CFR›Title 40›Chapter I›Part 81›Subpart A ContainsSection 81.1CorpusDaily eCFRDisplayed edition2026-05-07Last updated2026-05-07 Subpart A—Meaning of Terms Sections 81.1 § 81.1 Definitions. Next Appendix A to Part 81 Appendix A to Part 81—Air Quality Control Regions (AQCR's)