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News Releases from Region 08

EPA reclassifies Denver area to “Serious” nonattainment for ozone

Reclassification requires additional control measures to reduce emissions

Contact Information: 
Richard Mylott (

DENVER—The U.S. Environmental Protection Agency (EPA) today announced the agency is finalizing a determination to reclassify the Denver Metro/North Front Range ozone nonattainment area from Moderate to Serious nonattainment under the Clean Air Act. 

“EPA is taking this action based on monitoring data showing that ozone remains a challenge in Denver and northern Front Range communities,” said EPA Regional Administrator Gregory Sopkin. “We thank our partners at the State of Colorado in working with EPA to strengthen air quality plans and implement these measures to further reduce ozone-forming emissions from sources across the region.”

The Denver area has been classified as a Moderate nonattainment area for the 2008 ozone 8-hour National Ambient Air Quality Standard since 2016. Based on an evaluation of air quality data collected from 2015 to 2017, EPA has determined that the Denver Metro/Northern Front Range nonattainment area did not meet the standard within the timeframe established for 2008 Moderate ozone nonattainment areas. Under the Clean Air Act, areas that do not attain national ozone standards in a timely manner are reclassified to a higher nonattainment status, in this case from Moderate to Serious.

Under the Clean Air Act, the State of Colorado is responsible for developing a State Implementation Plan (SIP) for ozone, a set of enforceable rules and programs to achieve compliance with national air quality standards. EPA’s action to reclassify the Denver area requires the State to revise its SIP in order to attain the ozone standard, and adopt new categories of controls, or reasonably available control technologies, on emissions sources.  Today’s action will also require the state’s permitting program to apply a lower threshold for permitting large sources. EPA’s action includes due dates for Colorado to submit SIP revisions and sets a new deadline of July 20, 2021, for the area to attain the 2008 ozone standard.

EPA accepted public comment on a proposal to reclassify the Denver Metro/Northern Front Range nonattainment area to serious nonattainment beginning on August 15 and held a public hearing at the agency’s regional office in Denver on September 6.

For details on EPA’s action, visit:

For a map of the Denver Metro/North Front Range nonattainment area, visit: