Method development, speciated measurements and culculated reactivities of benzine, toluene, ethylbenzene and xylenes from vehicle exhaust

Mathematical modeling of ambient air photochemistry requires comprehensive speciation of hydrocarbons from mobile source emission. The objective of this study is to develop a simple and reliable method for analyzing tailpipe emission focusing on benzene, toluene, ethylbenzene and xylenes (BTEX). The method consists of sampling, qualitative analysis and quantitative analysis. The samples were collected in Tedlar bags at cold start and hot start conditions and were injected manually using a gas-tight syringe into Gas Chromatograph-Mass Spectrometer (GC-MS) operated on Electron Impact Ionization (EI) mode. The method developed has demonstrated ability to produce rapid and reliable separations of exhaust hydrocarbons. An approximate of 50 hydrocarbon compounds were identified in the exhaust ranging from C₄ to C₁₂. It was found difficult to analyze C₁ to some of the C₄ hydrocarbons without the required accessories for volatile organic gases analysis. The emission rate of BTEX was emphasized because of its potential carcinogenicity and toxicity. High concentration of BTEX was observed during cold start and hot start. The mean concentrations of BTEX at cold start were as follows: benzene (55.4 ppm), toluene (184.7 ppm), ethylbenzene (50.2 ppm), m-xylene (143.9 ppm), p-xylene (59.0 ppm) and o-xylene (65.4 ppm). The mean concentrations ofBTEX at hot start were as follows: benzene (82.4 ppm), toluene (198.3 ppm), ethylbenzene (40.0 ppm), m-xylene (184.0 ppm), p-xylene (62.1 ppm) and o-xylene (50.3 ppm). The concentrations of BTEX in weighted percentages for all cars were fairly constant. The weighted percentages concentration was used to estimate the photochemical ozone reactivity by applying the Maximum Incremental Reactivity (MIR) factors to the concentrations. The ozone forming potential as a result ofBTEX emission from vehicle exhaust were estimated as follows: 3.07 g O₃/g benzene, 74.64 g O₃/g toluene, 13.0 g 0₃/ g ethylbenzene, 145.8 g O₃/g m- and p-xylene, and 50.97 g O₃/g 0- xylene. The results suggested that BTEX emitted from the vehicle exhaust increases the formation of photochemical ozone in the atmosphere significantly.

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