Regulation of Synoptic Circulation in Regional PM2.5 Transport for Heavy Air Pollution: Study of 5-year Observation Over Central China

Regional transport of air pollutants is modulated by large-scale synoptic circulation, which has been poorly understood for heavy air pollution in the downstream receptor region. In the present study of 5-year (2015-2019) observation, we targeted the Twain-Hu Basin (THB), a region of heavy PM2.5 pollution over central China, to investigate the regulation of synoptic circulation governing regional PM2.5 transport for heavy air pollution. It was found that regional transport of PM2.5 predominated 65.2% of the heavy pollution events (HPEs) over the THB based on the statistics of observational environment and meteorology. By employing the FLEXPART-WRF model, the regional transport of PM2.5 from upwind areas in central and eastern China (CEC) to receptor region in the THB was identified with three prominent pathways in the northerly, northeasterly, and easterly directions respectively. We then used T-mode principal component analysis in conjunction with the K-means cluster method to categorize synoptic circulations, and it was recognized that three regional PM2.5 transport pathways for the HPEs over central China were governed respectively by three patterns of synoptic circulation over CEC with (a) weak high air pressure to the north (13.3%), (b) strong high air pressure to the northeast (46.7%), and (c) weak high air pressure to the east (40.0%). This study reveals a significant modulation of large-scale synoptic circulation for regional transport of air pollutants in environmental change.