In the present study a numerical model is used for dispersion simulation of vehicle emissions when investigating air quality in street canyons.In a first approach,the two-dimensional street canyon model with the same height for both sides of buildings is adopted when the inflow wind is perpendicular to the street canyon.A second set of calculations using a three-dimensional simulation model of the street canyon with the same inflow wind and geometry as in the two-dimensional street canyon model is performed to investigate the wind flow field and concentration distribution within the street canyon.Comparing the resulting data from the two different models,discrepancies between both models are found for the prediction concentration fields in the street canyon when simulating car exhaust dispersion.