Characteristics Of Polycyclic Aromatic Hydrocarbons (PAHs) In Dustfall In Urban Area Of Changping District,Beijing

Dustfall is an important fraction of atmospheric particulate,carrying many kinds of toxic and hazardous pollutants.It not only reduces solar radiation and visibility,but also takes air pollutants into other environmental media and thus plays an important role in the material exchange between the atmosphere and the earth surface.Polycyclic aromatic hydrocarbons?PAHs?,mainly derived from the combustion of fossil fuels and biomass,are persistent organic pollutants?POPs?and suspected human carcinogens existing in dustfall.Therefore,it is needed to investigate pollution status and major sources of PAHs in dustfall,which would help effectively control PAHs pollution and protect public health.In this study,gas chromatography/mass spectrometry?GC/MS?was used to measure 16 priority PAHs listed by United States Environmental Protection Agency?called“16 PAHs”below?in dustfall in Changping District,Beijing.The concentration,composition and deposition flux of PAHs in dustfall and their seasonal variation were discussed.The source of PAHs is apportioned using diagnostic ratios and principal component analysis?PCA?.The health risk resulting from dermal exposure of PAHs in dustfall were estimated using the toxicity equivalent quantity?TEQ?and incremental lifetime cancer risks?ILCRs?model.The main results are summarized as follows:?1?The total concentrations of 16 PAHs in dustfall in Changping District ranged from 2.22?g/g to 35.87?g/g.The carcinogenic PAHs accounted for 11.53%⁴7.51%.The PAHs composition was characterized by enrichment of PAHs containing less benzene rings.The total concentrations of 16 PAHs in dustfall varied significantly with seasons.The concentrations were highest in winter?4.85³5.78?g/g?,lowest in spring?2.22³.26?g/g?,and in middle in summer and autumn.The concentrations of PAHs in winter were higher than those in other seasons because of heating emission,infavorable diffusion condition and low photochemical reaction rate.?2?The dry deposition flux of dustfall in the Changping District ranged from 17.23mg/?m²·d?to 1489 mg/?m²·d?.Its seasonal variation was featured by the rank as spring?887.9 mg/?m²·d??>winter?327.8 mg/?m²·d??>autumn?238.3 mg/?m²·d??>summer?180.9 mg/?m²·d??.Frequent occurrence of dust storm is responsible for the high deposition flux in spring.The dry deposition fluxes of 16 PAHs and carcinogenic PAHs in Changping District were 0.94⁶.92?g/?m²·d?and 0.21².19?g/?m²·d?,respectively.The dry deposition fluxes of PAHs in four seasons were ranked as winter?4.70?g/?m²·d??>spring?2.57?g/?m²·d??>summer?1.78?g/?m²·d??>autumn?1.66?g/?m²·d??.Based on the measurments,about 1,385 kg of PAHs transferred to the ground by dry deposition in Changping District each year.?3?The diagnostics ratios and principal component analysis suggested that the main sources of PAHs in dustfall in Changping District were the combustion of coal and biomass.The great effects of vehicle exhaust and petroleum pollution were observed in certain periods.The contribution of coal combustion was 57.9%,followed by the sources of petroleum pollution and coke oven contributing 13.5%,and the contribution of traffic sources was 12.2%.?4?The TEQ of 16 PAHs in dustfall in Changping District ranged from 0.27?g/g to 10.44?g/g.The significant seasonality was observed for TEQ:the highest in summer?3.41?g/g?,moderate in winter?1.94?g/g?and in autumn?1.77?g/g?,and the lowest in spring?0.57?g/g?.The lifetime daily exposure dose of PAHs in dustfall in Changping District via skin exposure was 3.35×10^-77 mg/?kg·d?,and the resulted lifetime risk of cancer was 4.89×10^-6,which was within an acceptable level.