Air quality simulation models applied at various horizontal scales require different degrees of treatment in the specification of the underlying surfaces. As we model neighborhood scales (approx. 1 km horizontal grid spacing), the representation of urban morphological structures (e.g., building and area distributions, and compositional materials for impervious structures such as roads and parking areas) requires much greater detail. At the neighborhood scale, we expect that the heterogeneities of structures within the urban canopy (i.e., the layer between the surface and the tops of the buildings) will exert a strong influence on the urban boundary layer (UBL) wind and thermodynamic structure and a subsequent effect on the pollutant dispersion and resulting air quality predictions.