1. Air Modeling Updates 2015 Region 4 Grants/Planning Meeting May 19-21, 2015 Atlanta, Georgia 1

2. “The Times, They are a-changin’” – Bob Dylan Standards are a-changin’ Guidance is a-changin’ Models are a-changin’ Modeling procedures are a- changin’ Technology is a-changin’ Modelers are a-changin’ 2

3. Important Modeling Issues Proposed Revisions to EPA’s guideline on Air Quality Models - 40 CFR Part 51, Appendix W PM2.5 Modeling Guidance Modeling Challenges for 1-hr SO 2 and NO 2 Standards Alternative Model Requests Addressing Modeled Violations Importance of Communication 3

4. 4 PSD Air Quality Modeling The primary purpose of an air quality dispersion modeling analysis is to demonstrate that all applicable National Ambient Air Quality Standards (NAAQS) and Prevention of Significant Deterioration (PSD) increments will be met after operation of the proposed construction or modification. Procedures outlined in the Code of Federal Regulation (CFR) Title 40, Part 51, Appendix W (Guideline on Air Quality Models) should be followed when conducting a modeling analysis. Many Region 4 State Implementation Plans (SIPs) use EPA Guideline on Air Quality Models in their permitting programs (e.g., AL, TN, KY…) as a regulation to follow in permitting Modeling Team AERMOD

5. Appendix W: A Piece of the NSR Program Puzzle 5 5 Bringing it together... PM2.5 SILs Rule Appendix W Ambient Air & Related Policy Issues O3 SILs Rule

6. Appendix W Proposed Revisions EPA is working on proposed revisions throughout all portions of Appendix W based on experiences gained since the last update in 2005. Clarification memorandums Guidance documents Model Clearinghouse actions Regional/State/Local modeling workshops 6

7. Appendix W Proposed Revisions Significant updates with respect to the tools and techniques for assessing secondarily formed PM 2.5 and O 3 as well as visibility and long range transport Consideration of all recently released beta options within AERMOD as promulgated options. ADJ_U*, LOWWIND1 & 2, and ARM2 Formulation other significant updates to the AERMOD Modeling System. AERSCREEN, BLP, PRIME downwash modifications, capped/horizontal stacks, AERCOARE, OCD & shoreline dispersion, industrial heat-island consideration (AISI), MMIF… Updates for other dispersion modeling applications such as mobile sources and transportation related. Rulemaking proposal projected for June 2015 ahead of the 11 th Conference on Air Quality Modeling. Final revised Appendix W publication in mid/late 2016. 7

8. 11 th Conference on Air Quality Modeling Will serve as the public hearing for the proposed Appendix W revisions rulemaking. Will be formally announced through publication in the Federal Register. Summary of Comments and Response to Comments documents will follow the 11 th MC. Tentatively looking at August 12-13, 2015, at the EPA Campus in RTP, NC. Also tentatively holding August 10-11, 2015, as possible dates for an abbreviated 2015 Regional/State/Local Modelers Workshop also at the EPA Campus in RTP, NC. 8

9. Guidance for PM 2.5 Permit Modeling Signed by Steve Page and released on May 20, 2014 during the middle of the 2014 RSL Modelers’ Workshop in Salt Lake City, UT. Available for download from the EPA’s SCRAM website: http://www.epa.gov/ttn/scram/ guidance/guide/Guidance_for _PM25_Permit_Modeling.pdf http://www.epa.gov/ttn/scram/ guidance/guide/Guidance_for _PM25_Permit_Modeling.pdf 9

10. Modeling for “New” 1-hr SO 2 and NO2 NAAQS States and sources report difficulty demonstrating compliance with 1-hour SO 2 and NO 2 NAAQS. Accuracy of models receiving greater scrutiny so need to address model inputs and science of our existing regulatory models. Past practices for NAAQS compliance demonstrations under NSR/PSD that may be “overly conservative” in some cases need to be re-evaluated 10

11. Change in Nature of NO 2 PSD Modeling Annual standard (53 ppb) –Permits generally used Tier 1 (full conversion) option 1-hr standard (100 ppb) –Tier 3 options generally necessary to demonstrate compliance –Requires additional input data to appropriately inform Tier 3 approaches (more costly & time- consuming) –Alternative Modeling Procedure - Necessitates approval from Regional office (more time- consuming) 11

12. PSD and NSR Modeling - Some issues Emissions rates for NAAQS/PSD Increment modeling NAAQS - Should use allowable, permitted or potential emission limits. Increment - Should use recent actual emissions Emission rate averaging times should correspond with the form of the ambient standard Maximum hourly emissions use for 1-hour SO 2 and NO 2 NAAQS Emissions Inventories PSD Applicability vs cumulative emissions inventory Background concentrations vs off-site/nearby sources Cumulative increment inventory; baselines, sources Alternative modeling approaches NO 2 Tier 3 approvals by Regional Administrator ADJ_u* or LOWWIND model options in AERMOD 12

13. Model predicted violation(s) in permit modeling? 1.Issue Permit, if all else is acceptable 2.State must resolve violation(s). 3.SIP revision could be required Yes 1.No Permit may be issued. 2.Unless compensating offsets for applicant’s significant emissions are required. 3.SIP revision could be required. Are Applicant’s concentration(s) < SIL(s)? Yes No Issue Permit, if all else is acceptable No Modeled Violations 13

14. 14 o Review modeling assumptions, review emissions inventory and emissions data. For example:  If the predictions are the result of emissions from off-property sources, the applicant/state may need to contact those sources to refine or update the emissions inventory.  Review sources characterizations (e.g., stack locations, operating parameters, property lines; and hours of operation, etc.) o Develop and submit to EPA a protocol or methodology to resolve modeled violations. o States have options on what, if any, control strategy is required to demonstrate compliance. o Ultimate goal is to show compliance with the NAAQS and/or PSD Increment in a timely manner. Resolving PSD Modeled Violations

15. Communication: Early and Often Communication on development of a permit demonstration is essential o State to Applicant  EPA approval of alternative modeling approaches  Modeling protocol development, data acquisition, etc.  Technical issues as they develop; an iterative process o State to State  Discussion and/or resolution of modeling violations especially if their sources are significant contributors  Source-specific modeling data o State to Region 4  EPA approval of alternative modeling approaches  Modeling protocol review  Issues discussions  Resolution of modeling violations o Extra time to prepare for and to resolve issues related to permit modeling 15

16. EPA Region 4 Modeling Contacts: Rick Gillam, 404/562-9049, gillam.rick@epa.gov Stan Krivo, 404/562-9123, krivo.stanley@epa.gov Richard Monteith, 404/562-8949, monteith.richard@epa.govgillam.rick@epa.govkrivo.stanley@epa.govmonteith.richard@epa.gov 16