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Ozone (2015 8-Hour Standard)



Current Status:

Nonattainment – Marginal Area

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

Attainment Deadline   

August 3, 2021



In April 2018, the U.S. Environmental Protection Agency (EPA) finalized designations, with an effective date of August 3, 2018.  The Denver Metro/North Front Range Area (DM/NFR) area was designated as a Marginal nonattainment area with an attainment date of August 3, 2021 (based on the three-year average of monitored ozone values from 2018 through 2020).  Though no Attainment Demonstration Plan is required for a Marginal nonattainment area, the RAQC is making the appropriate preparations in anticipation of a potential reclassification to Moderate in late 2021 if the region fails to attain. The RAQC has initiated modeling activities and will continue to lead control strategy evaluation efforts to determine what measures will be needed to attain the 2015 standard the end of 2020 and, if necessary, by the end of 2023.


Current Planning Efforts

Control Strategy Evaluations


State Implementation Plan (SIP) Documents

None at this time


Federal Rules and Actions


Proposal to Maintain Current Ozone Standard (85 FR 49830, Aug. 14, 2020)

Revised 8-Hour Ozone Standard (80 FR 65292, Oct. 26, 2015)

Designations and Classifications
State Implementation Plan Approvals

Infrastructure SIP Approval (85 FR 20165, Apr. 10, 2020)

Implementation Rules

Final Rule (81 FR 62998, Dec. 06, 2018)

Proposed Rule (81 FR 81276, Nov. 17, 2016)

RAQC Comments (Feb. 13, 2017)

Colorado Department of Public Health and Environment (CDPHE) Comments (Feb. 13, 2017)

Classification Rule (83 FR 10376, March 1, 2018)

Proposed Rule (81 FR 81276, Nov. 17, 2016)

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