两类污染型下中低空风切变对PM2.5浓度影响

基于2015~2020年京津冀地区生态环境监测数据和多源气象数据,分析了北京地区0~3km中低空垂直风切变在不同PM_2.5等级下的演变特征。结果表明,风速日变化特征随着PM_2.5浓度升高而逐渐减弱,PM_2.56级污染时近地面风速日变化基本消失,甚至反向变化;白天边界层风速增大时段对应10m/(s·km)以下的风切变,20:00后增大至12~14m/(s·km),该现象随着PM_2.5污染加重变得更为显著,白天时段近地层垂直风切变较小值(<6m/(s·km))维持,可能是污染严重的信号之一;基于旋转经验正交函数分解法(REOF),将污染日下中低空垂直风切变分为无扰动型和压缩型,压缩型低压强度略强于无扰动型,无扰动型的PM_2.5浓度均值、峰值较压缩型更高,逆温强于压缩型,另外,无扰动型PM_2.5浓度增长期和边界层高度(PBLH)反向变化,压缩型PM_2.5浓度增长期和PBLH同向变化。

Effects of vertical wind shear on PM2.5 concentration under two pollution weather types

Based on the ecological environment monitoring data and multi-source meteorological data from 2015 to 2020 in Beijing-Tianjin-Hebei region, this study analyzed the evolution characteristics of 0~3km VWS at different PM_2.5 levels in Beijing. The diurnal variation characteristics of wind speed gradually weakened with the increase of PM_2.5 concentration. When PM_2.5 level 6pollution occured, the diurnal variation of near-surface wind speed basically disappeared or even changed in reverse direction. The VWS below 10m/(s·km) corresponded to the increase of boundary layer wind speed in the daytime which increased to 12~14m/(s·km) after 20:00. This phenomenon became more significant with the increase of PM_2.5, and the VWS near the stratum remains small (<6m/(s·km)) in the daytime could be one of the signs of serious pollution. Based on the rotated empirical orthogonal function (REOF) decomposition method, the VWS was divided into two types which called undisturbed type and compression type. The low pressure intensity of compression type was slightly better than undisturbed type; the PM_2.5 peak and daily value and inversion of undisturbed type were higher than compression type. In addition, the PM_2.5 growth of the undisturbed type and PBLH reverse change and the PM_2.5 growth of compressed type changed in the same direction as Planetary Boundary Layer Height (PBLH).