Abstract
In urban roads, vehicles continuously emitted gases and through  diffusion process, vehicle turbulence, heat flux and by  wind speed emission can transfer to upper stratosphere of  air and to road surroundings. There should be some pollutant that can not transfer instantaneously  because of inadequate wind velocity and for  road canyons. In due course, for certain time interval there should be some pollutant that could exist in the road surrounding.
 This paper pictures the formulation of a stochastic model of  this quantity of gas, and the concentration of expanded  gases in any particular area around the road  in any time period. More precisely, the paper deals with the effects of street canyon on the dispersion of pollutants from road environment. A mathematical model has been established to figure out the real situation of pollutants in urban roads. The model consists of traffic flow, emission and dispersion models, wind speed modeling near  road. The principal part of the model is to predict the total pollutant concentration near the ground which includes direct vehicle emissions, pollutants that can not be transferred before and  pollutants coming from surroundings. The prediction was performed using a bivariate normal probability density function. The variables are concentration of pollutants and wind speed. The pollutant that includes in this model is nitrogen oxides (NOx).