ISCST3 Tech Guide

Gaussian Plume Air Dispersion Model

7.1.6 The Vertical Term

The Vertical Term for Gases and Small Particulates.

Except for the use of seasons and discrete categories of wind-speed and stability, the Vertical Term for gases and small particulates corresponds to the short term version discussed in Section 1.1.6. The user may assign a separate mixing height zi to each combination of wind-speed and stability category for each season.

As with the Short-Term model, the Vertical Term is changed to the form:


at downwind distances where the Fz/zi ratio is greater than or equal to 1.6. Additionally, the ground-level concentration is set equal to zero if the effective stack height he exceeds the mixing height zi. As explained in Section, the ISC model currently assumes unlimited mixing for the E and F stability categories.

The Vertical Term in Elevated Terrain.

See the discussion given in Section

The Vertical Term for Large Particulates.

Section discusses the differences in the dispersion of large particulates and the dispersion of gases and small particulates and provides the guidance on the use of this option. The Vertical Term for large particulates is given by Equation (1-53).