合肥市PM10 输送轨迹分类研究

应用聚类分析的方法,对2001—2005年合肥市逐日72 h后向轨迹按季节分类,结合PM10日均浓度观测资料,分析了不同输送轨迹与该地区PM10浓度之间的关系。结果表明:不同方向后向轨迹所对应的PM10平均浓度有明显不同;最高PM10平均浓度对应的后向轨迹在春、秋和冬季都是来自西北方向,它们与季节平均的相对距平分别为44%,20%和31%;夏季为东北方向,与季节平均的相对距平为20%;其次为本地轨迹,各季的相对距平分别为5%,16%,18%和17%。根据分析得出合肥地区6组易于出现高浓度PM10的后向轨迹及对应的天气形势,并简要分析了其特征。气溶胶的远程输送主要发生在自由大气层,区域输送主要发生在边界层内。合肥地区大气污染事件超过50%与远程输送有关。移动快的气团不一定对应低浓度的PM10。

Transport Trajectory Classifying of PM10 in Hefei

Cluster analysis was used to categorize the daily 72 h back trajectories of Hefei in each season during 5-year periods from 2001 to 2005.The relationship between PM10concentration and transport pattern was studied using the results of cluster analysis,together with the daily measurements of PM10.The results show that the average PM10concentration within clusters from different directions were different evidently.The highest average PM10concentration corresponded to the northwesterly trajectories in the seasons except for summer.The relative differences between the cluster-mean PM10concentration of northwesterly clusters and the seasonal average were 44%,20% and 31% for spring,autumn and winter,respectively.The highest average PM10concentration in summer corresponded to northeasterly back trajectories,itsrelative differencefrom seasonal averageis 20%.The cluster-mean PM10concentration within the local back trajectories were also higher than the seasonal average in all seasons,and the relative differences from seasonal average were 5%,16%,18% and 7% for the four seasons from spring to winter.We obtained six clusters of various back trajectories,which were conducive to the accumulation of pollutants in Hefei.By comparison of the six clusters of trajectory,we concluded that the long range transport of PM10mainly occurred in the free troposphere,and the regional transport mainly occurred in the boundary layer.More than 50% of the atmospheric pollution events were related withlong range transport.The PM10concentration with the quickly moving air mass were not necessary lower than those with slowly moving air mass.