Final rule · 2025-00946

Reference Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere (Chemiluminescence Method); Correction

The Environmental Protection Agency (EPA) is correcting a final rule published in the Federal Register on October 12, 2023, that became effective on November 13, 2023. The final rule updated the current ozone absorption cross-section to the recommended consensus- based value of 1.1329x10<SUP>-17</SUP> cm\2\ molecule<SUP>-1</SUP> or 304.39 atm<SUP>-1</SUP> cm<SUP>-1</SUP>. After publication, the EPA became aware of an error in the preamble text regarding the date for State, local, and Tribal monitoring agencies to complete implementation of the new ozone cross-section value, as well as a lack of clarity as to which entities the 2025 and 2026 implementation dates apply. With this action, the EPA is updating the final rule preamble and regulatory text to clarify the applicable implementation dates and the specific entities to which they apply. These corrections do not include any substantive changes to the final rule.