北京一次近地面O3与PM2.5复合污染过程分析

利用O_3、PM_(2.5)监测数据、紫外辐射观测数据及气象观测资料,结合WRF模式模拟的大气环境背景场,分析了2014年9月3—8日北京一次近地层O_3与PM_(2.5)复合污染过程。结果表明,O_3和PM_(2.5)出现高质量浓度污染与大陆高压和副热带高压系统的相继持续控制有关,较强的紫外辐射及高压形成的下沉气流是造成边界层复合污染,尤其是O_3污染的主要原因。此次复合污染过程中,O_3于9月4—7日连续4 d超标,PM_(2.5)于9月5—7日连续3 d超标。造成这一现象的原因为:受大陆高压和副高的持续高压影响,北京地区天气晴朗、紫外辐射较强,地面风场较弱,700 h Pa以下持续存在下沉气流,O_3日均质量浓度逐日上升,于9月5日先到达峰值,同时PM_(2.5)日均质量浓度逐日升高;6日在副高西部边缘偏南暖湿气流输送及形成的平流逆温作用下,PM_(2.5)质量浓度突增,削弱了太阳紫外辐射强度,O_3质量浓度开始下降。此后,在低压槽作用下PM_(2.5)质量浓度增到峰值,O_3质量浓度保持下降趋势。9月5—7日形成了3 d的O_3与PM_(2.5)复合污染事件。

Analysis of a near earth surface O3 and PM2.5 pollution in combination with its contaminating process in Beijing

The present paper has its goal to bring about an analysis of a near earth surface O3 and PM2.5 pollution in combination with its contaminating process in Beijing based on the analysis of the monitoring data of O3,and PM2.5,and the analysis of the solar ultraviolet radiation and meteorological factors.It has also aimed at making a simulated research for a near-surface O3 and PM2.5 combined air pollution process in Beijing from Sept.3 to 8,2014,with the atmospheric environment background field study with the WRF model.The results of our research show that the high level O3 and PM2.5 pollution tends to be related with the successive observation and continuous control of the continental high pressure and the subtropical high pressure system.For it is the strong solar ultraviolet radiation combined with the downdraft resuited high pressure that has contributed to the main boundary layer combined pollution,especially,the O3 pollution.It is just in this O3 and PM2.5 combined pollution process that has promoted the daily average concentration of O3 beyond its maximum limit for the successive four days from Sept.4 to Sept.7,and then exceeded the limit for another three days from Sept.5 to 7 with the daily average concentration of PM2.5 beingkept at that level.The reason for such a phenomenon is that by the successive and continuous control of the continental high pressure and the subtropical high system pressure,it keeps continuously fine and sunny days in Beijing,in which situation,the solar ultraviolet radiation remains intense with the ground wind field being weak.Therefore,in such a meteorological situation,it was possible for the atmosphere to keep a persistent downward trend below 700 hPa.And,so,the daily average O3 concentration can go on increasing day by day till the peak value on Sept.5,with the PM2.5 average concentration simultaneously going up day by day.Furthermore,due to the influence of transfer of the warm wet airflow from the south to the western edge of the subtropical high and adverse inversion formed by the southern airflow,PM2.5 concentration may take chance to increase suddenly on Sept.6,which has in turn slackened the intensity of the solar ultraviolet radiation,so as to make the concentration of O3 declining.After that,the PM2.5 concentration may increase to the peak value under the influence of the low-pressure trough and keep the O3 concentration downwardly declining.Thus,the O3 and PM2.5 mixed pollution incident has thus been maintained from Sept.5 to 7 for the three consecutive days.