The need for additional clarification on addressing both the primary and secondarily

13 formed PM2.5 in NAAQS compliance demonstrations was heightened following an

14 administrative action on January 4, 2012, in which the EPA granted a petition submitted on

15 behalf of the Sierra Club on July 29, 2010 (U.S. EPA, 2012a). The Sierra Club petition

16 requested that the EPA initiate rulemaking to establish air quality models for ozone and PM2.5 for

17 use by all major sources applying for a PSD permit. In the petition grant, the EPA committed to

18 engage in rulemaking to evaluate updates to the Guideline on Air Quality Models as published as

19 Appendix W of 40 CFR 51 and, as appropriate, incorporate new analytical techniques or models

20 for ozone and secondary PM2.5. As a part of this commitment with the Sierra Club and in

21 compliance with Section 320 of the CAA, the EPA conducted the 10th Conference on Air Quality

Modeling (10th Modeling Conference) in March 2012. 3 At the 1 10th Modeling Conference, there

2 were invited presentations of ongoing research of single source plume chemistry and

3 photochemical grid modeling techniques, an overview presentation on the development of the

4 Draft Guidance for PM2.5 Permit Modeling, and several public forums and written comments

5 given pertaining to PM2.5 NAAQS modeling.

6 Based on the previous March 23, 2010, guidance memorandum, the NACAA Workgroup

7 final report recommendations, input from a mixture of stakeholders through numerous forums,

8 and recent applicant-submitted PM2.5 compliance demonstrations, the EPA prepared this Draft

9 Guidance on PM2.5 Permit Modeling. This draft guidance document recommends appropriate

10 technical approaches for conducting a PM2.5 NAAQS and increment compliance demonstration

11 which includes more adequate accounting for contributions from secondarily formed PM2.5

12 concentrations resulting from a proposed new or modifying source’s precursor emissions. In

13 keeping with the EPA’s commitments with the Sierra Club petition grant, the EPA is providing


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