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Ozone (2008 8-Hour Standard)

Current Status

Nonattainment – Moderate Area

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

Attainment Deadline

July 20, 2019 (pending approval of EPA’s proposed 1-year extension)


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.

While the region did not attain standard by July 20, 2018 based on a 3-year average of the 4th highest value for years 2015-2017, all monitors were at or below the 2008 standard of 75 parts per billion (ppb) for the 4th highest value in the attainment year (i.e. 2017), which qualified the region for a one-year attainment date extension.  This qualification occurred upon the Colorado Air Pollution Control Division (APCD) successfully completing an Exceptional Event (EE) demonstration that excluded two days in early September 2017 that were heavily influenced by wildfire smoke in the West.  This EE demonstration was submitted to EPA in May 2018 and EPA concurred with it in July 2018. As a result, EPA is proposing a one-year extension of the attainment date for the regional from July 20, 2018 to July 20, 2019.

Unfortunately, 2018 was one of the hottest and driest summers on record, and as a result ozone values were much higher.  As a result, the region does not qualify for a second one-year extension and, is facing a reclassification to a Serious nonattainment area by the end of 2019. If reclassified, this will require the development of a Serious Area Attainment Demonstration Plan showing compliance with the standard by the 2020 ozone season. This plan is anticipated to be due to EPA in early 2020, which means the plan must be developed by the end of 2019 to be endorsed by the RAQC Board and approved by the AQCC by summer 2020.


Current Planning Efforts

Strategy Evaluation


State Implementation Plan (SIP) Documents

MDM/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

Proposal of 1-year extension (to be added to Federal Register)

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