Terms and Definitions

Potential to Emit:

How is it determined whether a source needs a permit, and if so, what type?

The appropriate level of permitting required by any emission source is based primarily on its potential to emit. The potential to emit (See 326 IAC 2-1.1-1(16)) is the total potential emissions of any regulated pollutant which could result from operating under a "worst case operating scenario," running twenty four hours a day (with no pollution control equipment), 365 days a year at full capacity. Once a source's potential to emit has been determined it can be used to determine the level of permitting required, and the permitting process can move forward. The IDEM construction permit application includes a form where applicants can calculate the potential to emit or the IDEM staff will perform the calculations for any properly completed air registration or permit application.

What are the Regulated Air Pollutants?

The federal standards first set forth in the Clean Air Act (CAA) of 1970 are the basis upon which Indiana has established emission thresholds and regulations for what are now known as the regulated pollutants. The 1970 CAA identified the criteria pollutants, established the first of an ongoing series of New Source Performance Standards (NSPS), and set the National Emissions Standards for Hazardous Air Pollutants (NESHAP). The same pollutant may be regulated under more than one of these three regulatory standards. For example, particulate matter is both a criteria pollutant and is regulated under NSPS for certain types of sources while lead is both a criteria pollutant and is regulated under NESHAP.

The Criteria Pollutants are those for which National Ambient Air Quality Standards have been established, and their precursors. The Criteria Pollutants, which are used to calculate whether a geographical area (county or urban area) is in "attainment" or "non-attainment" with the standards of the Clean Air Act, are:

  • Ozone (low level or at ground level)
  • Nitrogen dioxide (NO2) and oxides of nitrogen (NOx)
  • Carbon monoxide (CO)
  • Sulfur dioxide (SO2)
  • Particulate matter; fine particulate matter (PM2.5) and coarse particulate matter (PM10)
  • Lead (Including both lead and lead compounds)