Urban dispersion - challenges for fast response modeling

Transport and diffusion of an airborne contaminant within a city is extremely complicated. Complex wind patterns develop as a function of building height variation, shapes, spacings, and relative layout. There are a number of groups involved in computational fluid dynamics modeling of city centers, but for many applications (e.g., emergency response, training, vulnerability assessments) a fast response model is required. To reasonably account for the effects of clusters of buildings on the flow fields in a simplified, non-full-physics model is extraordinarily challenging. In this presentation, we will illustrate some of the complexities of plume dispersion in cities, why accounting for urban effects is important, present a brief overview of urban fast response models, and through examples of model output illustrate pitfalls and successes of these models.