湘潭市秋季一次大气污染过程分析

利用常规高空和地面气象观测资料、湘潭市空气质量监测数据并结合HYSPLIT4后向轨迹模式对2020年10月28—31日污染天气特征及成因进行分析。结果表明此次污染过程分为3个阶段：第1阶段为北方偏二次型传输阶段，此阶段北风风力较大，在强北风的推动下华北地区污染物(PM_2.5)向南传输影响湘潭；第2阶段为大气高湿静稳条件下本地源(工业源、移动源、扬尘源、生物质燃烧源)排放累积阶段，此阶段地面转均压场，整层大气湿度接近饱和并出现弱降水，气态污染物在污染过程中发生二次转化，颗粒物吸湿增长，且近地面出现逆温，不利于污染物的垂直扩散，导致边界层内的污染物不断累积，污染加重，推高了湘潭的PM_2.5浓度峰值；第3阶段为污染物缓慢清除阶段，随着新一波冷空气影响湘潭地区，水平扩散条件逐步改善，且上游空气质量优良，本地污染物得到有利扩散，此次污染过程结束。

Analysis of an Air Pollution Process in Xiangtan City during Autumn

Based on conventional upper air and ground meteorological observation data, air quality monitoring data of Xiangtan city and HYSPLIT4 backward trajectory model, the characteristics and causes of polluted weather from October 28 to 31, 2020 were analyzed. The results show that the pollution process is divided into three phases: the first phase is the Northern partial quadratic transmission. In this phase, the northerly wind is relatively strong to promote the transmission of pollutants(PM_2.5) from North China to the south, affecting Xiangtan;the second phase is the accumulation of emissions from local sources(industrial sources, mobile sources, dust sources, biomass combustion sources) under the conditions of atmospheric high humidity and static stability. At this phase, the ground turns to a homogeneous pressure field, the humidity of the whole atmosphere approaches saturation and weak precipitation occurs, the gaseous pollutants undergo secondary transformation in the pollution process, and the moisture absorption of particles increases.There is a temperature inversion near the ground, which is not conducive to the vertical diffusion of pollutants, as a result,pollutants in the boundary layer continue to accumulate and pollution increases, pushing up the peak concentration of PM_2.5;the third phase is the slow removal of pollutants. As a new wave of cold air affects the Xiangtan area, the horizontal diffusion conditions are gradually improved, the air quality in the upstream area is good, and the local pollutants are diffused favorably.,so this pollution process is over.