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Clarification Memos

Provides access to memoranda issued by EPA as general clarifications for issues related to Appendix W and technical aspects of dispersion models, when necessary.


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

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

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

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

Clarification on AERSCREEN as recommended screening model (4-11-2011)

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

Applicability of Appendix W Modeling Guidance for the 1-hour SO2 NAAQS (PDF) (8-23-2010)

Applicability of Appendix W Modeling Guidance for the 1-hour NO2 NAAQS (PDF) (6-28-2010)

Modeling Procedures for Demonstrating Compliance with PM2.5 NAAQS (PDF) (3-23-2010)

Clarification on EPA-FLM Recommended Settings for CALMET (PDF) (8-31-2009)

Clarification on Regulatory Status of CALPUFF for Nearfield Applications (PDF) (8-14-2008)

Clarification on Regulatory Status of Proprietary Versions of AERMOD (PDF) (12-11-2007)



Questions concerning the memos should be directed to Tyler Fox, Group Leader, Air Quality Modeling Group, at fox.tyler@epa.gov.

Office of Air and Radiation | Office of Air Quality Planning and Standards


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