2060-AV63 202304 Unified Agenda of Federal Regulatory and Deregulatory Actions 2060 Office of Air and Radiation OAR 2000 Environmental Protection Agency EPA Revision to 40 CFR Part 50, Appendix D, "Reference Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere (Chemiluminescence Method)"

The EPA is taking this action to revise the current ozone absorption cross-section stated in appendix D to the recently revised international consensus-based cross-section value of 1.1329x10−17 cm2 molecule−1 or 304.39 atm-1 cm-1 with an uncertainty of 0.94 atm-1 cm-1, which is 1.2% lower than the current value of 308 atm-1 cm-1. The cross-section value serves as the basis for calculating and calibrating ozone concentrations using the ultraviolet (UV) photometric method of analysis. The EPA is changing the current absorption cross-section to the revised consensus-based value because it reflects an advancement in science and measurement technology that will improve the bias and reduce the uncertainty in this value.

]]> Substantive, Nonsignificant Previously Published in The Unified Agenda Final Rule Stage No No 40 CFR 50 42 U.S.C. 7401 to 7671q. No NPRM 02/24/2023 88 FR 11835 Final Rule 07/00/2023 EPA-HQ-OAR-2022-0007. No No None No No No No Joann Rice 2060 Office of Air and Radiation OAR 919 541-3372 919 541-1903 Rice.Joann@epamail.epa.gov C304-06, Research Triangle Park NC 27711