Study On The Pollution Characteristics,Gas-particle Partitioning And Source Identification Of Polybrominated Diphenyl Ethers(PBDEs) And Polychlorinated Biphenyls(PCBs) In Atmosphere Of Urban Area Of Xi'an

“The Stockholm Convention”was signed to reduce and eliminate the emission of Persistent Organic Pollutants(POPs).China is one of the first contracting states and many Chinese researchers carried out various researches on POPs in the past decades.However,most of the POPs researches in China mainly focused on those developed regions such as the Yangtze River delta,the Pearl River delta and the Beijing-Tianjin-Hebei region.Xi'an is the central city for both the midwest area of China and Guanzhong urban and town agglomeration.There was limited studies focusing on POPs in this area and the basic data was scarce.Polybrominated diphenyl ethers(PBDEs)and Polychlorinated biphenyls(PCBs)are two typical kinds of POPs which had been used worldwide and they are very harmful to environment and human health.Although PBDEs and PCBs have been banned,they could still be found in the global atmospheric environment.Based on the situation mentioned above,a nearly six years monitoring campaign of PBDEs and PCBs in air was conducted in Xi'an.268 samples were collected,12 kinds of PBDEs and 80 kinds of PCBs were detected through the whole sampling period.In general,the concentration of?₁₁PBDEs(all PBDEs except BDE-209)and?_allPCBs both showed a trend of decline year by year,but the concentration of BDE-209 did not appear such obvious changes,indicating the possible existing of emission source of BDE-209.Comparing with other cities at home and abroad,the concentrations of PBDEs and PCBs in atmosphere in Xi'an were relatively low,but higher than that in background points.The result of health risk assessment showed that the risk of these two types of POPs to local children was relatively low,and the risk to adults was at a low or medium level.A close correlation was found between the concentration of PBDEs in the atmosphere and the local air temperature.However,there was no obvious correlation between the concentration of PCBs and air temperature.The concentration of PBDEs and PCBs were both affected by the concentration of TSP to some extent.The RP value of PBDEs,which showed the degree of deviation between the actual value and predicted value,was calculated by C-C equation.The three groups of sample data with Low RP,High RP and Middle RP were related to different meteorological factors and showed obvious distribution characteristics.Through the analysis of gas-particle partitioning of PBDEs and PCBs in the atmosphere in Xi'an,and it was found that the gas-particle partitioning did not reach the equilibrium state theoretically.The gas-particle partitioning parameters(log K_P)of these two types of POPs was further predicted by different gas-particle partitioning model,such as Dachs-Eisenreich model,Falconer-Harner model and Li-Ma-Yang model.The feasible conditions of each prediction model were obtained in the study.Through further analysis,it was revealed that meteorological factors,aerosol characteristics and"sampling interference effect"were important factors affecting the distribution of POPs,and the last factor was often overlooked.The source tracking system of POPs(for PBDEs and PCBs in the study)was established through the thorough investigation of three aspects:distribution of potential emission sources,source apportionment of pollutants and identification of potential source areas.It was found that:1)Most of the emission sources of PBDEs mainly located in southeast coastal areas and regions near the provincial capital cities while the emission sources of PCBs mainly located in Guanzhong urban and town agglomeration and the Yangtze River delta region.The results showed that the concentration distribution of PBDEs and PCBs in the atmosphere was close related with human activities and industrial production.2)It indicated that through principal component analysis(PCA)the pollution of PBDEs in the atmosphere of Xi'an city was mainly caused by the discharge of three commercial PBDEs,Penta BDE,Octa BDE and Deca BDE,while the pollution sources of PCBs was likely to be No.2 PCBs produced in China and No.1 PCBs transformer oil source produced in China.3)The"backward flow trajectory"model was applied to distinguish the contributions of local and foreign sources of PBDEs and PCBs.The potential source regions of PBDEs and PCBs gradually concentrated and shrank,and the source intensity gradually decreased,indicating that the atmospheric pollution of PBDEs and PCBs in the central and western regions of China was getting better.Overall,this thesis took urban areas of Xi'an as the research area,and the pollution levels,distribution and variation characteristics,health risk assessment of PBDEs and PCBs were analyzed respectively.A concept of classification of RP values was proposed,and a traceability analysis system of POPs was established.The variation pattern and pollution sources of PBDEs and PCBs in the atmosphere were investigated,which provided important essential data and method references for effective POPs monitoring and controlling in central and western China,and also made positive contributions to promoting sustainable economic and social development and building an environmentally friendly society in Shaanxi.