On December 20, 2016, the U.S. EPA Administrator signed a final rule that revises the Guideline on Air Quality Models (40 CFR Part 51, Appendix W). The Guideline identifies EPA-recommended models and other techniques as well as guidance for their use in predicting ambient concentrations of air pollutants. EPA’s finalized changes enhance the formulation and application of the agency’s AERMOD dispersion model, prescribe modeling techniques for secondarily formed fine particle and ozone pollution for single sources, and make various editorial improvements. View the pre-Federal Register version of the Final Rule here. The FR version will be out in the next several weeks.
National and state air quality regulations rely upon EPA modeling guidance for performing dispersion modeling studies as part of routine air permitting and other regulatory air studies. This revision to the Guideline will dictate future dispersion modeling techniques for major permit actions (new and modified permits). While some states do not have any state specific guidance and interpret the guidelines on an as-needed basis for projects, other states will have their own interpretations and specific guidance. Important new guidance contained in the recent changes includes modeling actual emissions instead of allowable emissions for regional inventory sources, increased guidance on accounting for background concentrations, use of adjusted turbulence (which will lower concentrations in most cases), low wind speed adjustments, and alternate NO2/NOx conversions.
For questions on the recent changes or assistance with dispersion modeling, contact your local Trinity office at (800) 229-6655 or George Schewe at firstname.lastname@example.org.