---
kind: "unit"
title: "40"
title_heading: "Protection of Environment"
key: "chI/subchC/part51/subpartX"
level: "subpart"
label: "Subpart X"
heading: "Provisions for Implementation of 8-hour Ozone National Ambient Air Quality Standard"
release: "ecfr-current"
date: "2026-08-27"
url: "https://uscodex.org/cfr/40/chI-subchC-part51-subpartX"
sections_count: 20
---

# Subpart X — Provisions for Implementation of 8-hour Ozone National Ambient Air Quality Standard

Title 40 C.F.R. — Protection of Environment › Chapter I — Environmental Protection Agency › Subchapter C — Air Programs › Part 51 — Requirements for Preparation, Adoption, and Submittal of Implementation Plans

## Sections

- [§51.900. Definitions.](/cfr/40/51.900.md)
- [§51.901. Applicability of part 51.](/cfr/40/51.901.md)
- [§51.902. Which classification and nonattainment area planning provisions of the CAA shall apply to areas designated nonattainment for the 1997 8-hour NAAQS?](/cfr/40/51.902.md)
- [§51.903. How do the classification and attainment date provisions in section 181 of subpart 2 of the CAA apply to areas subject to § 51.902(a)?](/cfr/40/51.903.md)
- [§51.904. How do the classification and attainment date provisions in section 172(a) of subpart 1 of the CAA apply to areas subject to § 51.902(b)?](/cfr/40/51.904.md)
- [§51.905. How do areas transition from the 1-hour NAAQS to the 1997 8-hour NAAQS and what are the anti-backsliding provisions?](/cfr/40/51.905.md)
- [§51.906. Redesignation to nonattainment following initial designations for the 8-hour NAAQS.](/cfr/40/51.906.md)
- [§51.907. For an area that fails to attain the 8-hour NAAQS by its attainment date, how does EPA interpret sections 172(a)(2)(C)(ii) and 181(a)(5)(B) of the CAA?](/cfr/40/51.907.md)
- [§51.908. What modeling and attainment demonstration requirements apply for purposes of the 8-hour ozone NAAQS?](/cfr/40/51.908.md)
- [§51.909. Reserved](/cfr/40/51.909.md)
- [§51.910. What requirements for reasonable further progress (RFP) under sections 172(c)(2) and 182 apply for areas designated nonattainment for the 8-hour ozone NAAQS?](/cfr/40/51.910.md)
- [§51.911. Reserved](/cfr/40/51.911.md)
- [§51.912. What requirements apply for reasonably available control technology (RACT) and reasonably available control measures (RACM) under the 8-hour NAAQS?](/cfr/40/51.912.md)
- [§51.913. How do the section 182(f) NO X exemption provisions apply for the 8-hour NAAQS?](/cfr/40/51.913.md)
- [§51.914. What new source review requirements apply for 8-hour ozone nonattainment areas?](/cfr/40/51.914.md)
- [§51.915. What emissions inventory requirements apply under the 8-hour NAAQS?](/cfr/40/51.915.md)
- [§51.916. What are the requirements for an Ozone Transport Region under the 8-hour NAAQS?](/cfr/40/51.916.md)
- [§51.917. What is the effective date of designation for the Las Vegas, NV, 8-hour ozone nonattainment area?](/cfr/40/51.917.md)
- [§51.918. Can any SIP planning requirements be suspended in 8-hour ozone nonattainment areas that have air quality data that meets the NAAQS?](/cfr/40/51.918.md)
- [§51.919. Applicability.](/cfr/40/51.919.md)