The main part of the atmospheric boundary layer is the mixed layer, in which air pollution is uniformly dispersed. In this work, the mechanisms involved in the growth of the mixed layer is first discussed and a turbulence model is presented for its growth. The results of this model is used in an integral model for air pollution prediction in an urban area. Using a correct model with proper adjustments, one can predict the air pollution concentration for various urban areas with different conditions, with some accuracy. From the comparison of-the results, with actual measurements, obtained for two typical summer and winter days, it is clear that the model can correctly predict the daily variation of pollution concentrations. Typical winter concentrations are higher than for the summer ones. For cities like Tehran, topography and air stability, can limit the air flow, and hence, can cause substantial increase in air pollution concentrations