Simulations of the ozone formation caused by traffic in urban areas

Abstract

A box model and a vertical cell model for simulations of the ozone formation caused by traffic in urban areas are presented. Diurnal variations of emission rates are calculated on the basis of assumed diurnal traffic cycles. In both models the critical case of vanishing horizontal advective transport is considered. In the vertical cell model turbulent diffusion is described using suitable parameterizations for the eddy diffusivity and the mixing layer depth. Photochemical smog formation is modeled using alternatively a compact and a detailed reaction mechanism. The compact mechanism of Eschenroeder and Martinez (EM mechanism, Adv. Chem. 113, 101–167, 1972) can be regarded as an adequate basis for a qualitative description of photochemical transformations in the case that no detailed data on hydrocarbon emissions are available. Predictions of the O 3 formation using this mechanism are fairly similar to corresponding predictions achieved with the detailed reaction mechanism of Atkinson, Lloyd and Winges (ALW mechanism, Atmospheric Environment 16, 1341–1355, 1982). Hence, if the ALW mechanism is valid, the EM mechanism may be used to obtain a reasonable impression of the diurnal variation of the O 3 formation in an urban airshed. The simulation results illustrate the effects of traffic density and vertical turbulent diffusion on the O 3 formation in such an airshed.