An unsteady two-dimensional transport model is constructed to study the short-term effects of urbanization and air pollution on the thermal structure and dispersion in an urban atmosphere. The model includes horizontal and vertical advection as well as turbulent diffusion and radiative transfer in the planetary boundary layer (PBL). The gaseous and particulate pollutants as well as the natural constituents in the atmosphere absorb, emit, and anisotropically scatter radiation. The variation of the physical properties of the soil, the radiation characteristics of the earth’s surface, and the urban heat and pollutant emissions along the city are modeled. A number of numerical simulations for summer conditions modeling a typical Midwestern city are performed and the effects of various parameters arising in the problem have been investigated. The diurnal variation of the temperature structure and pollutant concentrations are discussed. It was found that the temperature changes caused by radiatively participating pollutants are generally smaller than the effects induced by urbanization. A maximum urban heat island of approximately 3°C was predicted and found to be in good agreement with observations.

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