Appendix B: General Guidance on Use of Dispersion Models 1 for Estimating Primary

2 PM2.5 Concentrations


4 This appendix provides general guidance on the application of dispersion models for

5 estimating ambient concentrations of PM2.5 associated with direct emissions of primary PM2.5.

6 This guidance is based on and is consistent with the EPA’s Guideline on Air Quality Models,

7 published as Appendix W of 40 CFR Part 51, and focuses primarily on the application of

8 AERMOD, the EPA’s preferred dispersion model for most situations. Appendix W is the

9 primary source of information on the regulatory application of air quality models for State

10 Implementation Plan (SIP) revisions for existing sources and for New Source Review (NSR) and

11 Prevention of Significant Deterioration (PSD) programs. There will be applications of

12 dispersion models unique to specific areas, (i.e., there may be areas of the country where it is

13 necessary to model unique specific sources or types of sources). In such cases, there should be

14 consultation with the state, or appropriate reviewing authority with the appropriate Regional

15 Office modeling contact to discuss how best to model a particular source


17 Recently issued EPA guidance of relevance for consideration in modeling for PM2.5

18 includes:

19 “Model Clearinghouse Review of Modeling Procedures for Demonstrating Compliance

20 with PM2.5NAAQS” February 26, 2010 (U.S. EPA, 2010a);

21 ”Modeling Procedures for Demonstrating Compliance with PM2.5 NAAQS” March 23,

22 2010 (U.S. EPA, 2010b); and

23 “Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM2.5 and

24 PM10 Nonattainment and Maintenance Areas” December 2010 (U.S.EPA, 2010c).


26 The guidance listed above, in addition to other relevant support documents can be found on the


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