| With China's sustained,stable and rapid economic development,people's living standards have been greatly improved,and urbanization has also been rapidly developed.But at the same time,with the rapid development of economy,the urban air pollution is increasing,which has brought a serious of harm to people's health.Volatile organic compound(VOCs)is a kind of pollutants in air.Because of its toxicity and as it is an important precursor of ozone and secondary organic aerosol,volatile organic compound(VOCs)have been widely studied by scholars both at home and abroad.BTEX are important components of volatile organic compounds,which have been get a high degree of attention because of its environmental effects and the harm to the human body.With the continuous growth of urban car ownership,BTEX emissions from traffic sources are increasing,and the environmental pollution of the main road is becoming more and more serious.The monitoring of ambient air in two typical traffic arteries in Xi'an was carried out by activated charcoal adsorption carbon disulfide desorption coupled with gas chromatography.The levels,component characteristics,seasonal and diiurnal variations,chemical reactivity and health risk assessment of BTEX were studied.The results showed that the mass concentrations of BTEX were 42.30,31.80?g·m-3 in ambient air around Daqing and Chang'an road,respectively.The mass concentrations of benzene,toluene,ethylbenzene,o-m-and p-xylene in ambient air around Daqing road were 11.05?12.28?6.04?9.05?3.89?g·m-3,respectively,and those were 10.40?8.31?4.12?5.85?3.13?g·m-3 in ambient air around Chang'an road,respectively.Motor vehicle exhaust emission and fossil fuel combustion emissions were the two main resources of pollution in the study area.The total concentrations of BTEX in ambient air of Daqing road and Chang'an road were changed to winter,autumn,spring and summer.The concentrations of BTEX were the highest in winter and then in autumn and spring,and the lowest in summer.It was related to meteorological conditions,photochemical reactions and emission of pollution sources.Diurnal variation characteristics showed that the concentrations of BTEX in Daqing road in winter,spring and autumn were all relatively high in the early,middle and late of a day,which was related to the peak traffic emissions and the fuel consumption of the catering industry.In summer,the concentrations were higher in the morning and evening while lower in the afternoon.The reason was that the concentrations of BTEX in ambient air were reduced effectively by the rapid photochemical reaction and the convection diffusion.The diurnal variation characteristics of BTEX in Chang'an road in autumn and winter were"W"(three peaks)type,and the peak value of spring and summer was in the morning and evening.The change trend of BTEX concentrations in the ambient air of Chang'an road was different from that of Daqing road after 6 p.m.Chang'an road was on the rise while Daqing road is on the decline,which was related to meteorological factors and people's living habits.The study of chemical reactivity showed that the OH radical loss rate of m-,p-xylene was the highest and benzene was the lowest.The m-p-xylene in ambient air had the highest OFP.The SOA formation potential of BTEX in ambient air were changed to winter,autumn,spring and summer.The SOA formation potential of toluene and m-p-xylene were the highest in different seasons.The study of human health risk assessment showed that the risk of non-carcinogenic hazard index was 2.53E-01,2.21E-01 in ambient air around Daqing and Chang'an road,respectively.BTEX in ambient air had no risk of non-cancer health effect on the exposed population in study areas.The cancer risk of benzene was 4.31E-05,4.06E-05 in ambient air around Daqing and Chang,an road,respectively.It indicated that benzene had potential cancer risk to the exposed population in study areas. |
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