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Ozone (2008 8-Hour Standard)


Current Status

Nonattainment – Moderate Area (Proposed reclassification to Serious)

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

Attainment Deadline

July 20, 2018 (Current – Moderate Area)

July 20, 2021 (Anticipated – Serious Area)



In 2012, the Denver Metro/North Front Range Area (DM/NFR) area was designated as Marginal nonattainment for the 2008 National Ambient Air Quality Standard (NAAQS) for ozone.  On May 4th, 2016, due to the region not demonstrating attainment by the end of 2014 ozone season, the U.S. Environmental Protection Agency (EPA) published the final rule reclassifying the Denver Metro/North Front Range to a Moderate nonattainment area, which has an attainment deadline of July 20, 2018 and required the development and submittal of a State Implementation Plan (SIP).

A Moderate Area SIP for the 2008 8-Hour Ozone Standard was approved by the RAQC Board on June 30, 2016 and adopted by the Air Quality Control Commission on November 17, 2016.   The SIP was submitted to the EPA in May 2017 and a majority of it was approved July 2018.

As a Moderate nonattainment area the DM/NFR had an attainment date of July 20, 2018. Attainment was to be demonstrated based on certified ozone monitoring data from calendar years 2015-2017. The area failed to meet the 2008 standard during this time.  The area did have one year of data below the standard and, as such, a 1 year extension was requested by Colorado in 2018. The request, however, was withdrawn by the State on March 26, 2019 and the area is now facing reclassification to the next highest level. On August 8, 2019, the Environmental Protection Agency (EPA) proposed to reclassify the DM/NFR Nonattainment area to Serious under the 2008 ozone standard. The SIP would be due August 3, 2020 with an attainment deadline of July 20, 2021 based on 2018-2020 ozone season data.


State Implementation Plan (SIP) Documents

DM/NFR Moderate Area 2008 8-Hour Ozone Standard SIPApproved by the AQCC on November 17, 2016; Approved by EPA (83 FR 31068 – July 3, 2018)

Technical Support Documents (TSD)


Plan Development Documents

Moderate Area SIP Development and RAQC Proposal Process (2015-2016)

RAQC Cover Letter and Comments (July 7, 2016)

Ozone Modeling

2008 8-Hour Ozone Standard State Implementation Plan (SIP) Control Strategy Evaluation Effort

RAQC Public Input Plan (May 2016)


Federal Rules and Actions


Revised 8-Hour Ozone Standard (73 FR 60,  Mar. 27, 2008)

Proposed Rule (72 FR 132 – July 11, 2007)


Designations and Classifications

Proposed Reclassification to Serious (August, 15, 2019)

Proposal of 1-year extension (Revoked)

EPA Concurrence with 2017 Exceptional Events Demonstration (July 11, 2018)

Reclassification to Moderate (81 FR 26697, May 4, 2016)

EPA’s Final Action on Marginal Areas under 2008 Ozone NAAQS 

Proposed Action on Marginal Nonattainment Area (Aug. 19, 2015)

Designation of Marginal Nonattainment Area (77 FR 30088, May 21, 2012)


State Implementation Plan (SIP) Approvals

Final Approval of SIP (83 FR 31068, July 3, 2018)

Proposed SIP Approval (83 FR 67, Apr. 6, 2018)

Finding of Adequacy of Motor Vehicle Emissions Budgets (MVEB) (Jan. 30, 2018)

EPA Approval of Colorado Infrastructure SIP (80 FR 50205, Aug. 19, 2015 )

EPA Approval of Colorado Interstate Transport SIP (81 FR 7706, Feb. 16, 2016)

Proposed Rule (75 FR 11, Jan. 19, 2010)


Implementation Rules

State Implementation Plan Requirements Rule – Final (80 FR 44, Mar. 6, 2015)

Proposed Rule (78 FR 109, June 6, 2013)

Classifications Rule – Final (77 FR 98, May 21, 2012)

Proposed Rule (77 FR 30, Feb. 14, 2012)

Implementation of Ozone NAAQS Memo (Sep. 22, 2011)


Other documents of Interest

RAQC 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