石家庄市一次大气重污染过程的边界层特征和成因分析

针对石家庄市2015年12月5—14日出现的重污染过程,利用石家庄市逐日地基微波辐射计、风廓线雷达、地面气象观测资料以及同期的污染物观测资料,分析了重污染过程期间大气边界层温度、湿度、风变化特征及对PM_(2.5)的影响,采用Hysplit后向气团轨迹模式对污染来源进行分析。此次重污染以局地排放为主要形成源,期间冷空气势力弱,地面日平均风速均在1.5 m/s以下,日平均相对湿度均在70%以上,风速小、湿度大,稳定的大气环流形势为重污染提供了持续稳定的大气环境背景。逆温形成及快速增厚导致重污染开始,逆温层平均厚度为683 m,逆温层厚、强、不易消散,导致重污染持续时间长、污染重。近地面小风层厚(平均700 m左右),通风能力弱,导致污染物难以稀释扩散。同时近地层湿度大、厚度厚,使得PM_(2.5)更容易形成和积累,对重污染加重起到了促进作用。

Formation Mechanism and Boundary Layer Meteorology Characteristic of a Serious Pollution in Shijiazhuang

The temperature and humidity and wind change of the atmospheric boundary layer and its impact on PM2.5 for the severe pollution event during December 5-14, 2015 were studied with daily observation data from ground-based microwave ra-diometer, radar wind profiler, meteorological station and air pollution observation station, respectively. In this paper, the pollution forming source was analyzed with the Hysplit model. The results showed that local pollutant emission was the main pollution forming source during the severe pollution. The cold air was weak, the mean wind speed was less than 1.5m/s and relative hu-midity was more than 70% during the sustained fog-haze event. The weather background of weak breeze, abundant humidity and stable atmosphere circulation was favorable for the formation of serious pollution. The beginning and increasing in inversion layer thickness caused the pollution formation. The average height of inversion layer was about 700m. And the severe and long-lasting fog-haze event was attributed to the thick, strong and long-lasting inversion layer. The small wind layer thickness near ground was high (average 700m) and the ventilating capacity was weak, resulting in difficult dilution and diffusion of pollutants. In addition, high humidity and humidity layer thickness made it easier for PM2.5 to form and accumulate, and it also contributed to the beginning and increasing severe pollution.