2019年8月太原市一次典型O_(3)和PM_(2.5)污染天气过程成因分析

Analysis of the causes of a typical O_(3) and PM_(2.5) pollution weather process in Taiyuan city in August 2019

选用太原市近地面O_(3)、PM_(2.5)、气象要素、天气形势、NCEP再分析资料、颗粒物激光雷达等资料,结合后向轨迹模式,对2019年8月19—20日太原市一次典型O_(3)和PM_(2.5)污染天气过程特征及成因进行分析。结果表明:此次污染过程O_(3)浓度早于PM_(2.5)浓度达到峰值,19日O_(3)浓度较大且持续时间长,20日PM_(2.5)浓度增大,但O_(3)浓度明显减小。河套倒槽前小风、高温的稳定层结为19日O_(3)和PM_(2.5)的积累提供了有利条件,边界层高度降低和偏东气流输送导致19日日落后O_(3)和PM_(2.5)浓度增大,其后倒槽过境时的地面上升运动、边界层发展使近地面O_(3)和PM_(2.5)污染得到一定缓解,20日冷锋过境后的边界层高度降低及高湿环境为PM_(2.5)在近地层迅速积累提供了有利气象条件。在颗粒物污染占主导期间,气温偏低以及PM_(2.5)浓度突增造成近地层太阳辐射大幅减小是20日O_(3)浓度偏低的主要原因;19日高浓度O_(3)污染主要受东南方向气流影响,20日来自河南中南部的气流及来自内蒙古地区的沙团是PM_(2.5)浓度上升的主要原因。

Using the near-surface O_(3),PM_(2.5),meteorological elements,weather patterns,NCEP reanalysis data,and particulate laser radar data in Taiyuan city,combined with a backward trajectory model,the characteristics and causes of a typical O_(3) and PM_(2.5) pollution weather process occurred from August 19 to 20,2019,in Taiyuan city were analyzed.The results indicate that during this pollution event,the concentration of O_(3) peaks earlier than that of PM_(2.5).On the 19th,the concentration of O_(3) is high and lasts for a long time,whereas on the 20th,the concentration of PM_(2.5) increases,but that of O_(3) significantly decreases.The stable layer of low wind and high temperature before the Hetao trough provides favorable conditions for the accumulation of O_(3) and PM_(2.5) on the 19th.The decrease of boundary layer height and easterly air transport led to the increase of O_(3) and PM_(2.5) concentrations after sunset on the 19th.Subsequently,the upward movement of the ground and the development of the boundary layer during the transit of the trough reduce the O_(3) and PM_(2.5) pollution near the ground to a certain extent.After the transit of the cold front on the 20th,the reduced height of the boundary layer and the high humidity environment provide favorable meteorological conditions for the rapid accumulation of PM_(2.5) near the ground.During the period when particulate pollution was dominant,the main reason for the low O_(3) concentration on the 20th is the decrease of near-ground solar radiation caused by low temperature and sudden increase of PM_(2.5) concentration.On the 19th,the high concentration of O_(3) pollution is mainly affected by the airflow from the southeast direction,while on the 20th,the airflow from central and southern Henan and the sand mass from Inner Mongolia are the main reasons for the increase of PM_(2.5) concentration.