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New Source Review

Fact Sheet -- Proposed Clarifications and Modifications to Air Impact Modeling Procedures used for the New Source Review Prevention of Significant Deterioration Program


  • On May 24, 2007, the U.S. Environmental Protection Agency (EPA) proposed to refine several aspects of the method that may be used to calculate how air emissions from a new or modified industrial facility might impact an area. The New Source Review permitting program is one of the tools EPA, state, tribal and local air pollution control agencies rely upon to control emissions growth. 
  • This proposed rule would clarify how states and regulated sources may calculate increases in concentrations for the purposes of determining compliance with the PSD “increment.”
  • EPA is requesting public comment on:
    • how to estimate actual emissions for sources that consume the PSD increment;
    • using actual emissions to model short-term increments
    • using an alternative time period to model baseline concentration
    • how to treat subsequent air quality permits following a “variance” issued by the Federal Land Manager;
    • appropriate types of meteorological data and processing; and
    • appropriate years of meteorological data for modeling increment.
  • The proposed rule would improve implementation of the program by clarifying and codifying principles for determining major NSR applicability that we currently address through guidance only.  The proposed rules would provide greater regulatory certainty and reduce complexity without sacrificing the current level of environmental protection and benefit derived from the PSD program. 
  • EPA will accept comment on this rule for 60 days after publication in the Federal Register.


  • Congress established the NSR program as part of the 1977 Clean Air Act Amendments and modified it in the 1990 Amendments.  NSR is a preconstruction permitting program that serves two important purposes.
    1. First, it ensures the maintenance of air quality standards when factories, industrial boilers and power plants are modified or added.  In areas that do not meet the national air quality standards, NSR assures that new emissions do not slow progress toward cleaner air.  In areas that meet the standards, especially pristine areas like national parks, NSR assures that new emissions fall within air quality standards.
    2. Second, the NSR program assures that state of the art control technology is installed at new plants or at existing plants that are undergoing a major modification.
  • In areas that meet EPA’s national air quality standards (attainment areas), the New Source Review Prevention of Significant Deterioration (PSD) Program is in effect.  The PSD program protects clean air through a system of “increments.”  An increment is the maximum amount air concentrations of certain pollutants may increase above the baseline concentration in an area. 
  • PSD increments have been established for three pollutants – Sulfur Dioxide (SO2), Particulate Matter (PM), and Nitrogen Oxides (NOx).  A facility owner planning to build in an attainment area must apply for a  PSD permit.  As part of the application process, they must demonstrate that emissions from the proposed construction and operation of the facility will not cause or contribute to an increase above a maximum allowable concentration or increment for the target pollutant(s).
  • EPA has never developed detailed regulations establishing a specific methodology that facility owners or operators and reviewing authorities must use to calculate compliance with PSD increments.  Instead, increment analyses have been conducted by reviewing authorities based on guidance issued over the years.  In the absence of definitive requirements, sources and reviewing authorities have attempted to apply the available guidance to a wide range of situations resulting in different interpretations and approaches


  • Interested parties can download information on the proposal from EPA's Web site at: www.epa.gov/nsr.
  • Today's proposed action and other background information are also available either electronically in www.regulations.gov, EPA’s electronic public docket and comment system, or in hard copy at EPA’s Air and Radiation Docket and Information Center, Environmental Protection Agency, Room 3334, 1301 Constitution Avenue, NW, Washington, DC (Docket ID No. EPA-HQ-OAR-2006-0888). The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the Air and Radiation Docket and Information Center is (202) 566-1742.
  • HOW TO COMMENT: Comments will be accepted for 60 days beginning when this proposal is published in the Federal Register. All comments should be identified by Docket ID No. EPA-HQ-OAR-2006-0888 and submitted by one of the following methods:
    • www.regulations.gov
    • E-mail: a-and-r-docket@epa.gov
    • Facsimile (202) 566-1741
    • Mail (Air and Radiation Docket and Information Center, Environmental Protection Agency, Mailcode: 6102T, 1200 Pennsylvania Avenue, NW, Washington, DC 20460) or
    • Hand delivery (Air and Radiation Docket and Information Center, Environmental Protection Agency, Room 3334, 1301 Constitution Avenue, NW, Washington, DC).


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