Neutrally buoyant dispersion models

The models used to estimate the concentrations downwind of a release in which the gas is mixed with fresh air to the point that the resulting mixture is neutrally buoyant (Thus these models apply to gases at low concentrations, typically in the parts per million ranges.)
Reference: Chemical Process Safety – Fundamentals with Applications, 2nd Ed., Daniel A. Crowl/Joseph F. Louvar
Science/Dispersion Analysis/Dispersion Models