Analysis Of The Persistent Pollution Events In The Yangtze River Delta During The Winter Of 2014—2017 And The Impact Of The Synoptic Pattern On Persistent Pollution

In this paper,air pollution monitoring data from the Ministry of Environmental Protection and NCEP/NCAR reanalysis during 2014—2017 were used to investigate the impacts of large-scale circulation pattern and the associated meteorological parameters on the winter persistent pollution events in the Yangtze River Delta.Main conclusions are as follows:1、During the winter of 2014—2017,a total of 19 persistent pollution events occurred in the Yangtze River Delta region,including 5 persistent heavy pollution events,especially in.December and January.The daily variation of PM_2.5 concentration showed a good consistency with that of 2-m temperature,but an inverse correlation with planetary boundary layer height.When the source of pollutants in the Yangtze River Delta was transported over long distances at the beginning of the pollution process,the near-surface wind speed first increased and then decreased;when the source of the pollutants was local accumulation,the near-surface wind speed kept at a low level.In both cases,the wind speed increased significantly at the later stage of the pollution event,which led to a rapid decrease in PM_2.5concentration.2、On the day of severe pollution,the relative humidity in the Yangtze River Delta region increased abnormally,and the height-longitude temperature anomaly was abnormal.The warm layer is not conducive to the diffusion of pollutants.In the Yangtze River Delta,the tropospheric middle layer is affected by the abnormal positive pressure change.The contour is flat and the cold air activity is weak.In the lower troposphere,it is mostly controlled by the pressure equalizing field or located on top of the high pressure.As a result,severe pollution incidents broke out.Frequent cold air activities and strong East Asian winter monsoon have a positive effect on the occurrence of persistent and severe pollution events in the Yangtze River Delta.3、At the beginning of many continuous and severe pollution processes,the movement of the cold front from north to south transported pollutants to the Yangtze River Delta,causing the PM2.5 concentration in the Yangtze River Delta to increase.In the later stage of the persistent severe pollution incidents,the cold front transit process will occur.At this time,the Yangtze River Delta area is affected by the strong cold air after the cold front transits.The strong wind accompanied by the strong cold air will remove the pollutants in the Yangtze River Delta area,making PM_2.5 the concentration decreased rapidly.