UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH TRIANGLE PARK, NC 27711 OCT 2 3 2015 OFFICE OF AIR QUALITY PLANNING AND STANDARDS MEMORANDUM SUBJECT: FROM : TO : Appendix W Webinars for State and Tribal Associations George M. Bridgers , Model Clearinghouse Director Air Quality Modeling Group , C439-01 Office of Air Quality Planning and Standards

# Chi**~** Proposed Regulatory Docket No. EPA-HQ-OAR-2015-0310 The Office of Air Quality Planning and Standards (OAQPS) participated in a series of conference calls with the National Association of Clean Air Agencies (NACAA), the Association of Air Pollution Control Agencies (AAPCA), and the National Tribal Air Association (NTAA) per each of these association ' s respective requests for a summary briefing on the proposed changes to the Guideline on Air Quality Models. The NACAA conference call was on August 6 , 2015; the AAPCA conference call was on August 25 , 2015; and the NTAA conference call was on October 20, 2015. For each of these engagements, the same presentation was provided to the participants and included summary slides from the material that the OAQPS presented at the 11th Conference on Air Quality Modeling. That presentation is included as an attachment to this docket submission. On each of the conference calls, participants asked general clarifying questions about the proposed rulemaking package , which were answered by OAQPS staff. Attachments: Proposal to Revise to the Guideline on Air Quality Models Overview and Status Briefing , August 6, 2015

Internet Address (URL) • http ://www . epa . gov Recycled/Recyclable •Printed with Vegetable Oil Based Inks on Recycled Paper ( Minimum 25 % Postconsumer)

# Proposal to Revise to the Guideline on Air Quality Models (Appendix W to 40 CFR Part 51) Overview and Status Briefing August 6 , 2015 (The m aterial for this briefing is publically available through previous EPA presentations, the Preamble and Fact Sheet for the proposed rulemaking,

and the 11 th Conference on Air Quality Modeling informational website. )

# Challenges to Our Current Air Quality Models
• States and sources report difficulty demonstrating compliance with 1 - hour NO 2 

### and SO 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. 

### • Sierra Club Petition Grant – Ozone and PM 2.5 

### .

– In January 2012, the EPA granted a petition submitted by the Sierra Club.

– In the petition grant, the EPA committed to engage in rulemaking to evaluate updates to Appendix W to 40 CFR 51 , and, as appropriate, incorporate new analytical techniques or models for ozone and secondary PM 2.5 for new and modified sources. 2

# Background • EPA’s Guideline on Air Quality Models ( Guideline) is published as Appendix W to 40 CFR Part 51. • EPA developed the Guideline to help EPA, States, and industry prepare and review new source permits and State or Tribal Implementation Plan revisions . • The Guideline is important because it specifies models for regulatory application and provides guidance for their use. • The Guideline provides a common basis for estimating the air quality concentrations of criteria pollutants used in assessing control strategies and developing emissions limits. 3

# Background • Originally published in 1978, the Guideline was last updated in 2003 and 2005 with the promulgation of CALPUFF as the preferred long - range transport dispersion model and AERMOD as the preferred nearfield dispersion model, respectively. • Per section 320 of CAA, EPA holds triennial conferences on air q uality m odeling to engage with public on appropriate modeling practices and, as appropriate, inform revisions to the Guideline. • The last modeling conference was the 10 th 

### Conference on Air Quality Modeling held in March 2012. 4

# Proposed Rulemaking and 11 th 

# Conference on Air Quality Modeling • On July 14, 2015, the EPA proposed to update to the Guideline on Air Quality Models.

– Published in the Federal Register on July 29, 2015. (80 FR 45340)

– Docket ID No. EPA- HQ -OAR-2015-0310

– 90-day public comment window ending on October, 27, 2015 . 

### • 11 th 

### Conference on Air Quality Modeling

– August 12 and 13, 2015 at the EPA RTP, NC Campus.

– Conference to focus on the proposed revisions to the Guideline.

