Ozone Air Quality Standards

Announcements

March 12, 2008
EPA significantly strengthens the National Ambient Air Quality Standards for ground-level ozone.

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The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for ground-level ozone and five other criteria pollutants. The Clean Air Act established two types of national air quality standards for ground-level ozone.

Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly.

Secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings.

The Clean Air Act requires EPA to review the latest scientific information and standards every five years. Before new standards are established, policy decisions undergo rigorous review by the scientific community, industry, public interest groups, the general public and the Clean Air Scientific Advisory Committee (CASAC). More about the process of reviewing the standards.

National Ambient Air Quality Standards for Ground-level Ozone

	Primary Standards		Secondary Standards
	Level	Averaging Time	Level	Averaging Time
Ozone	0.075 ppm (2008 std)	8-hour ¹	Same as Primary
	0.08 ppm (1997 std)	8-hour ²	Same as Primary
	0.12 ppm	1-hour ³ (Applies only in limited areas)	Same as Primary

¹ To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.075 ppm. (effective May 27, 2008)

² (a) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.
(b) The 1997 standard—and the implementation rules for that standard—will remain in place for implementation purposes as EPA undertakes rulemaking to address the transition from the 1997 ozone standard to the 2008 ozone standard.

³ (a) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is < 1.
(b) As of June 15, 2005 EPA revoked the 1-hour ozone standard in all areas except the 8-hour ozone nonattainment Early Action Compact (EAC) areas.

Learn more about the national ambient air quality standards

Related Documents

Documents from Review Completed in 2008

Documents from Review Completed in 1997

For more information

Process of Reviewing the Standards
History of Ground-level Ozone Standards
Technical Information
Greenbook (detailed design and implementation information)
Ozone Designations
Ozone Implementation

Ozone Air Quality Standards

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