Characteristics And Risk Assessment Of PAHs In Dry And Wet Sediment Of Taiyuan City

Dry and wet depositions were the main ways for pollutants removing from the atomosphere. In this study, dry and wet deposition samples were collected from August 2013 to October 2014 in Taiyuan, and 16 priority PAHs were analyzed in the laboratory. We firstly reported the concentration levels, compositions and distribution of 16 priority PAHs in the dry and wet deposition, then discussed its eclogical risks and emission sources, and finally estimated the dry and wet deposition fluxes of PAHs in Taiyuan. The results could provide basic information for understanding the PAHs removement and environmental geochemical effects in dry and wet deposition in Taiyuan. The main conclusions were as followed:(1) PAHs levels in the dry deposition samples were in the range of 19.61~61.91 μg/g, with the mean level of 32.42 μg/g. The PAHs ring distribution were 54.56% for 2~3 rings, 29.12% for 4 rings and 16.32% for 5~6 rings, respectively.(2) PAHs levels were in the range of 965.97~44393.80 ng/L in the water and particulate phase of rainfall, was and distributed 350.90~10704.0 ng/L in the water phase and 332.45~35532.68 ng/L in the particulate phase. The PAHs in the particulate phase was accounted for 67.28% in total PAHs. The percents of 2~3 rings PAHs for total PAHs, water phase PAHs, particulate phase PAHs were 67.56%, 70.97% and 65.54%, respectively.(3) The PAHs fluxes in Taiyuan were 6560.90~16289.60 ng/(m2·d) for the total dry and wet deposition,4196.4~14769.8 ng/(m2·d) in the dry deposition, 319.98~10608.00 ng/(m2·d) in the wet deposition. Atmosphereric dry deposition was the main method for PAHs removing from the atmosphere in Taiyuan. Accordingly, 16 priority PAHs removed from the atmosphere by dry and wet deposition was 31.57 t in Taiyuan in 2013, including 23.90 t by dry deposition and 7.67 t by wet deposition.(4) The toxic equivalent concentrations(TEQ) of BaP in dry deposition and rainwater were in the range of 0.86~2.80 μg/g and 26.94~2456.28 ng/L, respectively. It was worth noting that the TEQ for all rainwater samples were higher than the limit value of the environmental quality standard for surface water issused by the Ministry of Environmental Protection(MEP), People’s Republic of China and may pose a higher ecological hazard. By the ecological effect range method, PAHs from dry deposition may pose the medium or higher risk to the ecological system.(5) Diagnostic ratios results showed that PAHs in dry and wet deposition were mainly from coal burning and petroleum sources. Principal component analysis indicated that coal burning, vehicle exhaust and coking emission were three main soures of PAHs in dry deposition and rainfall in Taiyuan.