Revision to the Guideline on Air Quality Models: Enhancements to the AERMOD Dispersion Modeling System and Incorporation of Approaches To Address Ozone and Fine Particulate Matter

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) 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. The proposed revisions to the Guideline include enhancements to the formulation and application of the EPA's AERMOD near-field dispersion modeling system and the incorporation of a tiered demonstration approach to address the secondary chemical formation of ozone and fine particulate matter (PM2.5) associated with precursor emissions from single sources. Additionally, the EPA proposes various editorial changes to update and reorganize information throughout the Guideline to streamline the compliance assessment process. Within this action, the EPA is also announcing the Eleventh 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.