Guidance for Ozone and Fine Particulate Matter Permit Modeling
On December 20, 2016, the Administrator signed a final rule that revised the Guideline on Air Quality Models. The final rule was published in the Federal Register on January 17, 2017, and the effective date of this action was deferred to May 22, 2017. The 2017 Guideline provides Environmental Protection Agency (EPA) recommended models and other techniques, as well as guidance for their use, for predicting ambient concentrations of air pollutants. For this final revision to the 2017 Guideline, the EPA determined that advances in chemical transport modeling science indicate it is now reasonable to provide more specific, generally-applicable guidance that identifies particular models or analytical techniques that may be used under specific circumstances for assessing the impacts of an individual source on secondary formation of ozone (O3) and fine particulate matter (PM2.5).
The EPA provided an initial “DRAFT Guidance for Ozone and Fine Particulate Matter Permit Modeling” to the state, local, and tribal air agencies, as well as the public, for consideration, review, and comment on February 10, 2020. Upon consideration of the comments received, and consistent with Executive Order 13990, the EPA decided to revise one important aspect of that draft guidance and, as a result, provided a “Revised Draft Guidance for Ozone and Fine Particulate Matter Permit Modeling” on September 20, 2021 for additional consideration, review and comment. The revision reflected a change in EPA policy with respect to determining which regulated New Source Review (NSR) pollutants should be included in Prevention of Significant Deterioration (PSD) compliance demonstration for O3 and PM2.5. We believe that change provided for more complete adherence to the related PSD regulatory requirements, considering the science of O3 and PM2.5 pollutant formation.
For more information regarding the evolution of the “Guidance on Ozone and Fine Particulate Matter Permit Modeling” and the comments received on the February 2020 draft and September 2021 revised draft guidance documents, please reference the respective embedded links above.
Based on the feedback received to both the draft and revised draft guidance documents and subsequent revisions, the EPA is now able to finalize and provide the “Guidance on Ozone and Fine Particulate Matter Permit Modeling” in a final form to the state, local, and tribal air agencies, as well as the public. This guidance document reflects the EPA's recommendations for how a stationary source seeking a PSD permit may demonstrate that it will not cause or contribute to a violation of the National Ambient Air Quality Standards for ozone (O3) and fine particulate matter (PM2.5) and PSD increments for PM2.5, as required under Section 165(a)(3) of the Clean Air Act and 40 CFR sections 51.166(k) and 52.21(k).
We are maintaining the “holistic” compliance demonstration approach and all other recommendations from the revised draft guidance. We have made a few clarifications and associated updates to the final guidance based on the external comments, but the overall nature of the final guidance remains unchanged from the revised draft guidance.
This final guidance is now the full replacement to the previous “Guidance for PM2.5 Permit Modeling” (2.27 MB, 05-22-2014, 454-B-14-001) reflecting the 2017 revisions to the Guideline and incorporation of appropriate sections for addressing O3 along with, or in additional to, PM2.5. The final guidance also fully replaces the February 10, 2020 draft and September 20, 2021 revised guidance documents and the recommendations contained within.
The EPA still highly recommends consultation with the appropriate permitting authority and EPA Regional Office for any permit applicants developing O3 and PM2.5 PSD compliance demonstrations. Such consultation can resolve potential issues early in the permitting process and alleviate unnecessary work with developing an acceptable compliance demonstration.
The EPA conducted a release webinar on Thursday, August 11th at 3pm EDT to provide an overview of the “Guidance for Ozone and Fine Particulate Matter Permit Modeling” and allow for an open exchange on the final version of the guidance.
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Additional Technical Support Material:
|Addressing Single-Source Impacts on Ozone and Secondary PM2.5|
In order to provide the user community flexibility in estimating single-source secondary pollutant impacts and given the emphasis on the use of chemical transport models for these purposes, the EPA is finalizing a two-tiered demonstration approach for addressing single-source impacts on ozone and secondary PM2.5. The first tier involves use of technically credible relationships between precursor emissions and a source’s impacts that may be published in the peer-reviewed literature; developed from modeling that was previously conducted for an area by a source, a governmental agency, or some other entity and that is deemed sufficient; or generated by a peer-reviewed reduced form model. The second tier involves application of more sophisticated case-specific chemical transport models (e.g., photochemical grid models) to be determined in consultation with the EPA Regional Office and conducted consistent with new EPA single-source modeling guidance. The appropriate tier for a given application should be selected in consultation with the appropriate reviewing authority and be consistent with EPA guidance.