This section provides recommendations on modeling techniques and guidance for estimating pollutant concentrations in order to assess control strategies and determine emission limits. These recommendations were originally published in April 1978 as the "Guideline on Air Quality Models" and were incorporated by reference in the regulations for the Prevention of Significant Deterioration of Air Quality, Title 40, Code of Federal Regulations (CFR) sections 51.166 and 52.21 in June 1978 [Federal Register, 43 (118), 26 382-26 388]. The purpose of these guidelines is to promote consistency in the use of modeling within the air quality management process. These guidelines are periodically revised to ensure that new model developments or expanded regulatory requirements are incorporated. This section provides guidance associated with permit modeling and is divided into three components: Appendix W Guidance, Screening Guidance, and Other Permit Modeling Guidance.
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|Appendix W Guidance
Appendix W (PDF)(54 pp, 742 K) - 40 CFR Part 51 Appendix W (January 2017)
Appendix W (PDF)(45 pp, 803 K) - 40 CFR Part 51 Appendix W (November 2005)
Preferred/Recommended Models listed in Appendix W - a list of referred and recommended models as provided in Appendix W.
Use of Alternative Models - A list of dispersion models for use on a case-by-case basis with approval by reviewing authority.
Air Quality Analysis Checklist (PDF)(13 pp, 74 K, 2016) - The Air Quality Analysis Checklist assists the regulatory reviewer in assuring that important aspects of the NSR/PSD compliance demonstrations for NAAQS and PSD increments are accounted for and appropriately examined. Additionally, this checklist is useful for those conducting these regulatory demonstrations by identifying the necessary pieces of information required to assure an appropriate air quality assessment. A previous version of the Checklist (14 pp, 111 K ) formerly appeared as Appendix C of the "Guideline on Air Quality Models" as explained in the Explanatory Note (TXT)(1 K).
Clarification Memos - Provides access to memoranda issued by EPA as clarifications of Appendix W and technical aspects of dispersion modeling in general.
|Other Permit Modeling Guidance
|Guidance for PM2.5 Permit Modeling (PDF) (144 pp, 2.3MB) - May 2014. EPA 454/B-14-001. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards.
Draft Guidance for PM2.5 Permit Modeling (116 pp, 4.6MB) - March 2013. EPA 454/D-13-001. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards.
- There is an accompanying PM2.5 SILs/SMC Court Decision Question and Answer Document (PDF) (PDF, 99KB) that provides additional context for the Draft Guidance for PM2.5 Permit Modeling with regards to the January 22, 2013, United States Court of Appeals for the District of Columbia Circuit decision concerning PM2.5 SILs and SMC.
- Area Source Estimated Concentrations Related Update (PDF)(1 pg, 25 K)
Guideline for Determination of GEP Stack Height (PDF)(101 pp, 4 M, 1985) - Technical Support Document
Protocol for Determining the Best Performing Model (ZIP) (124KB)
Guidance Concerning the Implementation of the 1-hour SO2 NAAQS for the Prevention of Significant Deterioration Program (PDF)(19 pp, 971 K, 2010)
Guidance Concerning the Implementation of the 1-hour NO2 NAAQS for the Prevention of Significant Deterioration Program (PDF)(30 pp, 1.3 M, 2010)
Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas (PDF) (160 pp, 3.0 M, About PDF) - November 2015. EPA-420-B-15-084. U.S. Environmental Protection Agency, Office of Transportation and Air Quality.
Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas - Appendix (PDF) (82 pp, 1.0 M, About PDF) - November 2015. EPA-420-B-15-084-Appendices. U.S. Environmental Protection Agency, Office of Transportation and Air Quality.