北京夏季典型PM_(2.5)与O_3相继重污染事件分析

Analysis of the successive typical PM_(2.5) and O_3 heavy pollution episodes in summer of Beijing

根据北京市环境保护监测中心发布的PM_(2.5)和O_3小时质量浓度及气象、卫星遥感数据,分析了2013年7月2日至10日北京典型PM_(2.5)及O_3重污染过程的质量浓度特征及在大气边界层过程各个阶段的质量浓度演变。结果表明,北京夏季O_3质量浓度先于PM_(2.5)达到峰值,而天气型演变是导致这一现象的主要原因。具体过程为:1)重污染初始阶段,高压天气型利于前体物积累,PM_(2.5)及O_3质量浓度升高;2)在反气旋中部,由于各种污染物质量浓度较低,对大气紫外波段辐射的吸收较弱,导致该阶段紫外辐射强,因而加快了O_3生成的光化学反应,O_3质量浓度最先达到峰值;3)在反气旋后部,随PM_(2.5)质量浓度增加,辐射变弱,因此O_3质量浓度增加速度下降,而受高压后部影响,区域内PM_(2.5)经东南风输送通道进入北京,导致北京PM_(2.5)质量浓度相继达到峰值;4)在重污染清除阶段,在北方反气旋前部的冷锋清除作用下,PM_(2.5)及O_3质量浓度同时降低至谷值。

The present paper is engaged in an analysis of the successive typical PM（2.5） and O3 heavy pollution episodes in summer of Beijing.In this paper,we have made an exploration of the characteristic features of the representative PM2.5 and O3 heavy air pollution accidents and the variation of their concentrations at each stage of the atmospheric environment process based on the study of PM（2.5） and O3concentration data published by Beijing Municipal Environmental Monitoring Center and the national meteorological observation data in combination with the remote-sensing data.The findings and the careful analysis indicate that O3 concentration reached the peak value prior to PM（2.5）,which should account for the main evolution of the synoptic pattern.At the same time,the chief facts of our analysis tend to demonstrate the following evolutionary tendency of the meteorological features in Beijing Area.（1） At the beginning stage of the air pollution,the concentration of PM（2.5） and O3 tends to rise due to the accumulation in the center of anticyclone.（2） In the middle of anticyclone stage,the absorption of UV radiation turns to be very weak because of the low concentrations of various pollutants.And,as a result,the rising radiation during the center of anticyclone,the UV radiation tends to increase eonsequently.Therefore,the concentration of O3 is likely to reach the peak value prior to PM（2.5） under the control of the central anticyclone.（3） At the rear stage,it would be possible for the concentration of PM（2.5） to rise for the effect of the wind from the south.And,then,the high concentration of PM（2.5） may reduce the radiation at the rear of the anticyclone,so that O3 concentration tends to rise slowly.On the other hand,PM（2.5） reaches its top concentration due to the transportation caused by the southeast wind,which is likely to take place in the later period of the air pollution accidents affected by the rear of anticyclone.（4） Finally,at the clearing stage of the air pollution,both the concentrations of PM（2.5） and O3tend to drop dramatically due to the clearing function of the cold front of the strong north anticyclone.The results have a certain reference value to the warning and controlling of heavy air pollution event.