偏东风输送导致的泸州市冬季PM_(2.5)重污染过程分析

Analysis of a PM_(2.5) heavy pollution incident in Luzhou City caused by easterly wind transport in winter

为了探究四川盆地冬季大气重污染过程的成因,本研究以2022年12月18—25日川南地区典型城市泸州市的PM_(2.5)重污染事件为例,基于HYSPLIT模型并结合多源数据,使用天气分析、轨迹聚类、潜在源贡献分析法和浓度权重轨迹分析法,综合分析了此次过程的污染形成机制及传输特征.结果表明:①区域输送导致污染过程中出现多次ρ(PM_(2.5))(PM_(2.5)浓度)快速上升现象:21日晚间ρ(PM_(2.5))小时均值迅速攀升并在一天内达到重度污染水平,而后伴随两次轻微下降又迅速回升,最后于25日凌晨起迅速下降至35μg·m^(-3)以下.②稳定大气条件下的局地尺度气旋是输送通道形成的重要条件:在高压脊控制下泸州市保持晴朗、高温(日均气温约为8.5℃)、高湿(最高达100%)、小风(平均风速1 m·s^(-1))及较低边界层高度的静稳天气形势,且泸州和重庆交界处局地中尺度气旋导致的偏东风加强了污染物的区域输送,加之泸州南部山脉的地形阻滞,污染物难以扩散并在泸州北部辐合形成污染物滞留区.③污染轨迹主要来自偏东的短距离输送,潜在源区主要位于重庆西部与泸州北部的交界地带.研究显示,持续的静稳天气形势叠加偏东风输送是此次川南地区泸州市大气重污染形成的主要原因.

To investigate the origins of severe winter pollution in the Sichuan Basin,this study examines a PM_(2.5) pollution episode in Luzhou City,a representative urban area in southern Sichuan Province,occurring from December 18th to 25th,2022.Utilizing the HYSPLIT model alongside diverse datasets,we conducted a thorough analysis of the pollution's formation mechanisms and propagation patterns.Various analytical methods,including meteorological analysis,cluster analysis,potential source contribution function,and concentration-weighted trajectory analysis,were employed to dissect the pollution event's causative factors and characteristics.The results suggest that:①Regional transport is a significant driver of the observed surges in PM_(2.5) levels during the pollution event.Notably,on the night of December 21st,PM_(2.5) concentration escalated rapidly,reaching hazardous levels within 24 hours.This was followed by two minor reductions and a swift resurgence,before a sharp decline to concentrations below 35μg·m^(-3) in the early hourly of December 25th.②Localized cyclonic activity under stable atmospheric conditions played a crucial role in establishing pollutant transport pathways.Dominated by a high-pressure ridge,Luzhou experienced tranquil,characterized by clear skies,elevated temperatures(with an average daily temperature around 8.5℃),high humidity(peaking at 100%),and stagnant air(with an average wind speed of 1 m·s^(-1)),coupled with a reduced boundary layer height.Easterly winds,induced by a mesocyclone at the Luzhou-Chongqing border,intensified the regional movement of pollutants.Furthermore,the obstructive southern mountainous terrain impeded pollutant dispersion,leading to the accumulation of pollutants and the formation of a retention zone in Luzhou's northern region.③The pollution’s trajectory predominantly involved short-range eastward transport,with the primary potential source area situated at the confluence of western Chongqing and northern Luzhou.The analysis suggests that the persistent stable weather conditions,in conjunction with the eastward transport of air masses,are the primary contributors to the severe air pollution episodes in Luzhou City,within the southern Sichuan Province.