Study On The Distribution Characteristics Of PM_2.5 Under Different Weather Conditions In The Hilly Area Of Western Zhejiang

This study uses pollution data from the National Control Station in the hilly area of western Zhejiang from 2015 to 2018,GDAS and FNL meteorological data,and observation data from 2018 to 2019,and uses the HYSPLIT model and WRF-CHEM model to provide a basis for weather classification of sea level pressure fields.Above,study the transport path of PM_2.5under different weather conditions in the region in winter,the distribution characteristics of potential source areas,the vertical structure of PM_2.5and the influence of the hilly terrain in western Zhejiang on the transport and diffusion of PM_2.5.The results show that:(1)The winter in the hilly area of western Zhejiang is mainly affected by six weather conditions:high pressure,high pressure front,high pressure bottom,L-shaped high pressure,low pressure and low pressure front.Among them,the average concentration of PM_2.5under the control of high pressure and high pressure bottom is higher.high.The cluster analysis of the air mass trajectory shows that the polluted air masses under the high-pressure and high-pressure front control mainly come from Shandong and Jiangsu,the polluted air masses under the high-pressure bottom and the L-shaped high-pressure control mainly come from Inner Mongolia,Liaoning and other places,and the pollution under the low-pressure and low-pressure front control The air masses mainly come from the central and southeastern regions of Zhejiang.The potential source areas under the control of high pressure are the most widely distributed,located in the southwest,northeast,Shanghai and southeast of Jiangsu,followed by the bottom control of the high pressure,located in the middle and east of Zhejiang,the northeast and the northeast.In the Shanghai area,the potential source areas of the high-pressure front,L-shaped high-pressure,low-pressure and low-pressure front are relatively small,and are basically located in Zhejiang,southern Jiangsu,and Shanghai.(2)The vertical distribution of PM_2.5is different under different weather conditions.(1)When the thermal effect is dominant,in the unstable boundary layer,the PM_2.5concentration under the high-pressure front control decreases slightly at the place where the wind speed increases;under the high-pressure control,PM_2.5decreases slowly with height;under the high-pressure bottom control,PM_2.5The concentration will increase slowly with height;under L-shaped high pressure control,PM_2.5basically does not change with height.In the stable boundary layer,the PM_2.5peak under high pressure front control appears at the top of the temperature inversion layer,and the PM_2.5peak under high pressure,high-low,and L-shaped control appears at a height of 50m.(2)When the dynamic effect is dominant,in the stable stratification,the PM_2.5concentration in the inversion layer under the control of the low pressure front and the high pressure front is basically unchanged,and the PM_2.5concentration in the temperature inversion layer increases rapidly with the increase of wind speed.In the unstable stratification,the larger wind speed controlled by the high pressure front may transport PM_2.5in the vertical direction to the downstream,or transport the pollutants from the upstream area to the local area.(3)The simulation of PM_2.5transportation and diffusion process shows that the influence of hilly terrain on PM_2.5is different under different weather conditions.(1)Under the control of the high-pressure front,the wind speed of the northerly airflow is relatively high,and the terrain obstructs the transportation of PM_2.5around the mountain and slows the speed.(2)Under the control of high pressure,the wind speed of the northerly airflow is relatively small,and PM_2.5will stay inside the hills,mainly vertical diffusion.(3)Under the control of the bottom of the high pressure,PM_2.5accumulates in the northeast and southeast of the hills,and gradually spreads from east to west along valleys and foothills.(4)Under the control of L-shaped high pressure,PM_2.5accumulates in the west and south of the hills and transports eastward along the valley.When blocked by the eastern mountains,it will transport northward along the foot of the mountain.