# National Ambient Air Quality Standards for Ozone
> **Rule** · Final rule. · Published 2008-03-27 · Effective 2008-05-27 · 73 FR 16436
## Document
- **Document number:** E8-5645
- **Category:** air-emissions
- **Federal Register citation:** 73 FR 16436
- **CFR reference:** 40 CFR 50
- **Publication date:** 2008-03-27
- **Effective date:** 2008-05-27
- **EPA docket:** EPA-HQ-OAR-2005-0172
## Abstract

Based on its review of the air quality criteria for ozone (O<INF>3</INF>) and related photochemical oxidants and national ambient air quality standards (NAAQS) for O<INF>3</INF>, EPA is making revisions to the primary and secondary NAAQS for O<INF>3</INF> to provide requisite protection of public health and welfare, respectively. With regard to the primary standard for O<INF>3</INF>, EPA is revising the level of the 8-hour standard to 0.075 parts per million (ppm), expressed to three decimal places. With regard to the secondary standard for O<INF>3</INF>, EPA is revising the current 8- hour standard by making it identical to the revised primary standard. EPA is also making conforming changes to the Air Quality Index (AQI) for O<INF>3</INF>, setting an AQI value of 100 equal to 0.075 ppm, 8- hour average, and making proportional changes to the AQI values of 50, 150 and 200.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2008/03/27/E8-5645/national-ambient-air-quality-standards-for-ozone)
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