Using the near-surface O3,PM2 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 cau-ses of a typical O3 and PM2.5 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 O3 peaks earlier than that of PM2.5.On the 19th,the concentration of O3 is high and lasts for a long time,whereas on the 20th,the concentration of PM2.5 increases,but that of O3 significantly decreases.The stable layer of low wind and high temperature before the Hetao trough provides favorable conditions for the accumulation of O3 and PM2.5 on the 19th.The decrease of boundary layer height and easterly air transport led to the increase of O3 and PM2.5 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 O3 and PM2.5 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 favora-ble meteorological conditions for the rapid accumulation of PM2.5 near the ground.During the period when particu-late pollution was dominant,the main reason for the low O3 concentration on the 20th is the decrease of near-ground solar radiation caused by low temperature and sudden increase of PM2.5 concentration.On the 19th,the high concentration of O3 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 in-crease of PM2.5 concentration.
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