SAChE Atmospheric Dispersion (ELA967) Module 2 Practice Test

The main idea is to honor the ground as a boundary when modeling how concentration changes with height. In the vertical Gaussian distribution, the term with z minus H comes from the real plume source at height H above the ground. The term with z plus H comes from a mirror (image) source located at height −H below the ground. Adding these two contributions using the method of images effectively models the ground’s influence on the plume by reflecting it across the surface. This reflection changes how concentrations near the ground behave and helps reproduce the near-ground concentration pattern without having to solve a more complex boundary-layer problem. It’s not about deposition, chemistry, or wind shear; it’s about capturing the ground boundary’s effect through reflection.