Occurrence,Sources And Health Risks Of Polycyclic Aromatic Hydrocarbons In Dry And Wet Deposition In Shanghai

Polycyclic Aromatic Hydrocaebons（PAHs）are typical Persistent Organic Pollutants（POPs）,which are characterized by complex sources,continuous importation,difficult degradation and wide distribution.It is carcinogenic,teratogenic and mutagenic to human body.In 2001,PAHs were included in the Stockholm Convention,and 16 of them have now been included in the US Environmental Protection Agency’s（USEPA）priority control list of pollutants.In recent decades,global climate change has led to a series of changes in atmospheric environment,land use and cover,water environment and water resources worldwide,especially in urban areas.The characteristics of urban environmental pollution have shown a trend of diversification and complexity.Therefore,the ecological environment of the city has become the focus of people’s common concern and the content of multi-disciplinary research.Shanghai is located in the important intersection of the Yangtze River Economic Belt and the core city of the Yangtze River Delta economic circle.With the rapid development of urbanization and social economy,problems such as ecosystem degradation and environmental quality deterioration have appeared in Shanghai,which has become a hot area concerned by many scholars and scientists.In recent years,the status of PAHs pollution in Shanghai is very serious,and the PAHs pollution presents a diversified and complex evolution trend.At present,many scholars have studied the occurrence and sources of PAHs in various media in Shanghai.Dry and wet deposition is the main process of pollutants from the atmosphere to the surface ecosystem.Once the pollutants settle to the surface of land or water environment,they will participate in the biogeochemical cycle of soil erosion,surface runoff and groundwater runoff.These pollutants can be directly absorbed by surface organisms,or transformed and utilized by organisms.Decomposition and transformation of organisms change the physical and chemical properties of pollutants,and their potential toxicity will be transmitted,amplified and enriched through the food web,ultimately affecting human health.Atmospheric particulate matter consists of a mixture of solid and water-based materials that enter the atmosphere through man-made and natural pathways.Carcinogenic polymer PAHs are mostly absorbed in fine particles,posing a serious threat to public health and affecting visibility,climate and ecosystem.PM_2.5 refers to atmospheric particulate matter with aerodynamic diameter less than2.5μm.Compared with larger particles,PM_2.5has a larger specific surface area and is more likely to combine with toxic compounds to cause more serious threats to human health,among which polycyclic aromatic hydrocarbons（PAHs）are important toxic components of PM_2.5.In this study,24 dry deposition samples（12 in urban and 12 in suburban）and 110wet deposition samples（51 in urban and 59 in suburban）were collected in Shanghai city by APS-3A samplers from July 2020 to June 2021.The concentration and component content characteristics of PAHs in these samples were analyzed,the dry and wet deposition fluxes of PAHs were calculated,and the temporal variation,ueban and suburban distribution characteristics of PAHs in dry and wet deposition were revealed,which enriches the real-time data on the pollution status of dry and wet deposition in typical cities.Meanwhile,due to the serious harm caused by the combination of PAHs and PM_2.5,the concentration,component content and seasonal change of PAHs in PM_2.5were analyzed separately,and a large number of domestic and foreign research data were collected and compared to analyze the pollution status.The molecular diagnostic ratios method and Positive Matrix Factorization（PMF）method were used to analyze the source and seasonal variation of PAHs in dry and wet deposition and PM_2.5.At the same time,the HYSPLIT trajectory model was used to simulate the migration path of PM_2.5,and potential source contribution function（PSCF）and concentration-weighted trajectory（CWT）were used to analyze its potential sources.Finally,Health risk of PAHs in dry and wet deposition and PM_2.5 to people of different ages and exposure ways were assessed using incremental lifetime cancer risk model（ILCRs）.This study not only can enrich the data of the pollution characteristics,and provide scientific basis for prevention and control of air pollution in cities,It provides theoretical support for protecting human health and realizing sustainable development of social economy and ecology.The main conclusions