One of the many “regulatory activities” associated with the permitting process involves the computer simulation of air pollutant emissions from a source to predict air pollution concentrations and dispersion in the area downwind from the source’s location.

National Ambient Air Quality Standards (NAAQS) are established by USEPA for the criteria pollutants and recognized by state and local air quality agencies as the maximum air pollutant concentrations which can be measured or predicted in a community before the community is designated a Non-Attainment Area (NAA).

This process is often referred to as dispersion modeling or permit modeling, and predicted concentrations are usually referred to as “ambient impacts” (pollutant concentrations in the area surrounding the facility where the source is located). Pre-construction permitting under the Clean Air Act often requires air dispersion models to estimate the air quality impact from proposed new and modified sources.