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AERMOD is EPA’s preferred dispersion model for most near-field (≤ 50 km) applications, however, air dispersion science continues to advance. The need for technical improvements expressed by the stakeholder community that utilizes those advancements continue to be a motivation for the further development of AERMOD. Improvements to the scientific formulation of AERMOD, have been developed, tested, evaluated, and peer reviewed which improve model performance for specific source types and in certain situations. EPA is proposing revisions to the Guideline that would incorporate these improvements into AERMOD as part of the default regulatory formulation of the model. The proposed revisions to the Guideline would enable these formulation improvements to be used in a regulatory context without the approval for the use of a non-preferred alternative model by the appropriate EPA regional administrator and concurrence with the EPA’s Model Clearinghouse, as required per sections 3.2 and 3.3 of the current Guideline. EPA anticipates the proposed revisions will simplify compliance due to the improved model performance.