In last month’s newsletter, we discussed that the U.S. EPA Administrator signed the final rule updating Appendix W to 40 CFR Part 51 – the Guideline on Air Quality Models. This final rule revised the scientific formulation in the AERMOD modeling system.
The final rule was published in the Federal Register (89 FR 95034) on November 29, 2024. Full text of the published version is available online and as a PDF. With this publication, the effective date for the rule is January 28, 2025. There is also a 1-year transition period through November 29, 2025, during which modeling protocols based on the 2017 version of the Guideline may be approved at the discretion of the appropriate reviewing authority.
Full technical details about the 2024 Appendix W Final Rule are available on the U.S. EPA webpage at https://www.epa.gov/scram/2024-appendix-w-final-rule. We encourage modelers to review the information for a full understanding of AERMOD’s technical options and capabilities.