Dispersion of a Passive Flare over a City: A Numerical Experiment

摘要

A technique for calculating the effect of urban roughness on the flow of air and propagation of contaminants in meso-scale atmospheric models is presented. The influence of the urban roughness is not resolved apparently, though its influence on the wind field and temperature is parameterized. The parameterization is constructed in an improved meso-scale model and is tested in the two-dimensional case for a city on a planar surface. In a Euler diffusion model turbulent flows of a concentration of contaminants are calculated from fully explicit algebraic expressions. These are obtained by simplification of the transport equations for turbulent flows in an approximation of weakly equilibrium turbulence with the use of symbolic algebra. Numerical calculations of the dispersion of the contaminant show that the mechanical (urban roughness) and thermal (urban heat island) factors exert a substantial influence on the dispersion of contaminants over an urbanized surface and that the city also produces effects on the daytime concentration of contaminants over the city.