Pollution Characteristics,sources And Risk Assessment Of Heavy Metals In PM_2.5 In Typical Coking Polluted Areas

The frequent occurrence of haze events in recent years was mainly due to the high concentration of fine particulate matter(PM_2.5)in the atmosphere.PM_2.5 is a kind of compound pollutant composed of many kinds of pollutants.Although the content of heavy metal elements in PM_2.5 is relatively small,when they enter the body with PM_2.5 through breathing,they can still cause important harm to human health,so it got a lot of attention.However,at present,the related research mainly concentrated in the developed cities and the regions,paied less attention to the industrial agglomeration area.In order to understand the pollution characteristics,main sources and potential ecological and health risks of heavy metal elements in PM_2.5 in the atmosphere of typical coking pollution areas in the central area of Shanxi province,the distribution characteristics of coking industry are clustered,in this study,a sampling site was set up in Jiexiu,a representative city of this type of region,and a background site was set up in the agricultural area of Fangshan as control.The PM_2.5 samples were collected in four seasons from 2016 to 2017,eleven heavy metal elements（V,Cr,Mn,Co,Ni,Cu,Zn,As,Cd,Sb and Pb）were analyzed,its source was discussed by using enrichment factor method,correlation analysis method,and analyzed qualitatively and semi-quantitatively by principal component analysis（PCA）and positive definite matrix factor analysis（PMF）.Then,the regional sources of each pollution source factor from PMF model were discussed by using potential source contribution factor analysis model（PSCF）,the potential ecological and health risk assessment model was used to evaluate the hazard.The main conclusions of this study are as follows:（1）The daily average concentration of PM_2.5 in Jiexiu was as high as 205.35μg/m³,which was 2.74 times of the second-order average concentration limit（75μg/m³）of Chinese ambient air quality standard,and was much higher than that in Fangshan（48.32μg/m³）.PM_2.5 concentrations in Jiexiu and Fangshan were higher in autumn and winter than in spring and summer,autumn and winter were related to coal combustion,Jiexiu was affected by secondary transformation,the concentration in summer was higher than that in spring,and the concentration in Fangshan was higher than that in summer,it was probably the same Some Random Place Somewhere as Fangshan,with a lot of dust in spring.（2）The concentrations of 8 heavy metals（Mn,Co,Cu,Zn,As,Cd,Sb,Pb）in PM_2.5 in Jiexiu were higher than those in Fangshan,the concentrations of Pb,Cd,Zn,Mn and As were 14.82,9.30,8.11,6.91 and 6.67 times of those in Fangshan respectively.The concentrations of Zn,Pb,Mn,Cr,Cu and As were43.18%,33.98%,10.42%,5.63%,2.89%and 2.16%,respectively,while the concentrations of Cr,Zn,Pb,Cu and Mn were more than 2%in Fangshan,the percentages were 52.22%,20.59%,8.87%,7.22%and 5.83%respectively.（3）The results of enrichment factor method showed that heavy metals Cd,Pb and Zn were heavily enriched（>100）in PM_2.5 in Jiexiu all the year round,mainly contributed by human sources,and Sb,Cr,Cu and As were slightly enriched（10～100）and influenced by human activities,Ni,V and Co were mainly from natural sources（<10）.Except for Cr,the enrichment factors of heavy metals in PM_2.5 in Fangshan were all smaller than those in Jiexiu,and there were no heavy enrichment elements in the whole year.（4）According to the correlation and principal component analysis,the main sources of PM_2.5 in Jiexiu were mixed sources（coal and coking,motor vehicle emission,Dust）,oil combustion sources and metal smelting sources,the contribution rates were 51.67%,14.77%and 9.91%respectively;The main sources of PM_2.5 in Fangshan were coal-fired sources,fugitive dust sources,motor vehicles and transmission sources,with contribution rates of 41.82%,26.39%and 13.59%,respectively.（5）The analytical results of PMF sources showed that the main sources of heavy metals in PM_2.5 in Jiexiu were coal burning and dry distillation sources,motor vehicle sources,fugitive dust sources,metal smelting sources and oil burning sources,the proportion of heavy metals in PM_2.5 in Fangshan was 51.34%,24.04%,11.17%,8.22%,5.23%respectively;the major sources of heavy metals in PM_2.5 were transmission source,coal-burning source,motor vehicle source and dust-raising source,the proportion was 36.09%,30.24%,21.21%and 15.01%respectively.（6）The PSCF model showed that the hot spots of all pollution sources in Jiexiu were concentrated in the local area,mainly in the Taiyuan Basin area,while the hot spots were located in the Lüliang Mountains vein and the Taiyuan Basin,the transmission sources were Yangquan,Zhongyang,Xing County,Shijiazhuang and Yulin.（7）The potential ecological risk level of the two sampling points were extremely strong,and the single-factor risk index of Cd was the largest.The comprehensive ecological risk of Jiexiu was higher than that of other cities in the province.The harm of the same element to human body is children>adult male>adult female,Jiexiu Mn,Cr（children）had non-cancer risk,As,Cr,Pb,Cd,Co（children）had cancer risk,and in Fangshan County CR,there was non-cancer risk,cancer risk for Cr,As and Pb.The results of this study can provide scientific support for the prevention and control of heavy metal pollution in coking polluted areas and provide theoretical basis for the formulation of related policies.