 period. It is shown that the two high-pollution events accompany different atmospheric circulations. While High PM10 events are associated with weak surface cyclonic circulations over the Southeast China, Asian Dust events are characterized by strong cyclones over Northeast China. Composite weather maps show that mid-tropospheric circulation anomalies are exactly the opposite between the two events with anticyclonic anomalies over the Korean Peninsula for High PM10 events but cyclonic anomalies for Asian Dust events. The cluster analyses further reveal that High PM10 events are not determined by a single dominant weather pattern. They are associated with surface cyclonic circulations from southeastern China to the Sea of Okhotsk, anticyclonic circulations around the Korean Peninsula or their mixtures. This result is in contrast with the Asian Dust events which are primarily driven by vertically well-organized continental cyclones.