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Ozone (1997 8-Hour Standard)

Current Status

Marginal Nonattainment Area (Attaining as of 2009)

Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson, and portions of Weld and Larimer counties

Attainment Deadline

November 10, 2010



In 1997, EPA established a new, more stringent standard for ozone.  The new 8-hour standard was set at a level of 0.08 ppm (or 80 parts per billion) averaged over an eight-hour period. To take into account extreme and variable meteorological conditions that can influence ozone formation, the regional design value, which is the attainment test, is based on the three-year average of the fourth maximum 8-hour average ozone value at any given monitor.  Due to rounding, the EPA considers a violation of this standard to occur when the design value is equal to or greater than 0.085 ppm.

In December 2002, State and regional agencies with responsibilities for air quality and transportation planning in the Denver Metro Area joined EPA’s Early Action Compact (EAC) Program.  This allowed for a deferral of nonattainment designation based on the development of an Ozone Action Plan (OAP) to achieve attainment prior to the end of 2007.  However, in November 2007, due to a violation of the 1997 ozone standard, based on 2005-2007 monitor data, the 7-county Denver Metro Area plus parts of Larimer and Weld Counties were designated as Marginal nonattainment, with an attainment deadline of November 20, 2010.  An attainment SIP was submitted in December 2008 and the region has not violated this standard since 2008.  In 2011, EPA partially approved the Attainment Demonstration SIP.  In 2012, the 1997 ozone standard was revoked for purposes of Transportation Conformity and on April 6, 2015, the standard was fully revoked (80 FR 12264).


Plan Documents

Early Action Compact (EAC) Ozone Action Plan (Mar. 12, 2004)

Ozone Action Plan (Dec. 12, 2008)


Federal Rules and Actions

Standard and Revocation

Notice of Implementation of the Revoked 1997 8-Hour Ozone Standard (Aug. 31, 2020)

Revocation of standard (2008 SIP Requirements Rule (SRR)) (80 FR 12264, Mar. 6, 2015)

Revision of Ozone Standard (62 FR 38856, July 18, 1997)


Designations and Reclassifications

Attainment of 1997 Ozone NAAQS by Applicable Marginal Attainment Date (EPA R8, Feb. 8, 2019)

Change from Subpart 1 to Subpart 2 (77 FR 28424, May 14, 2012)

Designation of Marginal Nonattainment Area and Revocation of 1-hour Standard in EAC Areas (73 FR 17897,  Apr. 2, 2008)

Extension of Deferral of Designation to Nov. 20, 2007 (72 FR 53952, Sep. 21, 2007)

Extension of Deferral of Designation to Sept. 14, 2007 (72 FR 35356, June 28, 2007)

Extension of Deferral of Designation to July 1, 2007 (71 FR 69022, Nov. 29, 2006)

Extension of Deferral of Designation Dec. 31, 2006 (70 FR 50988, Aug. 29, 2005)

Early Action Compact Areas with Deferred Effective Dates 


State Implementation Plan (SIP) Approvals

EPA Approval of Colorado Infrastructure SIP (75 FR 31306, July 6, 2010, 75 FR 71028, Dec. 22, 2010, 76 FR 43906, Aug. 22, 2011, & 77 FR 1027, Feb. 8, 2012)

Approval of Attainment Demonstration and Motor Vehicle Emissions Budgets (MVEB) (76 FR 47443, Aug. 5, 2011)

Colorado Transport SIP (Dec. 12, 2008)

Approval of SIP Revisions (73 FR 8194, Feb. 13, 2008)

Approval of Early Action Compact (EAC) Attainment Demonstration (70 FR 28239, May 17, 2005)


Implementation Rules

Classifications Rule and Revocation for Transportation Conformity (77 FR 30160, May 21, 2012)

Implementation Rule (74 FR 40074, Aug. 11, 2009)

Implementation Rule – Phase I (69 FR 23951, April 30, 2004)



Other Documents of Interest

Ozone Summary Tables (updated weekly during ozone season)

EPA Approved Statutes and Regulations in the Colorado SIP

Colorado Air Quality Regulations


For more information, see RAQC’s “SIP Planning Process and Colorado SIP Summaries” document  (link)