Two leading patterns of winter PM2.5 variations in eastern China before the outbreak of cold surge and their causes

Abstract

It has been revealed that cold surge (CS) is a favorable weather condition to dissipate haze over Eastern China (EC). However, the variation of PM2.5 Concentrations in EC (PCEC) during different CSs is less discussed. This study investigates the spatial and temporal variations of winter PCEC during CS based on PM2.5 concentrations and NCEP/NCAR reanalysis datasets from 1980 to 2019. Two leading modes of PCEC variations during CSs were obtained through Empirical orthogonal function (EOF) analysis. The results show that PCEC increased before the CSs related to the EOF1 (Type1 CSs) occurred and decreased afterwards. While the PCEC has been showing a decreasing trend from 5 days before to 5 days after the CSs related to EOF2 (Type2 CSs), composite analysis shows that circulation anomalies with stable blocking highs over the Ural Mountains and the Sea of Okhotsk can increase the PCEC by strengthening the anticyclonic anomaly over EC before the Type1 CSs outbreak. While circulation anomalies with two wave-trains in mid and high latitudes can improve air quality from 5 days before to 5 days after the Type2 CSs outbreak by strengthening the cyclonic anomaly with northerly wind component over EC. The differences in circulation anomalies associated with two types of CSs mainly exist on the time scale of 10–30 days since the circulation anomalies of Type2 CSs are accompanied by the wave-train structure of “+ - + -+” propagating along the subtropical westerly jet stream. The wave-train is negatively correlated with PCEC, and with the strongest signal 2–4 days before the CSs outbreak, which can be used as a potential indicator to predict the ability of CSs to dissipate PCEC.