Section 60.20a - Applicability(a) The provisions of this subpart apply upon publication of a final emission guideline under § 60.22a(a) if the guideline is published in the FEDERAL REGISTER after July 8, 2019. (1) Each emission guideline promulgated under this part is subject to the requirements of this subpart, except that each emission guideline may include specific provisions in addition to or that supersede requirements of this subpart. Each emission guideline must identify explicitly any provision of this subpart that is superseded.(2) Terms used throughout this part are defined in § 60.21a or in the Clean Air Act (Act) as amended in 1990, except that emission guidelines promulgated as individual subparts of this part may include specific definitions in addition to or that supersede definitions in § 60.21a .(b) No standard of performance or other requirement established under this part shall be interpreted, construed, or applied to diminish or replace the requirements of a more stringent emission limitation or other applicable requirement established by the Administrator pursuant to other authority of the Act (section 112, Part C or D, or any other authority of this Act), or a standard issued under State authority. 84 FR 32575 , July 8, 2019, as amended at 88 FR 80542 , Nov. 17, 2023 84 FR 32575 , 9/6/2019; 88 FR 80542 , 12/18/2023