Hybrid Plume Dispersion Model (HPDM) Development and Evaluation

Abstract

The Hybrid Plume Dispersion Model (HPDM) was developed for application to tall stack plumes dispersing over nearly flat terrain. Emphasis is on convective and high-wind conditions. The meteorological component is based on observational and modeling studies of the planetary boundary layer. The dispersion estimates for the convective boundary layer (CBL) were developed from laboratory experiments and field studies and incorporate convective scaling, i.e., the convective velocity scale, w*, and the CBL height, h, which are the relevant velocity and length scales of the turbulence. The model has a separate component to handle the dispersion of highly buoyant plumes that remain near the top of the CBL and resist downward mixing. For convective conditions, the vertical concentration distribution is non-Gaussian, but for neutral and stable conditions it is assumed to be Gaussian. The HPDM performance is assessed with extensive ground-level concentration measurements around the Kincaid, Illinois, and Bull Run, Tennessee, power plants. It was also tested with limited data during high-wind conditions at five other power plants. The model is found to be an improvement over the standard regulatory model, MPTER, during light-wind convective conditions and high-wind neutral conditions.