An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

News Releases

News Releases from Region 08

EPA proposes to reclassify Denver area to “Serious” non-attainment for ozone

Reclassification from Moderate to Serious requires additional control measures to reduce emissions

Contact Information: 
Richard Mylott (

DENVER—The U.S. Environmental Protection Agency (EPA) is proposing to determine that the Denver Metro/North Front Range ozone non-attainment area did not meet the 2008 National Ambient Air Quality Standard (NAAQS) by the specified deadline and should be reclassified from a Moderate to a Serious non-attainment area. EPA will be accepting public comment on the proposed action for a 30-day period beginning on August 15 and will hold a public hearing at the Agency’s regional office in Denver on September 6.

“EPA is proposing this action as required by the Clean Air Act,” said EPA Regional Administrator Gregory Sopkin. “We will continue to support the State as they revise plans and implement new measures that will reduce ozone-forming emissions across the many sources contributing to air quality impairment along Colorado’s Front Range.”

The Denver area has been classified as a Moderate non-attainment area for the 2008 ozone 8-hour NAAQS since 2016. Based on an evaluation of air quality data collected from 2015 to 2017, the Agency is proposing to determine that the Denver Metro/Northern Front Range non-attainment area did not meet the standard within the timeframe established for 2008 Moderate ozone non-attainment areas. Under the Clean Air Act, areas that do not attain national standards in a timely manner are reclassified to a higher non-attainment 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), which is a set of enforceable rules and programs to achieve compliance with national air quality standards. EPA’s action proposes due dates for Colorado to submit SIP revisions to attain the ozone standard, including the implementation of reasonably available control technologies.  Some Serious area requirements would be effective as soon as this action is finalized, such as a lower threshold for permitting large sources. The proposal would set a new deadline of July 20, 2021, for the Denver area to attain the 2008 ozone standard.

For details on EPA’s proposed action, the September 6 public hearing, and information on how to comment, visit:

For a map of the Denver Metro/North Front Range non-attainment area, visit: