The Pollution Characteristics And Influencing Factors Of Secondary Components In PM_2.5 In Jinan City

Compared with the previous studies,most of them focus on the pollution characteristics of PM_2.5secondary components,but the research on the mechanism and influencing factors of PM_2.5secondary components is relatively less.And Jinan is one of the 2+26 channel cities of Beijing Tianjin Hebei,the traffic is important,and the pollution situation is complex.Therefore,the research on the pollution characteristics and mechanism of PM_2.5and its secondary components in Jinan is of far-reaching significance for the prevention and control of secondary component pollution in the city.In this study,PM_2.5samples from spring(March 16-31,2019),Sandstorm season(may 16-25,2019),autumn(October 15-24,2019)and winter(December 17-2020)in Jinan City were collected in this study.Environmental samples of clean control point,urban rural Integration Department and typical industrial zone were collected simultaneously.The concentrations of SO₄^2-,NO₃^-and NH₄⁺were obtained by ion chromatography.The concentrations of OC(organic carbon)and EC(elemental carbon)were obtained by thermoluminescence carbon analysis.The conclusions are as follows:(1)PM_2.5pollution in Jinan mainly concentrated in autumn and winter,and PM_2.5concentration increased significantly in winter,and there were two severe pollution periods.The growth trend of NO₂and SO₂in winter is similar to that of particulate matter.It may be due to the increase of NO₂and SO₂concentration,which promotes the formation of secondary components SO₄^2-,NO₃^-and NH₄⁺,which leads to the increase of particle concentration.Meanwhile,in the process of two severe pollution,the atmospheric boundary layer(PBL)is greatly reduced,and both of them are in low temperature and high humidity environment,which is not conducive to the diffusion of pollutants.Therefore,the severe pollution in winter is the joint action of gaseous precursor and air environment.The concentrations of NO₃^-and NH₄⁺were winter>autumn>spring>Sandstorm season;SO₄^2-and SOA concentration changed to winter>autumn>Sandstorm season>spring.Comparing the points of Jinan City,clean control point,urban-rural junction and typical industrial zone,it is found that the urban area is the most important point in autumn.In winter,SO₄^2-,NO₃^-and SOA of urban-rural junction are higher than that in urban areas,and SOA concentration in typical industrial areas is higher than that of urban areas.(2)The SOR and NOR in Jinan are greater than 0.1 all year round,so the SO₄^2-and NO₃^-in Jinan mainly come from the secondary transformation.SO₄^2-conversion efficiency was the lowest in spring,0.24,and 0.45 in autumn;NO₃^-was the lowest in Sandstorm season,0.15 and0.25 in autumn.Therefore,the proportion of secondary components in PM_2.5is the largest in autumn.Meanwhile,the concentration of SO₂in Sandstorm season is higher than that in spring and Sandstorm season(0.32)>spring(0.24).However,with the increase of pollution level,the conversion rate of SO₄^2-and NO₃^-increased with the increase of pollution level.When the SOR was heavily polluted,the conversion rate was 0.62,the conversion rate reached the highest,nor was 0.38,and the conversion rate was the highest.The average annual value of[NO₃^-]/[SO₄^2-]in Jinan is 2.005,which indicates that the main PM_2.5pollution in Jinan is mainly from the contribution of mobile sources.The ratio of four seasons in Jinan City was calculated,and the results showed that spring(2.47),Sandstorm season(0.67),autumn(2.57),and winter(1.98).Thus available,Jinan sandstorm season as a fixed source contribution based,the other three seasons mainly in mobile source contribution based..(3)The correlation between the secondary components of the air pollutants is calculated by SPSS.The results show that the main influence of the air pollutants on the secondary components is as follows:the three meteorological factors only have a great influence on SO₄^2-,NO₃^-and NH₄⁺;the temperature only has an influence on OC1,EC1 and EC2;the humidity only has an effect on OC1,oc2 and EC1;the meteorological factors have no correlation with SOA.(4)The results of ISORROPIA thermodynamic model show that the water content will increase with the increase of pollution,the acidity and water content will affect the transformation mechanism of secondary inorganic components,and acidity will inhibit the formation of secondary inorganic components,and acidity will promote the formation of secondary components.Forward forward model is used to simulate the acidity,water content and secondary inorganic components under different temperatures and humidity The results show that when the humidity is small,the balance is mainly affected by acidity,while the balance is mainly affected by water content when the humidity is relatively high,and the humidity will increase with the increase of pollution level.PMF is used to analyze carbon component sources in Jinan City and explore the pollution sources affected by SOA.It is found that the contribution degree of carbon components in Jinan mainly affects pollution sources is as follows:biomass combustion and coal-fired sources(47.9%)>road dust sources(27.2%)>vehicle tail gas sources(20.4%)>unknown sources(4.5%).