These memoranda are issued by EPA as general clarifications for issues related to the Guideline on Air Quality Models - Appendix W (PDF)(54 pp, 761 K, 01-17-2017) 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 PM_2.5 impacts for Permit Program Related Assessments and for NAAQS Attainment Demonstrations for Ozone, PM_2.5 and Regional Haze (PDF)(15 pp, 526 K, 08-04-2017)

Clarification on the AERMOD Modeling System Version for Use in SO₂ Implementation Efforts and Other Regulatory Actions (PDF)(4 pp, 366 K, 03-08-2017)

Clarification on the Approval Process for Regulatory Application of the AERMOD Modeling System Beta Options (PDF)(3 pp, 453 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 MB, 09-30-2014)

Interim Guidance on the Treatment of Condensable Particulate Matter Test Results in the PSD and NSR Permitting Programs(04-08-2014)

Clarification on the Use of ASOS Meteorological Data in AERMOD Dispersion Modeling (PDF)(35 pp, 1 MB, 03-08-2013)

Revised Policy to Address Reconsideration of Interpollutant Trading Provisions for Fine Particles (PM_2.5) (PDF)(5 pp, 368 K, 07-21-2011)

Clarification on AERSCREEN as Recommended Screening Model (PDF)(3 pp, 268 K, 04-11-2011)

Additional Clarification Regarding Applicability of Appendix W Modeling Guidance for the 1-hour NO₂ NAAQS (PDF)(27 pp, 453 K, 03-01-2011)

Applicability of Appendix W Modeling Guidance for the 1-hour SO₂ NAAQS (PDF)(5 pp, 288 K, 08-23-2010)

Applicability of Appendix W Modeling Guidance for the 1-hour NO₂ NAAQS (PDF)(16 pp, 285 K, 06-28-2010)

Modeling Procedures for Demonstrating Compliance with PM_2.5 NAAQS (PDF)(10 pp, 657 K, 03-23-2010)

Clarification on EPA-FLM Recommended Settings for CALMET (PDF)(12 pp, 601 K, 08-31-2009)

Clarification on Regulatory Status of CALPUFF for Nearfield Applications (PDF)(7 pp, 323 K, 08-13-2008)

Clarification on Regulatory Status of Proprietary Versions of AERMOD (PDF)(3 pp, 144 K, 12-11-2007)