The Hailuogou background station is located in a region sparsely populated and far away from industrial zones.Therefore,the level of particulate matter concentration here is similar to that in background regions of the USA.Usually,concentration of various pollutants changes slowly and periodically,but there are peaks of pollutant concentration during some stages,which are found through real-time automatic monitoring.Statistics about this situation showed that concentration in the background station during 43 days in 2015 rose rapidly due to long-distance transmission.The average concentration of PM2.5 during these days was 19.4 μg/m3,twice as the annual average of concentration (8.3 μg/m3).Through conjoint analysis on data monitored by the background station in 2015 and information in the annual weather analysis,the author tracked pollutants on the basis of models of the HSPLIT 4.8 track.There are paths of airflows through which pollutants are transported from the South Asian Subcontinent to China at the altitude of 200 meters and 3700 meters above the Hailuogou national atmosphere background region.The cluster analysis on the backward trajectory of 200 meters showed that 84％ air masses of atmospheric pollution during time periods when the concentration range of PM2.5 monitored by the Hailuogou background station was abnormal come from the direction of the South Asian Subcontinent.Also,there were simultaneous rises in the level of concentration of other items monitored in the regular six programs.%海螺沟背景站地处人烟稀少、远离工业带区域,颗粒物浓度水平与美国背景区域相当,通常情况下各项污染物浓度呈周期性缓慢变化,但通过实时自动监测发现,也有部分时段出现污染物浓度急剧升高的现象,对这种情况进行统计分析,2015年共有43 d因远距离传输导致背景站浓度急剧升高现象,其间PM2.5平均质量浓度为19.4 μg/m3,比其年均质量浓度(8.3μg/m3)高1倍多.通过对2015年背景站监测数据与年气象分析资料的联合分析,结合HSPLIT 4.8轨迹模式对污染物来源进行溯源,在海螺沟国家大气背景区域的200、3 700 m 2个高度都存在南亚次大陆向中国境内输送的气流路径.后向轨迹200 m高度聚类分析结果:海螺沟背景站PM2.5监测值超“正常”浓度范围时段有84％的大气污染气团主要来自南亚次大陆方向,同时,常规6项其他监测项目的浓度水平也存在协同上升效应.
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