NNSR Permit Glossary: Key Terms & Definitions for Developers and Consultants

NNSR Permit Key Terms & Definitions

Actual Emissions: The measured or estimated emissions from a source or project, as opposed to its potential emissions. Actual emissions are used in various NSR applicability determinations and emission calculations.

Ambient Air: The portion of the atmosphere, external to buildings, to which the general public has access (40 C.F.R. § 50.1(e)). NSR permitting requirements are designed to protect ambient air quality.

Attainment Area: An area that meets the National Ambient Air Quality Standards (NAAQS) for a specific pollutant. NSR permitting requirements differ for attainment and nonattainment areas.

Best Available Control Technology (BACT): An emission limitation based on the maximum degree of reduction for each regulated pollutant, taking into account energy, environmental, and economic impacts. BACT is required for major sources in attainment areas under the Prevention of Significant Deterioration (PSD) program (40 C.F.R. § 52.21(b)(12)).

Emission Offset: A reduction in emissions from an existing source that compensates for emissions increases from a new or modified source in a nonattainment area. Emission offsets are required under the Nonattainment New Source Review (NNSR) program to ensure a net air quality benefit (42 U.S.C. § 7503(a)(1)(A)).

Fugitive Emissions: Emissions that could not reasonably pass through a stack, chimney, vent, or other functionally equivalent opening (40 C.F.R. § 70.2). Fugitive emissions are considered in NSR applicability determinations for certain source categories.

Lowest Achievable Emission Rate (LAER): The most stringent emission limitation achieved in practice or required by any State Implementation Plan (SIP) for a specific class or category of sources. LAER is required for major sources in nonattainment areas under the NNSR program (42 U.S.C. § 7501(3)).

Major Modification: A physical change or change in the method of operation that results in a significant net emissions increase of a regulated pollutant. Major modifications are subject to NSR permitting requirements (40 C.F.R. § 52.21(b)(2)).

Major Source: Definition #1: A source with the potential to emit 100 tons per year or more of any air pollutant, for source categories listed in 40 C.F.R. § 52.21(b)(1)(i)(a). Definition #2: A source with the potential to emit 250 tons per year or more of any air pollutant, for all other source categories (40 C.F.R. § 52.21(b)(1)(i)(b)).

National Ambient Air Quality Standards (NAAQS): Health-based standards for air pollutants established by the U.S. Environmental Protection Agency under the Clean Air Act. The NSR program helps ensure that new or modified sources do not cause or contribute to violations of the NAAQS (42 U.S.C. § 7409).

Nonattainment Area: An area that does not meet the NAAQS for a specific pollutant. NSR permitting requirements are more stringent for sources in nonattainment areas.

Nonattainment New Source Review (NNSR): The NSR permitting program for major sources in nonattainment areas, which requires the installation of LAER, the acquisition of emission offsets, and a demonstration that the benefits of the source outweigh its environmental and social costs (42 U.S.C. § 7503).

Plantwide Applicability Limitation (PAL): A voluntary emissions limitation established for an existing major source, which allows the source to make changes without triggering NSR permitting requirements as long as the PAL is not exceeded (40 C.F.R. § 52.21(aa)).

Potential to Emit (PTE): The maximum capacity of a source to emit a pollutant under its physical and operational design, taking into account enforceable limits on emissions (40 C.F.R. § 52.21(b)(4)). PTE is used to determine whether a source is subject to NSR permitting requirements.

Prevention of Significant Deterioration (PSD): The NSR permitting program for major sources in attainment areas, which requires the installation of BACT, an air quality analysis, and additional impact analyses (42 U.S.C. § 7470 et seq.).

Regulated NSR Pollutant: The pollutants for which NSR permitting requirements apply, including criteria pollutants (sulfur dioxide, nitrogen oxides, particulate matter, ozone, carbon monoxide, and lead) and certain non-criteria pollutants (40 C.F.R. § 52.21(b)(50)).

Significant Emissions Increase: An emissions increase that equals or exceeds the significance thresholds for a regulated NSR pollutant, triggering NSR permitting requirements (40 C.F.R. § 52.21(b)(23)).

Significant Impact Level (SIL): A screening tool used in the PSD program to determine whether a proposed source or modification will have a significant impact on ambient air quality. If the projected impact is below the SIL, the source is presumed to not cause or contribute to a violation of the NAAQS or PSD increments (40 C.F.R. § 51.165(b)(2)).

Stationary Source: Any building, structure, facility, or installation that emits or may emit a regulated NSR pollutant (40 C.F.R. § 52.21(b)(5)). NSR permitting requirements apply to stationary sources.