常州地区一次持续性霾天气过程分析

Analysis on a persistent haze process in Changzhou

利用常规气象观测资料和NCEP再分析资料对2013年12月1—8日常州地区一次持续性严重霾天气过程进行了综合分析。结果表明:常州地区此次持续性霾天气过程中高纬地区高层环流较平直,低层为弱西南暖湿气流,冷空气势力较弱;2013年11月30日常州地区位于地面"L"型高压顶部,偏西风对常州上游地区污染物的输送和12月1日清晨出现的逆温层,导致扩散条件较差是此次霾过程爆发的主要原因;持续的地面均压场控制和频繁出现的逆温层为霾提供了维持机制,12月9日的强冷空气造成了此次霾过程消散。持续性霾天气过程期间,温度露点差减小,相对湿度增大,风力减小,多为偏西偏南风,且近地面多为弱的上升运动,为霾的维持提供了稳定的层结和充足的水汽。常州地区此次霾天气过程的主要污染物为颗粒物(PM2.5、PM10),部分SO_2、NO_2及O_3等污染物通过协同转化作用生成颗粒物,导致霾粒子浓度剧增是此次霾过程爆发的重要内因;后向轨迹模式的模拟结果也表明常州上游地区污染物的输送对此次霾过程亦有贡献。

Using the conventional meteorological observations and the NCEP reanalysis data,a persistent haze process from December 1 to 8,2013 in Changzhou was analyzed comprehensively in this study. The results show that zonal circulation at high levels in the middle-high latitudes is straight during the haze event,and meanwhile the low levels are mostly controlled by the warm and moist southwesterly airflows,with very weak cold-air activities.The reasons for the haze outbreak are mainly due to the transport of upstream contaminants by westerly airflows caused by an＂L＂-type high pressure locates at Changzhou on November 30,and the existence of a thermal inversion layer is in the early morning of December 1. The continuous uniform pressure field and the frequent thermal inversion layer are the maintaining mechanism of the haze. The strong cold air front leads to the dissipation of the haze on December 9. The haze process is accompanied by decreasing dew point depression, the increasing relative humidity, the southerly and westerly weak winds,and the ineffective upward motion near the surface,which provides a stable atmospheric layer structure and appropriate water vapor for the haze maintenance. The main pollutants during the haze event are particulate matters（ PM2. 5,and PM10）. The gaseous pollutants such as SO_2,NO_2,and O_3 generate particulate matters through the cooperative transformation effect,and lead to the dramatic increase in pollutant concentrations,which is an important internal cause for the haze formation. The backward trajectory analysis illustrates that the transport of pollutants from the upstream region of Jiangsu province also contributes to the haze event.