| In recent years,the impact of atmospheric particulate matter pollution on the ecological environment and human health has attracted much attention.Collecting dustfall samples from various functional zones in Xi'an for a total of one year(From July 2017 to July 2018).The dustfall flux,the pollution level of heavy metals and PAHs,the spatial and temporal differences of sources and the reasons were explored,and the relationship with human activities and urban functional zones was analyzed to provide a scientific theoretical basis for urban functional zoning planning and environmental protection.The concentration of heavy metals and]6 PAHs were analyzed by X-Ray fluorescence spectrometerand high performance liquid chromatography(HPLC),respectively.The composition characteristics,pollution level,spatial distribution,source,ecological and health risk of heavy metals and PAHs,as well as the relationship between PAHs and other indicators(such as TOC,particle size,physical and chemicals,air pollution routine analysis indicators)were analyzed.The main conclusions are as follows:(1)The monthly dustfall flux in Xi'an ranges from 0.29 to 2.42 g·d-1·m-2,with an average of 1.12 g·d-1·m-2.The precipitation fluxes of heavy metals and PAHs were estimated from the atmospheric dustfall fluxes in different functional areas.The average contents of heavy metals Co,Zn,Ni,Cr,Cu,Pb,As and Mn in the dustfall of Xi'an were 27.01,522.98,34.12,103.43,65.44,120.24,12.70 and 569.34 mg/kg,which were 2.5,7.5,1.2,1.7,3.1,5.6,1.1 and 1.02 times of the background values of Shaanxi soil,respectively.Among the functional zones,the content of Cr was the largest in industrial areas,with an average content of 144.06 mg/kg.The content of Pb was the largest in commercial areas,with an average content of 7.2 times that of background value;the content of Co was the largest in residential areas,with an average content of 39.60 mg/kg.The content of Mn,Zn,Ni and Cu in cultural and educational areas and the content of Zn and Pb in tourist areas are relatively high,with the average content of Mn in cultural and educational areas being 667.50 mg/kg,which was higher than that in other areas.The content of As was low in residential areas,but there was no significant difference among other functional areas,ranging from 12.00 mg/kg to 17.00 mg/kg.Using ArcGIS spatial interpolation technology,the spatial distribution characteristics of different heavy metal average contents were studied.It was found that the contents of Ni and Cr in dust fall in suburbs were higher than those in urban areas,while the contents of Pb,Cu and Zn in central urban areas were relatively higher,and the contents of As and Mn in northern areas were significantly higher than those in southern areas.In the seasonal and monthly variations,the eight heavy metals did not change much as a whole,and there was no magnitude change.(2)The total concentrations of sixteen PAHs ranged from 0.92 mg/kg to 27.58 mg/kg,with an average content of 8.60 mg/kg.The maximum content of 16 PAHs was located in Baqiao Thermal Power Plant in the industrial area,and the minimum content was located in Nanhu Lake in the tourist area.The contents of seven carcinogenic aromatic hydrocarbons ? 7CPAHs ranged from 0.25 to 11.30 mg/kg,an average content of 30.85%.Among the functional zones,the content of PAHs in industrial zones was much higher than other functional zones.In seasonal and monthly variations,the fluctuation of the overall level was not significant.The spatial distribution characteristics of PAHs showed that the PAHs content in suburban dustfall was significantly higher than that in central urban area.Especially in the eastern and western industrial intensive areas,from the easterm and western suburbs to the central urban areas,PAHs content showed a decreasing trend.The content of PAHs in the south and north was relatively lower.Spatial evolution of PAHs content in Dustfall in each season showed that PAHs content in eastern industrial zone and central urban area did not change much and that rln eastern region higher,middle region lower.PAHs content in western industrial zone was higher in summer and lower in spring.(3)Heavy metals in the dustfall of Xi'an City were affected by human disturbance to varying degrees.The pollution assessment of Ground Accumulative Index shows that Co,Zn,Cr,Cu and Pb were all polluted.The average Ground Accumulative Index of heavy metal Zn was the largest which belongs to heavy pollution.Co and Cr were slightly polluted.Cu and Pb were moderately polluted.Zn in industrial and tourist areas was heavily polluted.Zn and Pb in commercial and cultural and educational areas were heavily polluted.Zn,Co and Pb in residential areas were moderately polluted.The Geoaccumulative Index of heavy metals also varies in different seasons and months.The Pollution Load Index shows that theindex was between 1.2 and 2.7,which indicates that the pollution of heavy metals of dustfall in Xi'an is in a moderate or moderate degree.The load intensity of cultural and educational areas was the largest.The Pollution Load intensity in winter and spring months was obviously higher thanother seasons,especially in the south region.The composition of PAHs shows that the proportion of PAHs ofdustfall in Xi'an City was higher in the low ring(2-3 ring)and the middle ring(4 ring),and larger in the three ring and the four ring PAHs.The proportion of PAHs in different seasons and months varies among the functional areas.(4)Heavy metal risk assessment shows that heavy metals Zn and Pb may had high potential ecological risk,and the cultural and educational areas in winter had higher ecological risk,which should be paid attention to.The Health risks showed that the non-carcinogenic and carcinogenic risks of heavy metals were lower or no.PAHs risk assessment showed that PAHs in dustfall had moderate or higher potential ecological risk.The concentration of TEQoap based on BaP ranged from 0.07 to 4.01 mg/kg,with an average content of 1.38 mg/kg.PAHs of 16 monomers exceeded ERM in varying degrees,and 2-3rings PAHs and 4-6rings PAHs accounted for a large proportion of samples exceeding ERM.In the evaluation of Life-long Cancer Risk Incremental model,PAHs had a tolerable carcinogenic risk for children and adults,and there was no health impact.(5)The sources of heavy metals and PAHs in Xi'an dustfall were analyzed by Principal Component Analysis and Positive Definite Matrix Factor Analysis.The results showed that the heavy metals in Xi'an dustfall mainly came from traffic activities,industrial sources such as coal combustion and natural sources.Among them,the contribution rate of traffic activity source was the highest(48.18%),followed by industrial source and natural source,which were 28.46%and 23.36%,respectively.The contribution rate of different heavy metals sources was also different.The analysis of PAHs sources of dustfall in Xi'an shows that the main sources was traffic activities,with a contribution rate of 39.7%,followed by fossil fuels and oil spills,coal combustion and low temperature combustion,with contributions of 25.4%,19.4%and 15.5%,respectively.In each season,the contribution rate of traffic activity source was higher,and the contribution rate of coal combustion was relatively higher in winter and springseason.(6)In exploring the influencing factors of heavy metals and PAHs in dustfall,the results of correlation analysis show that there were correlations between PAHs,heavy metals and other indicators.Among them,Cr had good correlation with TOC and TC,Zn had strong correlation with magnetic susceptibility(FD),and Cr,Cu,Pb and As had good correlation with dust deposition subsidence.There were good correlations between various PAHs monomers and different heavy metals,TOC,sedimentation flux,atmospheric particulate matter(PM2.5 and PM10),SO2,NO2 and CO,which may affect the content of heavy metals and PAHs in the atmospheric dust in Xi'an. |
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