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Air Quality

Air Pollutants - Ozone - Standards & Requirements

National Ambient Air Quality Standards for Ozone

Since the first ozone National Ambient Air Quality Standard (standard) was established in 1971, EPA has revised them several times. Using the tabs and links below you can find information on the current ozone standard and regulatory actions, as well as a detailed history of ozone standards.

1979 National Ambient Air Quality Standard for Ozone (February 8, 1979)
(Primary and Secondary Standards are the same)

Averaging Time Level (Parts per Million)
1 - Hour 1 0.12

1 This standard is met when there are no days in a calendar year with maximum hourly average levels above 0.12 ppm. On June 15, 2005 EPA revoked the 1-hour ozone standard in all areas, although some areas have continuing obligations under that standard.

History and Implementation of the 1971 1-hour Standard for Ozone

June 1996 EPA issued a three-volume criteria document encompassing hundreds of new scientific studies, finding "strong" scientific evidence of adverse health effects from ozone at levels allowed by the 1979 standard.
1995 EPA and 37 eastern states form the Ozone Transport Assessment Group work with stakeholders to study ozone transport for two years.
1994 EPA obtained a voluntary remand based on a promise to consider the newer studies.
1991 The number of counties designated for nonattainment reached 371. Concerned about the new science indicating adverse effects at levels allowed by that standard, the American Lung Association went to court to compel EPA to act.
1979 EPA revised the 1-hour standard to 0.12 ppm
1971 EPA established a 1-hour standard of 0.08 ppm

Additional Resources


For more information please contact the Bureau of Air Quality at (803) 898-4123 or by email.