临汾地区持续性重污染天气过程成因分析

Cause Analysis of a Persistent Heavy Pollution Weather in Linfen Area

利用常规气象资料、NECP再分析资料以及临汾市环境监测中心站的污染物浓度资料,对2019年1月2-14日临汾市区一次持续性重污染天气过程特征及气象成因进行分析,并运用HYSPLIT4后向轨迹模式结合污染物排放清单数据,分析污染过程中的气流输送情况。结果表明:(1)此次持续性重污染天气过程范围广、持续时间长、污染高、强度大,临汾空气污染指数AQI峰值达434,PM_(2.5)/PM_(10)值维持在80%左右,细粒子污染明显;(2)重污染期间,高空环流平直,多短波活动;中低层风速小,多弱辐合出现;地面场上高压底前部弱气压场控制,环流形势为重污染天气的发展维持提供有利气象条件;(3)重污染期间市逆温层层数多且逆温深厚,逆温层厚度与逆温层数成反比,有两层逆温且第一层厚度较厚的层结最不利于空气污染物扩散清除;(4)物理量场上,高层风速减小、中层风场辐合、850 hPa以下以南风为主的小风天气及水汽场上一定范围内的较大湿度有利于颗粒物的累积和吸湿增长;交替出现的正负弱涡度平流随高度的增加或减小所引起的弱垂直运动对污染物的扩散清除不利,其中一定强度的正涡度平流随高度增加引起的上升运动会加剧污染物的水平和垂直输送,使污染严重且层次深厚;(5)污染期间,临汾主要受两条不同的偏西北路、偏西、偏东路4种输送气流的影响;其中,西北路出现频率最大,西路所携带的SO_(2)多。

Based on conventional meteorological data,NECP reanalysis data,and pollutant concentration data from Lin-fen Environmental Protection Bureau,this paper analyzes the weather characteristics and meteorological causes of a per-sistent heavy pollution that took place in Linfen from January 2 to 14,2019.Combined with pollutant discharge invento-ry data,HYSPLIT4 backward trajectory model was used to analyze the air transport.The results are as follows:(1)This pollution weather is characterized by wide range,long duration and high pollution intensity.The peak value of Lin-fen’s air pollution index AQI reached 434.The ratio of PM2.5/PM10 remains around 80%,so it’s clearly fine particu-lates contamination.(2)During the period of continuous pollution weather,the upper circulation is straight and short-wave activity is frequent;the wind speed in the middle and lower layers is small,and there are many weak convergence.On the sea level pressure field,Linfen is in the weak pressure field that at the bottom of the high pressurewhich provides favourable meteorological conditions for the development and maintenance of heavy pollution weather.(3)During the period of pollution,the thickness of the inversion layer is inversely proportional to the number of layers.The stratifica-tion with two inversion layers and thicker thickness of the first layer is the most unfavorable to the diffusion and removal of air pollutants.(4)Physically,the following conditions are conducive to the accumulation of particulate matter and the increase of moisture absorption:decrease of wind speed in the upper layer,convergence of mid-level wind,light windy weather dominated by the south wind in low level,high humidity in a certain range,weak vertical motion and so on.The upward movement caused by positive vorticity advection of a certain intensity with the increase of height could intensify the horizontal and vertical transport of pollutants,resulting in serious and deep pollution levels.(5)During the period of pollution,Linfen is mainly affected by four kinds of conveying air flow,they are two different northwest roads,west road and east road;Among them,the northwest road appeared the most frequently,and the west road carried more SO_(2).