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Support Center for Regulatory Atmospheric Modeling (SCRAM)

Draft Guidance for Ozone and Fine Particulate Matter Permit Modeling


On December 20, 2016, the Administrator signed a final rule that revises the Guideline on Air Quality Models(PDF, 54 pp, 761 K, 01-17-2017). 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 Guideline provides 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 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 ozone and secondary PM2.5.

Draft Guidance:

The Environmental Protection Agency (EPA) is providing the DRAFT Guidance for Ozone and Fine Particulate Matter Permit Modeling (PDF)(137 pp, 5 MB, 02-10-2020, 457-P-20-002) to the state, local, and tribal air agencies, as well as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 Prevention of Significant Deterioration (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The EPA is requesting that comments on the draft guidance be provided by Friday, April 17, 2020. This allows at least 60 days for consideration, review, and comment on the material presented in the draft guidance.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 me at 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.


The EPA conducted a webinar on Thursday, March 12th at 3pm EDT to provide an overview of the Draft Guidance for Ozone and Fine Particulate Matter Permit Modeling allowing for an open exchange on the guidance documentation.

Comments Received:

Fourteen comment packages regarding the Draft Guidance for Ozone and Fine Particulate Matter Permit Modeling were submitted to the EPA by Friday April 17, 2020 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 finaled 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