An Updated Gaussian Plume Model for Tall Stacks

Abstract

This paper describes and evaluates a Gaussian plume model, PPSP, which Incorporates stability and dispersion parameters and plume rise formulas based on contemporary understanding of the planetary boundary layer. The model improvements over older Gaussian models such as CRSTER focus on daytime convective conditions, which Is when tall stacks usually yield their highest ground level concentrations. A major model advancement is the use of u/w* as the stability parameter during daytime rather than the Turner criteria. Here, u is the mean wind speed in the boundary layer, and w* is the convective velocity scale, which depends on the cube root of the surface heat flux and boundary layer depth. Other model Improvements include: 1) incorporation of Briggs’ dispersion parameters for elevated sources Instead of the Pasquill-Gifford curves for ground sources, 2) use of Briggs’ 1975 plume rise formulas, which address convectively generated turbulence, rather than his pre-1975 formulas, which do not, and 3) adoption of Briggs’ 1980 criteria for plume penetration of elevated stable layers instead of the simple "all or none" approach of the CRSTER model. Evaluation of the PPSP model with an extensive set of ground level SO2 measurements downwind of power plant stacks shows that it performs much better than the CRSTER model.