Ozone (2015 8-Hour Standard)

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).

Based on 2018 – 2020 ozone monitoring data the area failed to attain the 2015 Standard by the Marginal area attainment date and, as such, on October 7, 2022 the EPA finalized the reclassification of the DM/NFR nonattainment area to Moderate under the 2015 Standard with an attainment date of August 3, 2024.

On June 8, 2024, the State of Colorado requested that EPA reclassify the DM/NFR area to Serious based on a determination that the area would most likely not meet its attainment date, proactively seeking more time to adopt additional control measures and come into attainment. The EPA approved this voluntary reclassification to Serious on July 24, 2024.

In late March 2025, the State notified the RAQC Board of their intent to request EPA further reclassify the region as a “Severe” nonattainment area under this standard.