ACTION: Final rule. SUMMARY: 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. DATES: This rule is effective December 9, 2005. As proposed, beginning November 9, 2006, the new model—AERMOD— should be used for appropriate application as replacement for ISC3. During the one-year period following this promulgation, protocols for modeling analyses based on ISC3 which are submitted in a timely manner may be approved at the discretion of the appropriate Reviewing Authority. Applicants are therefore encouraged to consult with the Reviewing Authority as soon as possible to assure acceptance during this period. ADDRESSES: All documents relevant to this rule have been placed in Docket No. A–99–05 at the following address: Ai