北京市朝阳区重空气污染天气类型分析

Analysis of weather type during period of heavy air pollution days in Chaoyang District,Beijing

利用2011—2015年北京市朝阳区气象观测资料和PM_(2.5)大气成分监测资料,对朝阳区重空气污染的天气类型进行了系统的分析。结果表明:2011—2015年北京市朝阳区重空气污染天气类型大致可分为均压场型、低压辐合型和高压型3种。均压场型重空气污染大气基本为静稳状态,地表风力小,污染物易在低层逐渐累积;同时,受北京市周边地形的影响,朝阳区受均压场控制,具有明显的山谷风风向转变的日变化。低压辐合场对应低压槽前的上升运动,使周边污染物向低压中心积聚,从而导致出现重污染天气。高压型重空气污染主要是由于朝阳区位于地面高压的后部或底部,受高压后部或底部的偏南或偏东气流的影响,污染物区域输送显著,从而导致污染物浓度上升。总体来看,均压场型、低压辐合型和高压型3种重空气污染天气类型交替出现时,朝阳区可出现持续性重空气污染。

Based on the meteorological observational data and PM2.5concentration monitoring data in Chaoyang District,Beijing from2011to2015,weather types during heavy air pollution were analyzed.The results show that three weather types can be generally identified under heavy pollution conditions,i.e.,uniform pressure field,low pressure with convergence,and high pressure.For uniform pressure field type when heavy air pollution occurs,atmospheric stratification is stable and surface wind speed is weak,which results in the accumulation of pollutants at a low level.Meanwhile,due to the local topography effect,the mountain valley wind circulation becomes significant over the Chaoyang District.The weather type of low pressure with convergence is characterized by ascending motion in the front of the trough,which leads to the accumulation of pollutants in the center of low pressure and the formation of heavy air pollution.Under high pressure type,Chaoyang District locates in the rear or bottom of surface high pressure and is influenced by the southerly or easterly flows,and then pollutant concentration increased due to strong regional pollutant transport.On the whole,when three weather types appear alternately,persistent and heavy pollution easily occurs in Chaoyang District.