On March 12, 2008, EPA revised the National Ambient Air Quality Standard for ozone, lowering the primary 8-hour standard from 84 ppb to 75 ppb and setting the secondary 8-hour standard identical to the primary standard. Challenges were filed by the State of Mississippi and industry groups claiming the new standard was too stringent, and by other states and environmental advocacy groups claiming that EPA and the Bush administration did not act on the recommendations of the Clean Air Scientific Advisory Committee (as required by the Clean Air Act) to lower the primary standard to 70 ppb.
On March 10, 2009, EPA requested that the court delay briefings on the consolidated lawsuits challenging the March 2008 revised ozone standard, citing its intent to "review the Ozone NAAQS Rule to determine whether the standards should be maintained, modified or otherwise reconsidered." On September 16, 2009, EPA filed a notice to the court that it would be reconsidering the Ozone NAAQS rule through comment and rulemaking with intent to propose by Dec. 21, 2009 and sign a final rule by Aug. 31, 2010. As part of this action, EPA agreed to delay the nonattainment designation process for the 75 ppb standard but will use the 2008 standard for new and modified sources in attainment areas. And, although the nonattainment designations under the 2008 standard would be not be issued in March 2010, as originally intended, SIP plans will be required by the end of 2013, as required under the 2008 standard.