Analysis On The Causes Of PM_2.5 Pollution In Winter In Dazhou City

Based on the air quality monitoring data,meteorological monitoring data,environmental statistics data,fine particle filter membrane sampling and analysis data of Dazhou City,the air quality status,pollution meteorological characteristics and pollutant emission characteristics,emission reduction scenarios and a heavy pollution process in winter of Dazhou City were analyzed by using statistical methods and WRF-SMOKE-CMAQ model.The research results show that first,the excellent and good air quality rate of each station in the main urban area of Dazhou city is 66%⁷4%,and the annual average value of PM_2.5.5 is 51⁵9?g/m³.,which does not reach the limit value of ambient air quality standard.The northeast of the main city is less polluted than the southwest and PM_2.5.5 is the most serious pollutant in Dazhou.Second,in Dazhou,the average temperature in 2016 is 18.66°C,the relative humidity is 75.22%,the horizontal visibility is 15021 m,the wind speed is 1.42 m/s,the total precipitation is 1128.5 mm.and the dominant wind direction is due east.The correlation coefficient between average daily wind speed and average daily PM_2.5concentration is-0.528,which is the meteorological factor with the greatest influence on PM_2.5.5 concentration.The greater the wind speed is,the better the diffusion conditions are,and the lower the PM_2.5.5 concentration is.The correlation coefficients of WRF simulated air pressure,temperature,relative humidity and wind speed and observation are 0.991,0.981,0.689 and 0.244,respectively.The former three simulation results are good,but the wind speed simulation results are poor.The results of backward trajectory clustering show that in spring,autumn and winter,in the main urban area of Dazhou,the largest proportion of air mass input receives from the north of Chongqing,which is52.80%,54.23%and 48.75%,respectively,while the main air mass input in summer is not obvious,and its proportion in all directions is the same.Third,in 2016,the anthropogenic emissions of VOCs in Dazhou City were6,7028.8 tons,NH₃ was 6,7864.9 tons,CO was 34,4003.5 tons,NO₂ was 7,7006.4 tons,SO₂ was 5,8667.8 tons,PM_2.5.5 was 6,7094.0 tons,and PM₁₀0 was 19,432.1 tons.The largest sources of NO₂,SO₂,PM_2.5.5 and PM₁₀0 emissions are all industrial combustion sources,accounting for 32.50%,66.00%,50.00%and 64.93%of their total emissions respectively.The largest source of VOCs emission is road mobile source,accounting for 40.01%.The largest source of NH₃ emission is agricultural source,and the main source of NH₃ emission reaching 98%.The main emission sources of CO are road mobile sources,civil coal and metallurgical sources,accounting for 21.49%,23.31%and 27.54%,respectively.Fourth,the effect of CMAQ on PM_2.5.5 simulation in Dazhou city is the best in January,and there is an overestimation in April,July and October.The correlation coefficient between simulation and observation is 0.48.In January,2016,the contribution of PM_2.5.5 from external sources to the urban area of Dazhou was 28.79%by CMAQ simulation.so the joint prevention and control with Kaizhou District and Wanzhou District in the north of Chongqing Municipality should be strengthened.Metallurgical sources,industrial combustion sources and mobile sources contributed19.54%,30.02%and 6%of PM_2.5.5 in urban areas respectively.Fifth,the typical pollution process from January 22 to January 31,2016 in winter was mainly affected by unfavorable meteorological diffusion conditions,such as reduced wind speed and unclear dominant wind direction,as well as local source emissions and chemical reactions.When such pollution was encountered,the regulation and control of reducing emissions from local pollution sources should be strengthened in order to timely alleviate PM_2.5.5 heavy pollution.