AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

6.5 Plume Rise Calculations in AERMOD

For the direct source, hd is taken from (Briggs, 1984) as:

Equation (116)
Equation (117)

It should be noted that uP is the wind speed used for calculating plume rise. In the CBL uP is set equal to u{hs}. While in the SBL uP is initially set equal to u{hs} but its final value is determined by iterating.

The indirect source, which we include to treat the no flux condition at z = zi , uses a modified reflection approach in which the reflected vertical velocity is adjusted by the addition of a plume rise term h , designed to keep the plume aloft (Weil et al., 1997), such that

Equation (118)

The height that the penetrated source achieves above zi is calculated as the equilibrium plume rise in a stratified environment and is determined by the source buoyancy flux, the stable stratification above zi , and the mean wind speed. In line with Weil et al. (1997), we assume that the plume I height h is the centroid of the plume material above the inversion and take hep = hs+ heq for fP = 0 or complete penetration. However, for partial penetration ( fP > 0), hep is chosen as the average of the heights of the upper plume edge hs + 1.5heq and zi , or

Equation (119)

where heq is defined in eq. (68).