Study On Characteristics Of Seasonal Air Pollution And Causes Of Typical Pollution Processes In Winter And Summer In Wenjiang District

As the national economic and social development accelerates during China’s 13th Five-Year Plan period,the characteristics of air pollution in China have changed significantly,from the traditional soot-based pollution to the various emissions from automobile exhaust and dust and industrial processes,dominated by the fine particles and ozone pollution.Based on the data related to air pollutant mass concentration and ground meteorological factors,this study integrates statistical analysis methods,characteristic radar map and potential source analysis to explore the seasonal pollution characteristics of Wenjiang District from 2016 to 2020.The typical pollution processes in winter and summer are firstly classified,and then combined with WPSCF and WCWT analysis to investigate the external causes of pollution process formation.Finally,the emission inventory system of local anthropogenic sources of PM_2.5and VOCs in Wenjiang District is established to elucidate the endogenous causes of polluted weather.The main conclusions are as follows:（1）Significant seasonal air pollution characteristics was observed in Wenjiang District during the study period,with the best air quality in autumn and spring,followed by summer,and winter.During 2016-2020,the proportion of fine particulate matter pollution in the spring of Wenjiang District decreased significantly,from 60.3%in 2016 to 18.3%in2020,while the proportion of O₃pollution increased by 50.3%.The most serious ozone pollution was found in summer,with the proportion increased from 80.5%to 98.4%.The proportion of good weather in autumn increased by 29.2%,still dominated by particulate matter.The proportion of winter pollution declined 30.1%,still with the high air quality index,and the proportion of air pollution by fine particulate increased year by year.（2）The changing trend of meteorological factors remained steady during 2016-2020.For,we found the higher the wind speed the stronger the dilution particulate concentration,while when precipitation is not sufficient,high concentrations of water vapor can condense on the surface of particulate matter to form droplets,leading to difficult diffuse particulate matter and further higher concentrations.When the humidity rises to more than 90%,rainfall cansignificantly reduce the concentration of particulate matter.When the wind speed increases,the concentration of gaseous pollutants decreases due to the enhanced diffusion capacity of the atmosphere,while due to the atmospheric motion,the transport of pollutants between surrounding areas,O₃is affected by the input of foreign sources,and its concentration increases with the increase of wind speed in a certain range.（3）In winter,21 pollution events with PM_2.5as the primary pollutant in Wenjiang District during the study period were observed.These events were accompanied by lower wind speed,which made the horizontal diffusion ability decrease and the accumulation of pollutants;high humidity conditions also promoted the transformation of gaseous precursors to secondary particulate matter.In 2017,PM_2.5emissions in Wenjiang District were mainly from the chemical raw materials manufacturing industry（102.67t,82.1%）,manufacturing industry（102.67t,82.1%）.In addition to local sources,Chongzhou,Pidu and Dayi also exacerbates the pollution of PM_2.5in Wenjiang District.（4）A total of 13 pollution events with O₃as the primary pollutant occurred in summer in Wenjiang District during the study period,showing an increasing trend,mainly due to the higher temperature and less rainfall under low humidity conditions.The clear days enhancing the efficiency of photochemical reactions for secondary transformation of O₃.Anthropogenic source emissions of O₃precursors VOCs in Wenjiang District mainly originated from rubber and plastic products（6101.34t,80.3%）and agricultural and food processing industries（998.60t,13.1%）,followed by solvent use sources in wooden furniture coating（337.64t,54.9%）.In addition to local anthropogenic sources,Meishan and Deyang are the main potential sources of pollution transmission and counties such as Shuangliu,Wuhou,Pujiang,Pidu and Xinjin also exacerbates the pollution of O₃in Wenjiang District.