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Support Center for Regulatory Atmospheric Modeling (SCRAM)

Air Quality Models - Clarification Memos for Dispersion Models

These memoranda are issued by EPA as general clarifications for issues related to Appendix W (PDF)(45 pp, 803 K) and technical aspects of dispersion models, when necessary.

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.Use of Photochemical Grid Models for Single-Source Ozone and secondary PM2.5 impacts for Permit Program Related Assessments and for NAAQS Attainment Demonstrations for Ozone, PM2.s and Regional Haze (PDF) (15 pp, 513 K) - 08-04-2017

Clarification on the AERMOD Modeling System Version for Use in SO2 Implementation Efforts and Other Regulatory Actions (PDF) (4 pp, 357 K) - 03-08-2017

Clarification on the Approval Process for Regulatory Application of the AERMOD Modeling System Beta Options (PDF)(3 pp, 442 K) - 12-10-2015

Clarification on the Use of AERMOD Dispersion Modeling for Demonstrating Compliance with the NO2 National Ambient Air Quality Standard (PDF)(26 pp, 1.2 M) - 9-30-2014

Interim Guidance on the Treatment of Condensable Particulate Matter Test Results in the PSD and NSR Permitting Programs (PDF)(6 pp, 517 K) - 4-8-2014

Clarification on the Use of ASOS Meteorological Data in AERMOD Dispersion Modeling (PDF)(35 pp, 1.3 M) - 3-8-2013

Revised Policy to Address Reconsideration of Interpollutant Trading Provisions for Fine Particles (PM2.5) (PDF)(5 pp, 385 K) - 7-21-2011

Clarification on AERSCREEN as recommended screening model (PDF)(3 pp, 262 K) - 4-11-2011

Additional Clarification Regarding Applicability of Appendix W Modeling Guidance for the 1-hour NO2 NAAQS (PDF) (27 pp, 443 K) - 3-1-2011

Applicability of Appendix W Modeling Guidance for the 1-hour SO2 NAAQS (PDF)(5 pp, 281 K) - 8-23-2010

Applicability of Appendix W Modeling Guidance for the 1-hour NO2 NAAQS (PDF)(5 pp, 281 K) - 6-28-2010

Modeling Procedures for Demonstrating Compliance with PM2.5 NAAQS (PDF)(10 pp, 642 K) - 3-23-2010

Clarification on EPA-FLM Recommended Settings for CALMET (PDF)(12 pp, 587 K) - 8-31-2009

Clarification on Regulatory Status of CALPUFF for Nearfield Applications (PDF)(7 pp, 316 K) - 8-14-2008

Clarification on Regulatory Status of Proprietary Versions of AERMOD (PDF)(3 pp, 140 K) - 12-11-2007