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Information for the 1-Hour Ozone NAAQS

Dallas skylineThe Environmental Protection Agency (EPA) implemented the 1-hour National Ambient Air Quality Standards (NAAQS) for ozone 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 NAAQS 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 1-hour ozone NAAQS in 1991. Those counties were Collin, Dallas, Denton, and Tarrant. On June 15, 2005, the 1-hour ozone NAAQS was revoked and replaced by the 8-hour ozone NAAQS. (see 1997 Ozone NAAQS).

On October 31, 2006, the region demonstrated attainment of the 1-hour ozone NAAQS , although 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 1-hour Ozone NAAQS [EPA]
Information for the 8-hour Ozone NAAQS
Major Air Pollutants
National Ambient Air Quality Standards Table [EPA]




4/27/2018 JPL/CH %Trans

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