Close Menu


A model is a mathematical estimation of pollutant concentrations in selected locations near one or more pollutant sources and/or selected areas located downwind from a source or sources. An air dispersion model simulates how air pollutants emitted by a source will disperse and react in the atmosphere to affect ambient air quality. Modeling is conducted utilizing specialized computer programs. Results are obtained using inputs including emissions data, stack information and meteorological data.

Air quality modeling data is utilized for air permitting and National Ambient Air Quality Standards (NAAQS) implementation. The Indiana Department of Environmental Management's Office of Air Quality (IDEM OAQ) requires air dispersion modeling to be conducted to demonstrate that a source will not cause or significantly contribute to the violation of air quality standards. Modeling also must comply with the Prevention of Significant Deterioration (PSD) increments (allowable increases that prevent the air quality in clean areas from deteriorating to the level set by the NAAQS) or toxic thresholds. IDEM follows all air quality modeling procedures set forth in the U.S. Environmental Protection Agency (U.S. EPA) Guideline on Air Quality Models for PSD, nonattainment New Source Review (NSR), and State Implementation Plan (SIP) revisions