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Revisions to Guideline on Air Quality Models Effective

  • 5/25/2017 8:42:00 AM
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Opportunity to comment on updated guidance

On May 22, 2017 the United States Environmental Protection Agency (EPA) announced that the revisions to air dispersion modeling requirements in Appendix W of 40 CFR Part 51 became effective.  The final rule includes several new or updated model options that help alleviate model over-prediction or allow for more appropriate source characterization.  Of particular importance to applicants in Iowa are the updates to the Nitrogen Dioxide Tier 2 and Tier 3 screening techniques, the optional adjustment of the surface friction velocity (Adjust-u*), and regulatory options to address plume rise for horizontal and capped stacks.

For additional information about the 2017 Appendix W final rule please visit EPA’s Support Center for Regulatory Atmospheric Modeling (SCRAM) website.

The Iowa DNR has incorporated these changes into various modeling guidance documents, which are available for informal comment now.  This information can be found on the Stakeholder Involvement page of the Air Quality Bureau’s website.


Please send any comments or questions to Brad Ashton at, or by phone at (515) 725-9527, by Wednesday June 7th.