Revised Draft Guidance for Ozone and Fine Particulate Matter Permit Modeling

Background

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The EPA provided an initial “DRAFT Guidance for Ozone and Fine Particulate Matter Permit Modeling” to the state, local, and tribal air agencies, as well as the public, for consideration, review, and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received, and consistent with Executive Order 13990, the EPA has decided to revise one important aspect of that draft guidance and, as a result, is posting a revised version of the February 20, 2020 draft guidance for additional public comment. The revision reflects 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) air quality assessments for O3 and PM2.5. We believe this change provides for more complete adherence to the related PSD regulatory requirements, considering the science of O3 and PM2.5 pollutant formation.

The revised draft guidance provides an update and replacement to the previous “Guidance for PM2.5 Permit Modeling” to reflect the 2017 revisions to the Guideline and to incorporate appropriate sections for O3. The revised draft guidance also fully replaces the previous February 10, 2020 draft guidance and the recommendations contained within that draft guidance. Until a final version of the guidance is released, consultation with the appropriate permitting authority and appropriate EPA Regional Office is highly recommended for any permit applicants developing O3 and PM2.5 PSD compliance demonstrations.

Revised Draft Guidance

The EPA is providing the attached “ Revised DRAFT Guidance for Ozone and Fine Particulate Matter Permit Modeling (pdf) (4.09 MB, 09/20/2021, 454-P-21-001) ” (142 pp, 4.1 MB, 09-20-2021, 454-P-21-001) to the state, local, and tribal air agencies, as well as the public, for consideration, review and comment. 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).

The EPA is requesting that comments on the revised draft guidance be provided by Friday, November 19, 2021. This allows at least 60 days for consideration, review, and comment on the material presented in the draft guidance. Comments should be electronically submitted directly to George Bridgers at bridgers.george@epa.gov. Following the close of the comment period, the EPA will take into consideration all the feedback and comments submitted and will further engage with the regulatory air quality modeling community on further clarifications, potential amendments, and considerations for additions to the final guidance documentation.

Webinar

The EPA conducted a webinar on Thursday, October 14th at 3pm EDT to provide an overview of the “Revised DRAFT Guidance for Ozone and Fine Particulate Matter Permit Modeling” and allow for an open exchange on the revised documentation.

Comments Received

Thirteen comment packages regarding the Revised Draft Guidance for Ozone and Fine Particulate Matter Permit Modeling were submitted to the EPA for consideration.

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.

Supporting Documentation

Support Center for Regulatory Atmospheric Modeling (SCRAM)

Contact Us about Air Quality Models
Contact Us about Air Quality Models to ask a question, provide feedback, or report a problem.
Last updated on January 28, 2025