Air Dispersion Modeling Overview


As part of the air permitting process, facilities in South Carolina are required to demonstrate that the emissions coming from their sources will not cause the violation of any applicable South Carolina air pollution control regulations or standards. It is a required part of many air construction permits (including all Prevention of Significant Deterioration (PSD) construction permits) and some Title V, conditional major, and state operating permits and renewals.

Air dispersion modeling is typically used to demonstrate compliance. Your facility's location, emissions, and the quality of the local ambient air could require you to submit an air dispersion modeling analysis to demonstrate compliance with the National Ambient Air Standards (NAAQS) for criteria pollutants, the State Ambient Air Quality Standards as promulgated in Regulation 61-62.5 - Standard No. 2 (pdf), Regulation 61-62.5 - Standard No. 3.1 (pdf) , Regulation 61-62.5 - Standard No. 7 (pdf) , Regulation 61-62.5 - Standard No. 7.1 (pdf) , and/or Regulation 61-62.5 - Standard No. 8, Toxic Air Pollutants (pdf).

The South Carolina Air Quality Implementation Plan , sets limits on criteria pollutant emissions to ensure that air quality in the area is in attainment with the NAAQS. Air dispersion modeling analyses are performed to determine air quality impacts at your facility's property line and beyond. Certain counties have individual criteria pollutant baselines established because of emissions data for existing major source facilities located in the area. Any increases in emissions from a new or modified emission source must comply with the initial baselines set in that county. If your new facility is locating in a county with one or more criteria baselines, you will be required to submit air dispersion modeling data that demonstrates emissions increases caused by the facility will not cause an increase in pollutant concentration above the maximum allowable increase over the baseline concentration.

Who Needs to Use It?

An air dispersion model is a set of mathematical equations that relates the release of air pollutants from emission sources to the corresponding concentration of pollutants in the ambient air. These models are tools used to determine if the emissions from a source can meet a specific ambient air standard.

Regulations may allow other approaches, but air dispersion modeling is typically the least expensive and least time consuming approach.

The emission sources/facilities can use air dispersion modeling to show compliance with federal and/or state air pollution control laws and regulations, such as:

  • South Carolina Air Pollution Control Regulation 62.5:
  • Prevention of Significant Deterioration (PSD)
  • Construction permits
  • Title V
  • Conditional major
  • State operating permit renewals.