VOC speciation of vehicle emissions: what is the impact on air quality modelling?
by Anne Jaecker-Voirol, Bernard Jouve, Philippe Quandatle, Julien Salles
International Journal of Vehicle Design (IJVD), Vol. 20, No. 1/2/3/4, 1998

Abstract: A numerical model named AZUR has been developed by IFP-EDFLISA to simulate regional episodes of photochemical pollution. This model requires data on pollutant emissions defined at space and time scales corresponding to one square kilometre and one hour. In addition to the amount of emitted pollutants, the knowledge of their chemical composition is of prime interest for correctly representing air chemistry through detailed modules such as MOCA. It is therefore important to know the emitter type in order to assign an appropriate chemical composition to various pollutant flows. IFP has developed a set of methods whose aim is to determine an inventory of traffic-related pollutants (CO, SO₂, particles, VOCs and NO_x). They are based on the knowledge of the vehicle density and average traffic flow at the site of each measurement point. Density and speed data were converted into pollutant flows using emission factors (in grams of pollution per km travelled) as functions of speed. The emission factors are specific to each vehicle category. Separate counts for each category enabled us to assign, as previously mentioned, a specific chemical composition (in particular for VOCs) to emissions in each category. But very few data are available regarding the VOC emission speciation as a function of different vehicle types. Moreover, these data are very often associated with a specific driving cycle, which does not necessarily correspond to cycles used for determining emission factors. The purpose of this paper is to evaluate the impact of these uncertainties in VOC speciation. Air quality in the Paris area will be simulated using the AZUR model with various VOC distributions. These distributions, taken from the literature, are either measurements carried out using specific driving cycles or overall values. Ozone profiles will be analysed and compared in both urban and rural areas to assess the sensitivity of results to the VOC distribution related to road traffic.

Online publication date: Mon, 18-Aug-2003

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