Simulation Of Urban-Scale Dispersion Using A Lagrangian Stochastic Dispersion Model

Based on recent knowledge concerning the vertical structure of turbulence statistics within the roughness sublayer (i.e., the layer directly influenced by individual roughness elements) over urban surfaces the problem of urban-scale dispersion is studied. On this scale it is impossible to resolve each roughness element so that the rough character of the surface has to be taken into account by introducing a roughness sublayer, which is generally not present in dispersion models even when employed in urban environments. Two types of simulations are presented here: one, called `urban’ takes into account the roughness sublayer's turbulence structure, while the other, `non-urban’ does not. A brief overview is given on what changes are required for an `urban' simulation as compared to a `non-urban' or standard dispersion simulation. In particular, a parameterisation is proposed for the vertical profile of Reynolds stress within the roughness sublayer.