The impact of large-scale circulation on daily fine particulate matter (PM<sub>2.5</sub>) over major populated regions of China in winter

Abstract. Using a new high-resolution air quality reanalysis dataset for China five winters from December 2013 to February 2018, we examine the influence of large-scale circulation on daily PM2.5 variability through its direct effect key regional meteorological variables over three major populated regions China: Beijing–Tianjin–Hebei (BTH), Yangtze River Delta (YRD) and Pearl (PRD). In BTH, shallow East Asian trough curbs northerly cold dry Siberian High, enhancing pollution levels. Weak southerly winds in eastern southern China, associated with weakened suppress horizontal dispersion, contributing accumulation YRD. PRD, weak precipitation deficits are conducive high To account these dominant circulation–PM2.5 relationships, propose circulation-based indices predicting different levels based concentrations each region: 500 hPa geopotential height-based index sea level pressure-based YRD an 850 meridional wind-based PRD. These can effectively distinguish clean days heavily polluted regions, assuming variation is solely due meteorology. We also find that including most important variable region improves performance scale. results beneficial understanding forecasting occurrence PRD perspective.