Opposite trends of cold surges over South China Sea and Philippines Sea and their different impacts on PM2.5 in eastern China

The variations in cold surge (CS) path can cause significant impacts on air pollution in the area it passes through. This study investigates impacts of CSs over South China Sea (CSSCS) and Philippine Sea (CSPHS) on PM2.5 concentrations in eastern China (PCEC) and their underlying mechanisms from 1979 to 2021. It was revealed that the CSSCS is accompanied by the continental high-pressure over East Asia and shows an upward trend. CSPHS is mainly affected by both the continental high-pressure over East Asia and the East Asian Trough over the Sea of Japan, showing a significant downward trend. Such difference in circulation anomalies is related to the different paths of the two types of CSs. Both observation and simulations indicate that more (less) Ural blocking in winter would lead to the cold air originating from the regions over Lake Baikal (Caspian Sea) to invade southward (eastward) along the northern (northwestern) path, resulting in more frequent CSSCS (CSPHS) and increased (decreased) winter averaged PCEC due to the anticyclonic (cyclonic) anomalies over eastern China. Such variations in winter averaged PCEC masked the synoptic signals that PCEC would decrease (increase) during CSSCS (CSPHS) outbreaks. Therefore, the increased frequency of atmospheric blocking over Ural Mountains in recent years has still played a worsening role in the intensification of PCEC.