This report describes the development of techniques for modeling the microscale phenomena associated with urban air pollution. Such phenomena include turbulent diffusion, turbulent concentration fluctuations, and sub-grid scale variations in the time averaged concentration field. Optimal eddy diffusivities were reexamined to determine whether (1) the diffusivities are unique, (2) they have a universal form when properly scaled, and (3) they are dependent on source height. A model for describing the effects of turbulent concentration fluctuations on second-order chemical reactions has also been developed and tested. It was applied to the case of NO emanating from a point source into an O3 laden atmosphere. Results showed that the rate of conversion of NO to NO2 is greatly inhibited by turbulent concentration fluctuations, even under stable conditions. A method of paramaterizing the effects of chemical reaction rates of both subgrid-scale concentration variations arising from ground-level sources and turbulence-induced concentration fluctuations has also been developed. In addition, theoretical frameworks for two models of pollutant levels around roadways are introduced.