Study On Heavy Metal And Polycyclic Aromatic Hydrocarbon Pollution In Fine Particle Dust On Roads In Datong City In Spring And Summer

Fine particle dust on urban roads is the source and sink of heavy metals and polycyclic aromatic hydrocarbons(PAHs)in the city.It is an important hub of heavy metals and polycyclic aromatic hydrocarbons migration in the multi-environmental interface,and an important medium to systematically understand the urban environmental quality.Diachronic sampling is the basis for studying the dynamic change of heavy metal and PAH pollution characteristics,which is helpful to reveal the migration and transformation laws of heavy metal and PAH in different natural environments,and provide scientific support for in-depth analysis of urban environmental pollution mechanism and theory.In this study,Datong,a typical coal resource-based city,is taken as the research area,in which a total 188 road surface dust samples were continuously collected in spring and summer at the road intersection,and all the dust samples were sieved to 63 μm size particles,which size is taken as a representative research medium for its premium physical and chemical characteristics.Characteristics of heavy metals and PAHs in the samples are analyzed,covering the physical and chemical characteristics,spatial distribution,source characteristics,risk characteristics,pollution characteristics and other environmental conditions of.Meanwhile in-depth research has also been carried out on the correlation mechanism.The understandings and conclusions concerning have been achieved as following:(1)In spring fine-grained dust samples from Datong City,the average contents of Mn,Ni,and V exceeds the background values of the corresponding elements in the soil of Shanxi Province.The geoaccumulation index of Cu,Pb,and Zn reach to mildly-polluted level,Mn and Cr reach to moderately-polluted level,and the index of Co,Ni and V show gotten uncontaminated.In summer samples,the average content of Cu,Pb,Zn,Cr,Co,Mn,Ni,and V also exceeded the background value of corresponding element in local soil.The geoaccumulation index of Co,Pb,Zn,and Cr is shown at mildly-polluted levels,the remaining 4 elements are unpolluted.The average content of most elements in the spring sample is higher than the average contents of corresponding element in the summer sample,and the average value of the geoaccumulation index of Pb,Zn,and Cr in the spring sample is higher than that of the corresponding element in the summer sample respectively,while the geoaccumulation index value of Co in the summer sample is higher than in spring samples.It shows that in Datong the accumulation leve of heavy metals in spring fine particles is higher than that in summer,but some elements are opposite,which may be related to different sources of heavy metals in fine particles in spring and summer.(2)The pollution load index of heavy metals in 94 dust samples collected during spring shows that the comprehensive pollution load index of all heavy metals was within 1.05 and 2.75,indicating that all spring samples from Datong are moderate-intensively contaminated by heavy metals.Among the 94 summer samples,92%of the samples get a moderate pollution load index,2%of the samples reached at the level of intensively-polluted level,and the remaining samples were uncontaminated.The ecological risk assessment results on Datong City show that the ecological risk index of Pb in fine dust in spring is 14.62,which means medium potential ecological hazards,and the ecological risk indices for the remaining heavy metals are:Cu(9.00),Zn(3.00),Mn(1.14),Cr(4.41),Co(7.46),Ni(5.83),V(2.74);the potential ecological risk index Pb in summer is 10.08,which has a medium potential ecological hazard.The ecological risk indexes of other heavy metals are:Cu(5.98),Zn(2.19),Mn(1.00),Cr(4.31),Co(5.51),Ni(4.63),V(2.59),In general,the heavy metal pollution and the potential ecological risk intensity of fine-grained dust in Datong are higher in summer than in summer,and the environmental pollution degree in spring is higher than in summer.(3)The content range of PAHs in 94 samples of road dust in spring is 3.584-86.210 mg/kg,the average content is 13.538 mg/kg.The content range of PAHs in 94 samples collected in summer is within 1.705-32.764 mg/kg,the average content is 12.656 mg/kg;Results of single factor pollution assessment of PAHs in spring samples:Nap,Phe,BbF,BkF,BaP and Pyr are of high pollution level,BaA and IcdP are of medium pollution level,and dbaha is of high pollution level as a whole Pollution level;in summer samples,single factor pollution assessment of PAHs:Nap,BbF and BaP are of high pollution level,Phe,DBahA and Pyr are of high pollution level,BaA,IcdP and BkF are of medium pollution level.On the whole,the PAHs content and pollution level in spring are higher than that in summer,which may be due to the hot summer weather and higher temperatures,which makes polycyclic aromatic hydrocarbons more volatile,resulting in the average PAHs content in the fine dust in spring is higher than that in summer,and the pollution level is also relatively higher than that in summer.(4)The results of spatial distribution of heavy metal content show that the high value areas of Co,Ni,Pb and V in the dust in spring were located in the middle of the city,the content of Cu and Zn was higher in the southeast than that in the northwest,while the content of Cr and Mn was evenly distributed.In summer dust,the high value areas of Pb and V are located in the middle of Datong City;the high value areas of Co are located in the middle and northwest of the city;the high value areas of Cr and Mn are located in the West and north of the city,and the content decreases from northwest to southeast;the uniform distribution of Cu,Ni and Zn does not have the obvious high value areas.In spring,the content of heavy metals is high in the middle and southeast of Datong City,and low in the northwest;in summer,the content of heavy metals is high in the middle and northwest,and low in the southeast.(5)The spatial distribution of PAHs content is mainly as follows:In spring,the content of 2-ring PAHs is the highest in the middle and southwest of the city,and the south is the low value area;the content of 3-ring PAHs is the typical high in the south and low in the north;the distribution of 4-ring PAHs is uniform;the high value area of 5-ring PAHs is the middle and East,and the content decreases in turn around;the east of 6-pahs is the high value area,and the north is the low value area.in summer,the content of 2-ring PAHs in the northwest and southeast of fine-grained dust is the highest,3-ring PAHs in the northwest and 3-ring PAHs in the middle,4-ring PAHs,5-ring PAHs and 6-ring PAHs in the middle of Datong City are the highest,and the content in the East is the lowest.In spring,the content of most PAHs is high in the middle,East and north of Datong City,but the content of 2-ring PAHs is the highest in the southwest of Datong City.In summer,the content of PAHs is high in the northwest,middle and east of Datong City,and low in the East.(6)Positive definite matrix factor analysis(PMF)and PCA are used to analyze the sources of heavy metals in fine-grained dust of Datong City in spring and summer.The results show that the four heavy metals of Mn,Co,Ni and V in fine-grained dust of Datong City in spring are from natural sources,Cu,Zn and Cr are mainly from traffic activities,Pb is from coal combustion and automobile exhaust emissions,etc.;Mn,Co,Ni and V in fine-grained dust of Datong City in summer V heavy metals also come from natural sources,Pb and Cu mainly come from the wear of auto parts and tires,Zn and Cr mainly come from industrial and traffic emissions.(7)Two methods are used to identify the source of PAHs in spring and summer samples:1)LMW/HMW ratio method.The results show that PAHs in Datong City in spring and summer are mainly from incomplete combustion and oil leakage of various fossil fuels under low and medium temperature conditions,and a small amount from high temperature combustion of fossil fuels.2)The source calculation results of Icd/(Icdp+Bghip)and baa/(BaA+CHy)show that PAHs in the samples mainly come from incomplete combustion of petroleum and fossil fuels.The results of source recognition by two different feature ratio methods are basically the same.