The properties of the atmospheric boundary layer (the layer closest to the surface) are much more difficult to describe in urban areas than in most rural areas because the buildings present obstacles that are variable, hard to characterize statistically, and large enough to extend a significant distance into the boundary layer. Prediction of how a release of a hazardous material will disperse in an urban setting, for example, relies on accurate characterization of turbulent fluctuations in the air motions, and such characterization is particularly difficult within cities. Several recent comprehensive experiments have collected measurements with which to characterize the urban boundary layer, but those measurements have not been analyzed comprehensively or as an ensemble. This project will use a set of models and those existing data sets to develop generalized characteristics of turbulence in the urban boundary layer, and it will examine how those characteristics relate to those of the boundary layer in unobstructed rural areas. The results will be used to develop ways of representing or parameterizing the effects of the urban surface on the urban boundary layer, and those parameterizations will be incorporated into dispersion models. The improved and tested models will then be able to provide tested predictions of dispersion in urban areas. The expected result is improved ability to predict how hazardous releases or other sources of urban pollution will affect the populations of cities.
