Guideline on Air Quality Models; Enhancements to the AERMOD Dispersion Modeling System

In this action, the Environmental Protection Agency (EPA) proposes to revise the Guideline on Air Quality Models ("Guideline"). The Guideline has been incorporated into EPA's regulations, satisfying a requirement under the Clean Air Act (CAA) section 165(e)(3)(D) for the EPA to specify, with reasonable particularity, models to be used in the Prevention of Significant Deterioration (PSD) program. It provides EPA-preferred models and other recommended techniques, as well as guidance for their use in predicting ambient concentrations of air pollutants. In this action, the EPA is proposing revisions to the Guideline, including enhancements to the formulation and application of the EPA's near-field dispersion modeling system, AERMOD, and updates to the recommendations for the development of appropriate background concentration for cumulative impact analyses. Within this action, the EPA is also announcing the Thirteenth Conference on Air Quality Modeling and invites the public to participate in the conference. The conference will focus on the proposed revisions to the Guideline, and part of the conference will also serve as the public hearing for these revisions.