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

PSD Permit Key Terms & Definitions

Attainment Area: An area that meets the National Ambient Air Quality Standards (NAAQS) for a specific pollutant, as determined by measurements of air quality. 42 U.S.C. §7407(d)(1)(A)(ii)

Best Available Control Technology (BACT): An emissions limitation based on the maximum degree of reduction of each pollutant subject to regulation under the Clean Air Act, taking into account energy, environmental, and economic impacts and other costs. BACT is determined on a case-by-case basis for major emitting facilities. 40 C.F.R. §52.21(b)(12)

Class I Area: Areas of special national or regional natural, scenic, recreational, or historic value for which the PSD regulations provide special protection. Class I areas include national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, scenic, recreational, or historic value. 40 C.F.R. §52.21(e)

Clean Air Act (CAA): The comprehensive federal law that regulates air emissions from stationary and mobile sources, establishes National Ambient Air Quality Standards (NAAQS) to protect public health and public welfare, and regulates emissions of hazardous air pollutants. 42 U.S.C. §7401 et seq.

Continuous Emissions Monitoring System (CEMS): The total equipment necessary for the determination of a gas or particulate matter concentration or emission rate using pollutant analyzer measurements and a conversion equation, graph, or computer program to produce results in units of the applicable emission limitation or standard. 40 C.F.R. §51.166(b)(43)

Criteria Air Pollutants: The six common air pollutants for which the EPA has established National Ambient Air Quality Standards (NAAQS) under the Clean Air Act. These pollutants are carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM10 and PM2.5), and sulfur dioxide (SO2). 40 C.F.R. Part 50

Emissions Offset: Reductions in emissions from existing sources that are used to compensate for emissions increases from new or modified sources in nonattainment areas. Offsets are required under the Nonattainment New Source Review (NNSR) program. 40 C.F.R. §51.165(a)(3)

Greenhouse Gases (GHGs): Gases that trap heat in the atmosphere, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). GHGs are regulated under the PSD program in certain circumstances. 40 C.F.R. §52.21(b)(49)

Lowest Achievable Emission Rate (LAER): The rate of emissions that reflects the most stringent emission limitation contained in the implementation plan of any State for a given class or category of source, or the most stringent emission limitation achieved in practice by such class or category of source, whichever is more stringent. LAER is required for new or modified major sources in nonattainment areas under the NNSR program. 40 C.F.R. §51.165(a)(1)(xiii)

Major Emitting Facility: Any stationary source that emits or has the potential to emit 100 tons per year or more of any regulated pollutant, or 250 tons per year or more of any regulated pollutant for certain categories of sources. Major emitting facilities are subject to the PSD permit requirements. 40 C.F.R. §52.21(b)(1)

Major Modification: Any physical change or change in the method of operation of a major stationary source that would result in a significant net emissions increase of any regulated pollutant. Major modifications are subject to PSD or NNSR permitting requirements, depending on the attainment status of the area. 40 C.F.R. §52.21(b)(2)

National Ambient Air Quality Standards (NAAQS): Standards established by the EPA under the Clean Air Act for pollutants considered harmful to public health and the environment. The EPA has set NAAQS for six principal pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter (PM10 and PM2.5), and sulfur dioxide. 40 C.F.R. Part 50

Nonattainment Area: An area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the National Ambient Air Quality Standards (NAAQS) for a specific pollutant. 42 U.S.C. §7407(d)(1)(A)(i)

Nonattainment New Source Review (NNSR): A preconstruction permitting program for new major sources or major modifications in nonattainment areas, designed to ensure that emissions from these sources do not hinder progress towards attaining the NAAQS. NNSR requires the installation of Lowest Achievable Emission Rate (LAER) technology and the acquisition of emissions offsets. 40 C.F.R. §51.165

Potential to Emit (PTE): The maximum capacity of a stationary source to emit a pollutant under its physical and operational design, considering any physical or operational limitations, including air pollution control equipment and restrictions on hours of operation or on the type or amount of material combusted, stored, or processed. 40 C.F.R. §52.21(b)(4)

Prevention of Significant Deterioration (PSD): A preconstruction permitting program designed to protect air quality in attainment areas by requiring new major sources or major modifications to install Best Available Control Technology (BACT) and demonstrate that the project will not cause or contribute to a violation of the NAAQS or applicable PSD increments. 40 C.F.R. §52.21

PSD Increment: The maximum allowable increase in ambient concentrations of a pollutant in an attainment area, measured from a baseline concentration. PSD increments are established for three area classifications (Class I, II, and III) and for three pollutants (PM10, SO2, and NO2). 40 C.F.R. §52.21(c)

PSD Permit: A permit issued under the Prevention of Significant Deterioration (PSD) program, authorizing the construction and operation of a new major source or major modification in an attainment or unclassifiable area. The PSD permit specifies emission limitations, monitoring requirements, and other conditions necessary to ensure compliance with the PSD regulations. 40 C.F.R. §52.21

Public Participation: The process by which the permitting agency provides notice to the public of a draft PSD permit, accepts public comments on the draft permit, and holds a public hearing if requested or if there is significant public interest. Public participation is an essential component of the PSD permit process. 40 C.F.R. §52.21(q)

Regulated Pollutant: Any pollutant for which a National Ambient Air Quality Standard (NAAQS) has been promulgated, as well as any constituents or precursors for such pollutants identified by the EPA. Regulated pollutants under the PSD program also include any pollutant that is subject to any standard promulgated under section 111 of the Clean Air Act, certain ozone-depleting substances, and greenhouse gases in certain circumstances. 40 C.F.R. §52.21(b)(50)

Significant Impact Level (SIL): A threshold concentration or level of ambient impact below which the EPA considers a source to have an insignificant effect on air quality. SILs are used to determine whether a source's impact is significant enough to warrant a more detailed air quality impact analysis. 40 C.F.R. §51.165(b)(2)

Significant Net Emissions Increase: For PSD purposes, a net emissions increase from a major modification that would equal or exceed the significant emission rates specified in the regulations for each regulated pollutant. A significant net emissions increase triggers PSD permitting requirements for the major modification. 40 C.F.R. §52.21(b)(23)

Stationary Source: Any building, structure, facility, or installation that emits or may emit a regulated pollutant. Stationary sources are subject to the PSD or NNSR permitting requirements if they qualify as major sources or undergo major modifications. 40 C.F.R. §52.21(b)(5)

U.S. Environmental Protection Agency (EPA): The federal agency responsible for implementing and enforcing the Clean Air Act and other environmental laws. The EPA administers the PSD permit program in partnership with state, local, and tribal air agencies. 42 U.S.C. §7401 et seq.

Unclassifiable Area: An area that cannot be classified as attainment or nonattainment on the basis of available information but for which the state or the EPA will initiate actions to change the status to attainment or nonattainment. PSD permitting requirements apply in unclassifiable areas. 42 U.S.C. §7407(d)(1)(A)(iii)

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