– Serves as public hearing for NPRM as part of public comment period. Transcripts and presentation will be posted to Docket and on the 11 th Conference on Air Quality Modeling informational website. 

### • Final rulemaking anticipated in mid -2016. 5

# Appendix W: A Piece of the NSR Program Puzzle

6 6 **Bringing it together . . .** 

## PM2.5 SILs Rule Appendix W
Ambient Air & Related Policy Issues O3 SILs Rule

# Proposed Actions: AERMOD
• The EPA is proposing enhancements to the scientific formulation of the preferred near-field dispersion model, AERMOD, to address technical concerns expressed by the stakeholder community and improve model performance in its regulatory applications .

– 1. A proposed option incorporated in AERMET to adjust the surface friction velocity (u*) to address issues with AERMOD model overprediction under stable, low wind speed conditions . (ADJ_U*)

– 2. A proposed low wind option in AERMOD to address issues with model overprediction under low wind speed conditions. (LOWWIND3)

– 3. Modifications to AERMOD formulation to address issues with overprediction for applications involving relatively tall stacks located near relatively small urban areas. 7

# Proposed Actions: AERMOD ( Cont. )
• The EPA is proposing enhancements to the scientific formulation of the preferred near-field dispersion model, AERMOD, to address technical concerns expressed by the stakeholder community and improve model performance in its regulatory applications .

– 4 . Proposed regulatory default options in AERMOD to address plume rise for horizontal and capped stacks based on the July 9, 1993, Model Clearinghouse memorandum, with adjustments to account for the PRIME algorithm for sources subject to building downwash.

– 5. A proposed buoyant line source option, based on the BLP model, has been incorporated in AERMOD.

– 6. Proposed updates to the NO 2 Tier 2 and Tier 3 screening techniques coded within AERMOD, including the replacement of the Ambient Ratio Method (ARM) Tier 2 option with a revised ARM2 option and the replacement of the Plume Volume Molar Ratio Method (PVMRM) Tier 3 option with a revised PVMRM2 option . 8

# AERMET/AERMOD (v15181) Release
• At the same time as the NPRM, the regulatory version of the AERMOD Modeling System was revised to version 15181.

– Numerous bug fixes and limited enhancements were made to version 14134 as described in Model Change Bulletin #11.

– Included new “beta” options for LOWWIND3 and PVMRM2.

– Incorporated a buoyant line source option, based on BLP. 

### • Applicants with permits in process can still use AERMOD version 14134 but should review the MCB with the appropriate reviewing authority to determine if any of the changes would adversely impact concentration estimates and/or compliance status. Rerunning final results with version 15181 is preferred. • The proposed status of any “beta” or “non -default” option in the NPRM does not infer that they can be used immediately without appropriate justification and approval by the Regional Office with concurrence from the Model Clearinghouse. 9

# Proposed Actions: AERSCREEN & CALINE3
• The EPA is proposing AERSCREEN as the recommended screening model for simple and complex terrain for single sources and options for multi -source screening with AERMOD.

– AERSCREEN now includes inversion break- up and coastal fumigation which were previously parts of SCREEN3.


### • The EPA is proposing to replace the model known as CALINE3 for mobile source applications including fine particle pollution (PM 2.5 

### , PM 10

### ), and carbon monoxide (CO) hot-spot analyses based on evidence of a more scientifically sound basis for the use of AERMOD, improved model performance over CALINE3 , and its ability to use more recent and representative meteorological input data . 10

# Proposed Actions: Single- Source Impacts on Ozone and Secondary PM 2.5 • For this proposed revision to the Guideline, the EPA has determined that advances in photochemical modeling science indicate it is now reasonable to provide more specific, generallyapplicable guidance that identifies particular models or analytical techniques that may be used under specific circumstances for assessing the impacts of an individual source on ozone and secondary PM 2.5 

### . • The EPA believes photochemical grid models are generally most appropriate for addressing ozone and secondary PM 2.5 

### because they provide a spatially and temporally dynamic realistic chemical and physical environment for plume growth and chemical transformation . • The EPA is proposing a two-tiered demonstration approach for addressing single -source impacts on ozone and secondary PM 2.5 

