2015年12月下旬嘉兴地区持续性雾-霾污染过程分析

Analysis on the persistent haze-fog event in Jiaxing area in late December 2015

利用FNL再分析资料、自动气象站和环境监测站的小时观测数据及基于WRF-CHEM化学模式的排放源敏感性对比试验和高分辨率输出结果对2015年12月21—25日影响嘉兴地区的一次持续性雾-霾污染过程进行分析,结果表明:污染期间对流层中高层维持较强的西南急流,南支锋区发展明显,北支槽位置偏高,冷空气势力较弱,大尺度环流形势有利于维持稳定的大气层结结构.PM_(2.5)浓度明显上升时,地面均为西北气流所控制,而浓度下降与地面东北风回流有关.此次雾-霾污染过程期间,本地污染平均贡献率为42%,江苏地区次之约占23%.大气层结稳定时本地污染物的贡献率可达60%左右.两次冷空气过程中外来污染物的输送通量和浓度平流的强度明显不同.近地面不同高度上PM_(2.5)浓度差变化与平流累积贡献量的变化表现出较好的一致性,高层垂直平流较低层明显.

One persistent haze-fog event during 21—25 Dec. 2015 was analyzed based on the FNL re-analysis data,hourly observations from auto weather stations and environment monitor stations,sensitive experiments of inventory and results from the WRF-CHEM model. Our results indicated that the strong southwest jet exited in mid-upper troposphere during the pollution period. Because southern frontal zone significantly developed and northern trough located at higher latitude,cold air was weak. The situation of atmospheric circulation tended to form stable atmosphere structure and hence PM2.5 mass concentration maintained high level. When PM2.5 concentration increased significantly,the weak northwesterly winds prevailing on surface resulted in external pollutants＇ input. In additional,northeasterly backflow on surface decreased pollutants＇ concentration. During the polluted event,pollutant sources in the local area and Jiangsu Province contributed 42% and 23%,respectively. Under the static and stable atmosphere condition,the contribution rate of local pollutants increased up to 60%. The intensities of pollutant transport flux and advection during two cold air processes were significantly different.Vertical changes of PM2.5 mass concentrations at different leverls were consistent with contribution changes of advection accumulation. Vertical advection in upper level was more significant than that in lower level.