Analysis and modeling of urban dispersion experiments in neutral and stable atmospheres

Results of analysis of dispersion experiments conducted in Oklahoma City, Salt Lake City, London and St. Louis are discussed. We also present results of lab experiments of dispersion in model urban canopies undertaken in a water tunnel. A model to describe both sets of results is developed: the model is based on a simple Gaussian formulation where the diffusion coefficients are determined by the theories of Taylor (1921) and Hunt and Weber (1979). The data were analyzed and scaled by the appropriate variables. For both neutral and stratified conditions the data collapse well and support the predicted existence of near- and far-field dispersion regimes. The results suggest that dispersion in the urban environment is governed by the characteristic length scales of atmospheric boundary layer turbulence. Urban canopy length scales are likely to dominate dispersion only at short distances (approximately 50m) from the source.