Ozone (2008 8-Hour Standard)

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.

As a Moderate nonattainment area the DM/NFR had an attainment date of July 20, 2018. Attainment was to be demonstrated based on certified ozone monitoring data from calendar years 2015-2017. The area failed to meet the 2008 Standard during this time. The area did have one year of data below the standard and, as such, a 1 year extension was requested by Colorado in 2018. The request, however, was withdrawn by the State on March 26, 2019.

Following the revocation of the 1 year extension the area was reclassified to a Serious nonattainment area under the 2008 ozone Standard in December 2019. A Serious SIP was developed and approved by the AQCC in December of 2020, and was then submitted to the EPA in March 2021 following legislative approval.

Based on 2018 – 2020 ozone monitoring data the area failed to meet the 2008 Standard by the Serious area attainment date and, as such, on April 13, 2022 the EPA finalized the reclassification of the DM/NFR nonattainment area under the 2008 Standard to Severe with an attainment date of July 20, 2027.