ISCST3 Tech Guide

Gaussian Plume Air Dispersion Model

6.5.5 The Dispersion Parameters

The dispersion parameters used in the complex terrain algorithms of ISC are the same as the point source dispersion parameters for the simple terrain algorithms described in Section 1.1.5.1, except that the radial distance is used instead of the downwind distance. Since the lateral distribution of the plume in complex terrain is determined by the sector average approach, the complex terrain algorithm does not use the lateral dispersion parameter, Fy. The procedure to account for buoyancy-induced dispersion in the complex terrain algorithm only affects the vertical dispersion term (see Equation 1-48). Since the complex terrain algorithm does not incorporate the effects of building downwash, the enhanced dispersion parameters and virtual distances do not apply.