北京冬季PM2.5重污染时段不同尺度环流形势及边界层结构分析

城市重霾污染事件的发生除排放源内在原因之外,气象条件是最直接的客观外因。本文以2013年2月21~28日北京地区典型细颗粒物(即PM2.5)重污染过程为例,基于颗粒物水平和垂直监测数据,常规及加密自动气象站数据和高时间分辨率风廓线数据,分析了重污染过程中不同尺度环流形势以及边界层结构的变化对细颗粒物重度污染形成、累积和消散的影响。结果表明:弱低压场或弱高压场控制下,局地西南风和东南风输送与北部山区偏北风在山前的汇聚,配合边界层低层顺时针方向的风切变,易发生大气中细颗粒物的爆发性增长;而均压场控制和近地层持续偏南气流输送,配合高层持续稳定的西北风,是污染长时间持续稳步增长的主因。此外,近地层低风速、高湿度和逆温的维持是区域霾污染爆发增长和长时间持续增长的关键气象因素。高压前部的系统性西北大风是污染得以驱散的直接外部动力。

Analysis of Different-Scales Circulation Patterns and Boundary Layer Structure of PM2.5 Heavy Pollutions in Beijing during Winter

The most immediate external objective of urban heavy haze pollution incidents was the weather conditions in addition to the internal reason of emission sources. Based on horizonal and vertical particulate matter (PM) data, conventional and encryption automatic meterological station data, and wind profiler data, the analysis of the influence of changes of different scales circulation patterns and boundary layer structure on the formation, accumulation, and dissipation of heavy pollutions of PM2.5 in Beijing during 21-28 February 2013 was presented. The results showed that, under the control of low or high weak pressure, the gathering of the southwest local wind, southeast transport wind, and north mountain wind, with clockwise wind shears in boundary layer, tended to bring on growth spurts of fine PM. Otherwise, the main cause of long time and steady growth of pollutions was the control of uniform pressure and near-surface south transport wind with high-level steady northwest wind. In addition, the key meteorlogical factor was near-surface low wind, high humidity, and maintaining a temperature inversion to promote and sustain the growth of regional haze pollution. A northwest wind in front of high pressure was a direct external power to disperse pollutions.