Volatile Organic Compound Emissions from Light-Duty Vehicles During Cold-Starts

Abstract

Cold-starts have been catalogued as one of the periods during the operation cycle of vehicles where significant amounts of volatile organic compound (VOC) emissions can occur. In this work we present the results of two monitoring campaigns held in the Metropolitan Area of Monterrey, Mexico, where the exhaust gases of 20 re cent-model ligh-duty vehicles were characterized during cold-start events. The collected samples were chemically analysed to obtain the corresponding VOC emission profiles. The chemical analysis focused on 30 alkanes and aromatic species in the range C5 to C9. The results revealed that the species with high estconcentrations were Dimethylhexane, 2,2,4-Trimethylpentane, and 2,3,4-Trimethylpentane. More over, it was found that vehicles that used the same type of gas o line (Magna or Premium) tended to have a similar chemical profile of their emissions, and statistically different from the other group. The effect of milage, model-year or brand of the vehicle did not affect this result. This implies that the chemical profile of the emissions during cold-starts is practically an exclusive function of the type of gas o line used, and not of the vehicle's conditions. Averageratios between Benzene, Toluene, and Ethylbenzene emissions were also calculated (T:B - 1.9, E:B - 0.6 y B:T - 1.5), and were in the reference ranges found in the literature. Finally, the emitted species were classified according to their reactivity (ozone forming potential) using apropylene-equivalent concentration scale. It was found that the reactivity of the exhaust gases is governed by the first and third most abundant identified species (Dimethylhexane and 2,3,4-Trimethylpentane). The rest of the species do not necessarily have the same position in the concentration scale as in the reactivity scale.