2018年3月两会期间北京重污染过程边界层气象的演变分析

为研究北京冬季重污染过程的污染特征及成因，采用边界层风场、温/湿场和气溶胶垂直探测等雷达综合遥测手段，对2018年3月北京两会期间的一次典型重污染过程，从边界层气象要素演变进行综合研究.结果表明:①整个污染过程历时7 d，轻度以上污染时数达118 h（占污染过程总小时数的69.8%），严重污染时数达16 h（占污染过程总小时数的9.5%），ρ（PM_2.5）最高达333.5 μg/m3.②从气溶胶的垂直空间演变来看，重污染天气的形成，除受本地源排放积累的影响外，还存在北京南部和东部的外部污染传输.贴地或上部逆温的稳定温度层结基本上对应ρ（PM_2.5）的累积过程，其中，重污染时段逆温维持达68 h，逆温层厚度为500~1 100 m，最大平均逆温强度为0.6℃/（100 m）.大气边界层高度偏低（积累过程白天在1 000 m以下，夜间只有300~500 m），导致污染物持续积累.整个污染过程中，高湿时段引起PM_2.5吸湿增长和转化加重了污染程度；近地层持续小风导致污染积累；西南、东或东南方向大风层（10 m/s左右）向低空下探，有利于污染的缓解；强西北风或北风作用，使污染得以清除.研究显示，污染过程与边界层气象要素的演变密切相关. 

Meteorological Evolution of Boundary Layer during Heavy Pollution in Beijing during the CPPCC (China People's Political Consultative Conference) in March 2018

In order to study the characteristics and causes of heavy pollution in winter in Beijing, a typical heavy pollution process during the CPPCC (China People's Political Consultative Conference) in March 2018 was studied using radar remote sensing techniques such as boundary layer wind field, temperature/humidity field and aerosol vertical sounding. The results show that:(1) The pollution lasted for 7 d, including 118 h (69.8%) of slight pollution, 16 h (9.5%) of serious pollution, and the maximum pollution was 333.5 μg/m3. (2) The evolution of the pollution process is studied using the vertical observation equipment such as wind, temperature, humidity and aerosol. From the vertical spatial evolution of the aerosol, the formation of heavy pollution, in addition to the influence of the local source, has the external pollution transmission in the south and east of Beijing. The stable temperature layer of ground or upper temperature inversion is basically corresponding to the accumulation of PM_2.5 on the ground, in which the time of severe pollution is 68 h, the thickness is 500-1100 m, the maximum strength is 0.6℃/(100 m). The height of atmospheric boundary layer is low (the accumulation process is below 1000 m in the daytime and only 300-500 m at night), which leads to the continuous accumulation of pollutants. The near ground layer maintains a small wind and accumulates pollution; the high wind speed layer (about 10 m/s) in the southwest, east or southeast directions goes down to low altitude, which mitigates pollution, and the strong northwest wind or the north wind usually makes the pollution clear. The results show that the pollution process is closely related to the evolution of the meteorological elements in the boundary layer.