Revisions 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) promulgates revisions to the Guideline on Air Quality Models (``Guideline''). The Guideline provides EPA's preferred models and other recommended techniques, as well as guidance for their use in estimating ambient concentrations of air pollutants. It is incorporated into the EPA's regulations, satisfying a requirement under the Clean Air Act (CAA) for the EPA to specify with reasonable particularity models to be used in the Prevention of Significant Deterioration (PSD) program. This action includes enhancements to the formulation and application of the EPA's preferred near-field dispersion modeling system, AERMOD (American Meteorological Society (AMS)/EPA Regulatory Model), 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. The EPA is changing the preferred status of and removing several air quality models from appendix A of the Guideline. The EPA is also making various editorial changes to update and reorganize information throughout the Guideline to streamline the compliance assessment process.