Gaussian Plume Model — EPA SCREEN3 Methodology
Enter 0 to calculate maximum ground-level concentration and its distance
Understand Gaussian dispersion, stability classes, Briggs plume rise, and EPA modeling guidance
The Gaussian plume model is the standard EPA methodology for estimating ground-level pollutant concentrations from elevated point sources (stacks). It assumes the plume spreads in a Gaussian (bell-curve) distribution both laterally and vertically as it travels downwind, with dispersion rates determined by atmospheric stability class (A through F) and distance.
Effective stack height equals the physical stack height plus plume rise. Plume rise is calculated using Briggs equations accounting for buoyancy (hot exhaust gas rising due to temperature difference) and momentum (exit velocity). For most industrial sources, buoyancy dominates. Effective heights are typically 1.5 to 3 times the physical stack height.
Good Engineering Practice (GEP) stack height per 40 CFR 51.100 is H + 1.5L, where H is building height and L is the lesser of building height or projected width. If a stack is shorter than GEP height, building wake effects can bring the plume down to ground level (downwash), significantly increasing ground-level concentrations near the source.
For worst-case screening analysis, use Stability Class F (very stable) with low wind speed (1-2 m/s) for rural sites, or Class D (neutral) for urban sites. Class A (very unstable) gives the highest short-distance concentrations. EPA SCREEN3 methodology tests all stability classes and reports the maximum concentration.