• Rule Summary
• Rule History
• Additional Resources

Rule Summary

In 2015, based on EPA’s review of the air quality criteria for ozone (O₃) and related photochemical oxidants and for O₃, EPA revised the levels of both standards. EPA revised the primary and secondary ozone standard levels to 0.070 parts per million (ppm), and retained their indicators (O₃), forms (fourth-highest daily maximum, averaged across three consecutive years) and averaging times (eight hours).

EPA made corresponding revisions in:

• data handling conventions for O₃
• changes to the Air Quality Index (AQI)
• regulations for the prevention of significant deterioriation (PSD) program
• establishing exceptional events schedules
• providing implementation information for the new standards

Rule History

• 10/26/2015 - Final Rule
• 12/17/2014 - Proposed Rule

Additional Resources

• Basic Information and Fact Sheets Regarding 2015 Revision to 2008 Ozone National Ambient Air Quality Standards (NAAQS)
• Interactive map showing the progress states, tribes, and EPA have made to meet the 1997 ground-level ozone standards 
• Interactive map showing the progress states, tribes and EPA have made to meet the 2008 ground-level ozone standards 
• Interactive map showing counties where measured ozone is above the 2015 standards and how EPA projects ozone air quality to improve through 2025 
• Ozone data tables 1997, 2008 and 2015 standards 
• Implementing the 2015 Ozone National Ambient Air Quality Standards (NAAQS) Memorandum
• Final Ozone NAAQS Regulatory Impact Analysis
• Scientific and Technical Documents Supporting the 2015 Revision to 2008 Ozone National Ambient Air Quality Standards (NAAQS)

Related Rules

• 1997 National Ambient Air Quality Standards (NAAQS) for Ozone (revoked) (PDF)
• Implementation of the 2008 National Ambient Air Quality Standards (NAAQS) for Ozone: State Implementation Plan (SIP) Requirements
• 2008 National Ambient Air Quality Standards (NAAQS) for Ozone