The impact of large-scale circulation on daily fine particulate matter (PM_(2.5)) over major populated regions of China in winter

Abstract

Using a new high-resolution air quality reanalysis dataset for China for five winters from December 2013 to February 2018, we examine the influence of large-scale circulation on daily PM_(2.5) variability through its direct effect on key regional meteorological variables over three major populated regions of China: Beijing-Tianjin-Hebei (BTH), the Yangtze River Delta (YRD) and the Pearl River Delta (PRD). In BTH, a shallow East Asian trough curbs northerly cold and dry air from the Siberian High, enhancing PM_(2.5) pollution levels. Weak southerly winds in eastern and southern China, associated with a weakened Siberian High, suppress horizontal dispersion, contributing to air pollution accumulation over YRD. In PRD, weak southerly winds and precipitation deficits over southern China are conducive to high PM_(2.5) pollution levels. To account for these dominant large-scale circulation- PM_(2.5) relationships, we propose three new circulation-based indices for predicting different levels of air pollution based on regional PM_(2.5) concentrations in each region: a 500 hPa geopotential height-based index for BTH, a sea level pressure-based index for YRD and an 850 hPa meridional wind-based index for PRD. These three indices can effectively distinguish clean days from heavily polluted days in these regions, assuming variation is solely due to meteorology. We also find that including the most important regional meteorological variable in each region improves the performance of the circulation-based indices in predicting daily PM_(2.5) concentrations on the regional scale. These results are beneficial to understanding and forecasting the occurrence of heavily polluted PM_(2.5) days in BTH, YRD and PRD from a large-scale perspective.