An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Ground-level Ozone Pollution

Setting and Reviewing Standards to Control Ozone Pollution

On this page:

What are ozone standards?

National Ambient Air Quality Standards (NAAQS) for ground-level ozone, or ozone pollution, specify a maximum allowed measurement for ozone (O3) to be present in outdoor air. Limiting ozone pollution in the air protects human health and the environment.

In December 2020, EPA decided to retain the current ozone standards set in 2015:

Top of Page

How are the standards developed and reviewed?

The Clean Air Act requires EPA to periodically review all of the National Ambient Air Quality Standards to ensure that they provide adequate health and environmental protection, and to update those standards as necessary.

As part of the ozone standards review process, EPA publishes a detailed plan. The review plan describes all the scientific assessments and other documents that help EPA decide whether or not the current air quality standards for ozone are still protecting human health and the environment from harmful exposure. Based on this, EPA either changes the standards or keeps them the same.

Top of Page

What scientific and technical information supports review of the ozone standards?

The various documents published during the review process include multiple drafts of plans and assessments, reports from the Clean Air Scientific Advisory Committee (CASAC), and Federal Register notices.

Top of Page