NUMERICAL SIMULATION FOR THE EFFECTS OF PBL AND THE SURFACE ON POLLUTANT CONCENTRATIONS

On the basis of theoretical and experimental results of study of planetary boundary layer (PBL), the physical parameters describing the structure of PBL are calculated by using the data obtained from a meteorological tower and the effects of PBL and the surface on pollutant concentrations are numerically simulated with a time-dependent two-dimensional advection and diffusion equation.It is shown that the diurnal variation of PBL results in that of concentration. The height of mixing layer is an important factor to determine the ground-level concentration. As for an elevated point source, the height of mixing layer, growing from lower to higher than the releasing height is a necessary condition for the phenomenon of fumigation. It is also shown that the surface may be considered as a boundary with perfect reflection when Vd ≤0.001 m s-1, but has an important effect on concentration and must be carefully dealt with when Vd≥0.01 m s-1.