| Volatile organic compounds (VOCs) are one of the major gaseous pollutants in the atmosphere, components are complex and diverse, and even some of the compounds which are directly harmful to human health. VOCs are important precursors of the formation of photochemical oxidants. BTEX as a typical representative of VOCs, they are general term of benzene and derivatives. BTEX have wide source, high toxicity, more volatile, hardly degradable. In particular, benzene, that is highly caccinogenic, has become one of the EPA priority pollutants controlled substance. The pollution of BTEX is serious and complex in the atmosphere, especially traffic roads on both sides are the most polluted area. Most of BTEX with gaseous form through respiratory system and skin crowd into the exposure body and thus directly or indirectly threaten human health. Therefore, the measurement and analysis of BTEX has important theoretical and practical significance in environmental monitoring and protection of air.This paper was based on field sampling datas which are representative sample of Xi’an, detected and analysised these sampling datas with optimized gas chromatographic analysis methods. Based on monitoring datas of each the points to analysis BTEX distribution characteristics of space and time in urban air, findings the following areas:(1) The concentrations of BTEX in different functional areas under normal weather conditions was:Transportation District> Industrial Zone> Commercial district> Residential area> Scenic spot> cultural and educational areas, the average concentrations were:57.15μg/m3,36.02μg/m3,32.45μg/m3,23.15μg/m3,22.09μg/m3,14.35μg/m3. The compounds of BTEX form different functional areas roughly as follows:toluene> p-xylene between> benzene> ethylbenzene> o-xylene> styrene> cumene, the average percentage as follows:27.10%-34.33%,16.39%-23.62%,17.18%-21.60%,13.26%-23.41%,7.03%-11.30%,0%-5.64%,0-1.64%. The seasonal trends of BTEX were the concentrations of winter higher than the concentration of summer, but the seasonal variation of individual compounds had some differences. The seasonal changes are affected by the nature of the compound itself, meteorological conditions and emission sources, etc. The BTEX between each of the compounds exists significantly correlated, indicating that they have good homology. (2) Under normal weather conditions, the average concentration of BTEX of residential area at different locations—de Fu Xiang housing, Xi Da Xin Cun housing,west electronic community, Jin Dui Cheng housing was:30.45μg/m,24.15μg/m,18.26μg/m,9.29μg/m.wherein, the average concentrations of benzene, toluene, ethylbenzene, m-xylene, styrene, o-xylene, cumene were1.64-5.59μg/m3,3.39-8.06μg/m3,1.47-5.5μg/m3,1.86-6.08μg/m3,.0-0.78μg/m3,0.93-4.06μg/m3,0-0.76μg/m3. BTEX of this four residential areas rendered as:toluene> inter-xylene> benzene> ethylbenzene> o-xylene> styrene> cumene, the content percentage were:26.47%-36.49%,18.43%-29.68%,17.65%-20.38%,15.82%-18.10%,8.43%-13.33%,0%-2.98%,0-3.10%; The seasonal trends of BTEX was the concentrations of winter higher than the concentration of summer; The benzene and ethylbenzene has better homology of this four different residential areas, they mabey come from the same sources.(3) Under normal weather conditions, the average concentration of BTEX on the different types of traffic road were:Zhong Lou69.99μg/m3, Xi Da Xi Men59.14μg/m3, Dian Zi Shan Cheng45.44μg/m3, Guo Du29.97μg/m3. BTEX constitute ratio:toluene> Inter-xylene> benzene> ethylbenzene> o-xylene> styrene> cumene, the average percentage of were:31.98%,18.97%,16.66%,15.91%,11.04%,4.70%,0.73%. The main relevance of each compound with BTEX was B/T (benzene/toluene), it can be used to determine the initial source of BTEX, if B/T of about0.5, indicating BTEX mainly from motor vehicles exhaust emissions. The average B/T values of this different types of traffic road were closer to0.5, which infering vehicle exhaust is the primary source of BTEX pollution, and benzene and ethylbenzene show good homology, they likely to come from the same sources. BTEX diurnal variation was:the concentrations of peak higher than the concentration of flat peak, which was relevant to the traffic, atmospheric stability, and special inversion phenomenon. Overall seasonal variation BTEX concentrations in winter than in summer showing concentration, the average concentration of BTEX were summer for24.69-61.72μg/m3, winter for32.58-78.26μg/m3.(4) To some extent, weather conditions have some effects on the concentration of BTEX, rainfall is conducive to the removal of BTEX in air. The concentrations of BTEX of haze were significantly higher than the concentrations of sunny weather conditions, haze obviously devoted to pollutants accumulation. |
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