of this study are as follows:（1）Concentration range ofΣ₁₆PAHs optimized by US EPA in the annual dry deposition in Shanghai was 0.69～56.43μg/g,average value was 22.5μg/g.The most carcinogenic Ba P monomer was 0.72±0.54μg/g.According to the standard,some dry deposition samples belong to seriously polluted type.The dust flux of the urban sample（112.51mg/（m~2?d））was higher than that of the suburban sample（98.16 mg/（m~2?d））,and the maximum value occurred in the dry season.Flux ofΣ₁₆PAHs in dry deposition was0.11～5.36μg/（m~2?d）,which was higher in dry dry season than rainy season,and urban sample was higher than that of the suburban sample.The total concentration of 7 kinds of PAHs with definite carcinogenicity was 0.41μg/（m~2?d）,About 25%ofΣ₁₆PAHs.（2）Among the 16 monomers of dry deposition PAHs,the order of flux is 2-3 cycles>5-6 cycles>4 cycles.The high molecular weight PAHs flux of urban sample sites is much higher than that of suburbs,because the urban sample sites are located in downtown areas and the traffic flow is larger.A large number of high molecular weight monomers emitted by gasoline and diesel combustion process diffuse in the atmosphere and combine with dust particles,and then settle to the surface.At the same time,the high ring monomer flux increased significantly in winter,which is the result of the increase of coal burning and long-distance transportation in the heating season in northern China.（3）Σ₁₆PAHs concentration in the wet deposition was from 0.16μg/L to 12.36μg/L,with an average of 1.83μg/L.The total concentration range of 7 species PAHs with definite carcinogenicity was 0.19μg/L.The flux ranged from 0.46μg/（m~2?d）to 59.01μg/（m~2?d）,with an average of 13.07μg/（m~2?d）.2～3 rings>4 rings>5～6 rings.At the same time,it is found that the removal rate of PAHs in the atmosphere by wet deposition is much higher than that by dry deposition,and the removal efficiency of wet deposition is up to 98%due to typhoon in autumn and rainy season.（4）The annualΣ₁₆PAHs concentration in PM_2.5 in Shanghai ranged from 3.32 ng/m~3 to68.55ng/m~3,with an average of 12.39ng/m~3.The total concentration values of 7 kinds of PAHs with definite carcinogenicity ranged from 0.83 to 14.00 ng/m3,with an average of 3.7ng/m~3.Accounted for 13%-49%ofΣ₁₆PAHs,with an average of 27%.The concentration of the most carcinogenic Ba P monomer ranged from 0.06 to 1.21ng/m3,with an average of 0.35 ng/m~3.The total concentrations of 7 kinds of PAHs with definite carcinogenicity were winter>autumn>summer>spring.The concentration of carcinogenic PAHs increases rapidly in winter.（5）The result of molecular diagnostic ratios shows that PAHs in dry deposition of Shanghai is mainly the mixed source of incomplete combustion of coal,biomass and petroleum.There are obvious seasonal differences of sources in wet deposition.In dry season,PAHs mainly come from petroleum combustion and coal and biomass combustion,and in autumn rainy season,they come from coal and biomass combustion.coal and biomass combustion are main source type in spring and plum rainy season.PAHs in PM_2.5 are petroleum combustion and coal and biomass combustion mixed sources.（6）PMF model results show that the source types of PAHs in dry deposition of urban and suburban samples are consistent,including coking source,traffic emission source and oil leakage or volatilizing source.However,the contribution rates are different.The traffic emission sources occupy the dominant position in urban sample site,while in suburban site,the coking sources sample sites occupy the largest proportion.The wet deposition source types are oil leakage or volatilization,coal combustion,and gasoline and diesel sources in transportation emissions.The source types of PAHs in PM_2.5samples are complex.The simulation results of four seasons by using the HYSPLIT,PSCF and CWT model,the results show that the potential contribution areas of PM_2.5in Shanghai are mainly distant areas,and the contribution of other areas in the Yangtze River Delta is less.The contribution of exogenous transmission to Shanghai is similar in different seasons,but there are seasonal differences in regional spatial distribution.（7）The ILCRs model was used to evaluate the carcinogenic risk of people of different ages in different exposure ways.The results showed that the direct exposure of human skin to atmospheric particulate matter was the most carcinogenic risk.The carcinogenic risk of dry and wet deposition reached the maximum in dry season,and the ILCRs value of PM_2.5was winter>summer>autumn>spring.In addition,the cancer risk increases with age and the law of change is more obvious for women than men.