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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 for
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 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
PM2.5 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 PM2.5 pollution levels. To account for these
dominant large-scale circulation–PM2.5 relationships, we propose
three new circulation-based indices for predicting different levels of air
pollution based on regional PM2.5 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 PM2.5 concentrations on the regional scale. These
results are beneficial to understanding and forecasting the occurrence of
heavily polluted PM2.5 days in BTH, YRD and PRD from a large-scale
perspective.