### that will be used in concert with future demonstration tools ( e.g. , MERPs). 11

# Proposed Actions: CALPUFF & Met Data
• For long - range air quality assessments, the EPA is proposing to remove CALPUFF as a preferred model and recommending its use as a screening technique along with other Lagrangian models for addressing PSD increment beyond 50 km from a new or modifying source. ( This proposed change does not affect the EPA’s recommendation in the 2005 BART Guidelines to use CALPUFF in the BART determination process. )

• To provide more flexibility and improve the meteorological inputs used for regulatory modeling , the EPA is proposing to allow the use of prognostic meteorological data in AERMOD where there is no representative National Weather Service (NWS) station, and it is prohibitive or not feasible to collect adequately representative site -specific data .

– Mesoscale Model Interface Program (MMIF) 12

# Proposed Actions: Model Clearinghouse

• The EPA is proposing to codify the long -standing process of the Regional Offices consulting and coordinating with the Model Clearinghouse on all approvals of alternative models or techniques.

• While the Regional Administrators are the delegated authority to issue such approvals under section 3.2 of the Guideline, all alternative model approvals will only be issued after consultation with the EPA’s Model Clearinghouse and formal documentation through a concurrence memorandum which demonstrates that the requirements within section 3.2 for use of an alternative model have been met . 13

# Proposed Actions: Revisions to the Appendix W Reg Text
• The EPA is proposing to make modifications to section 8 of the Guideline regarding model inputs and background concentrations to provide much needed clarity associated with input and database selection for use in PSD and SIP modeling .

– More definitive definition of the appropriate modeling domain and how to best characterize the various contributions to air quality concentrations within that domain .

– Revised requirements on how to characterize emissions from nearby sources to be explicitly modeled for purposes of a cumulative impact assessment under PSD and new language regarding how to characterize direct and precursor emissions from modeled sources for SIP attainment demonstrations for ozone, PM2.5, and regional haze.

– Revised recommendations on how to determine background concentrations in constructing the design concentration, or total air quality concentration, as part of a cumulative impact analysis for NAAQS and PSD increments. 14

# Proposed Actions: Revisions to the Appendix W Reg Text ( Cont. )
• The EPA proposes to revise the discussion portion of section 9 to more clearly summarize the general concepts presented in earlier sections of the Guideline and to set the stage for the appropriate regulatory application of models and/or, in rare circumstances, air quality monitoring data.

– Strongly encourage adherence to the recommendations in section 9.2.1 of the proposed Guideline regarding development of a modeling protocol.


### • The EPA is proposing to make additional editorial changes to update and reorganize information throughout the Guideline. These revisions are not intended to meaningfully change the substance of the Guideline, but rather to make the Guideline easier to use . 15

# Reminder...
• The EPA proposed to update to the Guideline on Air Quality Models:

– Published in the Federal Register on July 29, 2015. (80 FR 45340)

– Docket ID No. EPA- HQ -OAR-2015-0310

– 90-day public comment window ending on October, 27, 2015 .


### • 11 th 

### Conference on Air Quality Modeling

– August 12 and 13, 2015 at the EPA RTP, NC Campus.

– Conference to focus on the proposed revisions to the Guideline.

– Serves as public hearing for NPRM as part of public comment period. Transcripts and presentation will be posted to Docket and on the 11 th Conference on Air Quality Modeling informational website. 16

# For More Information

• 11 th 

### Conference on Air Quality Modeling informational website: http :// www.epa.gov/ttn/scram/11thmodconf.htm


### • Proposed Rulemaking Docket (ID No. EPA- HQ - OAQ -2015 -0310): http ://www.regulations.gov/#! documentDetail;D=EPA- HQ -OAR-2015- 0310-0001


### • Conference Registration ( Not r equired but recommended ) 

### : http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/


### • Additional Questions About the Conference or P roposed Rulemaking: Bridgers.George@epa.gov 17