Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions

EPA's Guideline on Air Quality Models ("Guideline") addresses the regulatory application of air quality models for assessing criteria pollutants under the Clean Air Act. In today's action we promulgate several additions and changes to the Guideline. We recommend a new dispersion model--AERMOD--for adoption in appendix A of the Guideline. AERMOD replaces the Industrial Source Complex (ISC3) model, applies to complex terrain, and incorporates a new downwash algorithm--PRIME. We remove an existing model--the Emissions Dispersion Modeling System (EDMS)--from appendix A. We also make various editorial changes to update and reorganize information.