TURBULENT DISPERSION OF POLLUTANT OVER COMPLEX TERRAIN

A two-dimensional turbulent diffusion equation is derived in a streaml ine coordinate system, defined for rotational flow over complex terrai n and limited aloft by an elevated, impenetrable inversion. In the fir st instance, the steady-state equation is solved for an ''inner region '' of the boundary layer, in which the effect of curvature is negligib le and, for simplicity, it is assumed that vorticity has a power-law d ependence upon stream function. A variational method of solution is al so discussed, in which vorticity may have a more general representatio n. A numerical calculation is performed for a special case of symmetri cal flow over an isolated hill. The dependence of pollutant concentrat ion upon the flow field, downwind distance and source is examined and the effect of wind acceleration in the neighbourhood of the top of the hill is discussed It is pointed out that the diffusion model can be a pplied to any realistic flow field, provided that the streamlines are specified.