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Information for the One-Hour Ozone Standard

Dallas skylineThe Environmental Protection Agency (EPA) implemented the one-hour standard in 1990. Under this standard, the ozone threshold value was 125 parts per billion (ppb), measured as one-hour average concentration. An area met this ozone National Ambient Air Quality Standard if there were no more than three exceedances at any one monitor in the region in a three-year period.

Four counties in the North Central Texas (NCT) region were designated as nonattainment for the one-hour ozone standard in 1991. Those counties were Collin, Dallas, Denton, and Tarrant. On June 15, 2005, the one-hour ozone standard was revoked and replaced by the eight-hour ozone standard. (see 1997 Eight-Hour Ozone Standard).

On October 31, 2006, the region demonstrated attainment of the one-hour ozone standard, althought it continues to be monitored due to EPA's anti-backsliding requirements. On October 16, 2008, the EPA issued a determination of attainment for the four one-hour nonattainment counties in NCT.

Additional Information

Information for the Eight-Hour Ozone Standard
Information for the One-Hour Ozone Standard [EPA]
Major Air Pollutants
National Ambient Air Quality Standards Table [EPA]




3/18/2016 JPL/CH

 North Central Texas Council of Governments | 616 Six Flags Drive P.O. Box 5888 Arlington, TX 76005-5888
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