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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.

1997 National Ambient Air Quality Standard for Ozone (July 17, 1997)
(Primary and Secondary Standards are the same)

Averaging Time Level (Parts per Million)
8 - Hour 1 0.08

1 To meet this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone levels measured at each monitor within an area each year cannot exceed 0.08 ppm.

History and Implementation of the 1997 8-hour standard for Ozone

December 26, 2012 EPA published a final approval (77 FR 75862) of the redesignation plan for the South Carolina portion of the Charlotte-Gastonia-Rock Hill NC-SC (Metrolina) nonattainment area. This redesignated the area from nonattainment to attainment. EPA also approved South Carolina’s 1997 8-hour ozone NAAQS maintenance plan, including the associated motor-vehicle emissions budget (MVEB), into the South Carolina State Implementation Plan (SIP).
November 15, 2012 EPA published a proposed approval (77 FR 68087) of the redesignation plan for the South Carolina portion of the Metrolina nonattainment area. If finalized, this action would redesignate the area from nonattainment to attainment. EPA is also proposing to approve South Carolina’s 1997 8-hour ozone NAAQS maintenance plan, including the associated MVEB, into the SIP.
June 25, 2012 EPA published a direct final rule (77 FR 37812) approving the emissions statement requirement for the York County portion of the April 29, 2010, Metrolina Nonattainment Area. This direct final rule is effective August 24, 2012, unless EPA receives adverse comments on the parallel proposal (77 FR 37841) by July 25, 2012.
May 21, 2012 EPA published a final rule implementing the 2008 ozone standard, (77 FR 30160) which includes providing for the revocation of the 1997 ozone standard for transportation conformity purposes to occur 1 year after the effective date of designation (July 20, 2012) for the 2008 ozone standard, which will be July 20, 2013.
May 18, 2012 EPA published a final rule (77 FR 29540) to approve the ozone 2002 base year emissions inventory portion of the attainment demonstration for the 1997 ozone standard. The direct final rule is effective July 17, 2012, unless EPA receives adverse comment by June 18, 2012.
January 12, 2012 On January 12, 2012, at the request of EPA Region 4, DHEC withdrew the attainment demonstration for the Metrolina Nonattainment Area except for the reasonable further progress plans and emissions inventories.
November 15, 2011 EPA has issued a "clean data determination" (76 FR 70656) for the Metrolina Nonattainment Area because current data show that the area is now meeting the 1997 8-hour ozone standard.
June 1, 2011 DHEC submitted the Redesignation Demonstration and Maintenance Plan for the York County portion of the Metrolina Nonattainment Area.
April 2010 DHEC submitted the final revised attainment demonstration and supplemental information.
November 2009 DHEC sent a letter to EPA indicating that supplemental information would be prepared and requesting that the approval process for the 2007 attainment demonstration begin.
October 2009 EPA presented the option of resubmitting the original attainment demonstration from 2007 with additional weight-of-evidence and 2009 air quality data.
May 2009 EPA issued a "Finding of Failure to Submit" the attainment demonstration because it had been withdrawn.
December 2008 DHEC responded to EPA that disapproval of the attainment demonstration would have been premature, and that the state would plan to withdraw the attainment demonstration and submit a revised version by November 30, 2009.
November 2008 DHEC received a letter from EPA predicting that the York County portion of the Metrolina Nonattainment Area would fail to achieve attainment by the summer 2009 deadline. EPA indicated it would disapprove the SIP's attainment demonstration unless DHEC requested to reclassify to a higher nonattainment classification.
June 2007 DHEC submitted its plan to meet the 1997 health-based 8-hour ozone standard to EPA.
April 15, 2004 EPA finalized the Ozone designations and basic implementation rule.
December 2003 EPA responded to states and tribes describing intended modifications to their recommended designations - 506 counties were included. EPA proposed the Clean Air Interstate Rule to help areas in the US meet the 8-hour ozone standard.
July 2003 EPA proposed the clean air ozone implementation rule with options for how areas would transition from the 1-hour ozone standard to the 8-hour ozone standard. States and tribes recommended designations - 412 counties were included.
2002 EPA began the process by which states (governors) and tribes submit recommendations for what areas would be designated nonattainment (failing to meet the 1997 ozone standard).
2001 The U.S. Supreme Court unanimously upheld the constitutionality of the Clean Air Act as EPA had interpreted it in setting the 1997 health-protective air quality standard. The Supreme Court also reaffirmed EPA's long-standing interpretation that it must set these standards based solely on public health considerations without consideration of costs.
1999 The DC Circuit Court of Appeals sent the 1997 standard back to EPA for further study. EPA appealed.
July 18, 1997 EPA revised the standard for ozone, replacing the 1979 standard with an 8-hour standard set at 0.08 ppm. Three states and dozens of industry plaintiffs quickly challenged the new standards.

Additional Resources


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