Denver ozone downgraded to 'severe' by EPA, but carbon monoxide levels are low

While the Denver Metro/North Front Range ozone non-attainment area was recently downgraded to “severe” by the Environmental Protection Agency, pretty much the entire Front Range — from Colorado Springs to Fort Collins — is on the cusp of escaping the eye of the EPA regarding outdoor carbon monoxide air pollution.

On Thursday, the Colorado Air Quality Control Commission voted to revise regulations imposed by EPA rule to acknowledge 20 years of compliance with federal standards.

The EPA designated the Denver metropolitan area as a "non-attainment" area for carbon monoxide in 1978, when CO levels exceeded the national air quality standards of 9 parts per million for an 8-hour average and 35 ppm for a 1-hour average.

Denver frequently exceeded the standards during the late 1970s and 1980s. The notorious “brown cloud” that suffocated the Denver Basin during the winter months when temperature inversions trapped pollutants close to the ground, caused CO levels nearly three times higher than allowed.

As a result of the EPA classification, state mitigation efforts were imposed, including vehicle emissions testing, cleaner fuels and the federal requirement for catalytic converters on vehicles in 1975.

By 2001, Denver achieved attainment and became a "maintenance area," meaning it met the federal CO standards but would continue to be monitored for 20 years to ensure ongoing compliance.

“The state of Colorado has effectively kept outdoor carbon monoxide pollution low for the past 20 years. It is now more than 80% below the U.S. EPA health-based standard,” according to a release from the Colorado Air Pollution Control division. “Colorado went above and beyond achieving the federal standard — the state has kept carbon monoxide levels more than 80% below EPA’s standard. Colorado has achieved and maintained carbon monoxide levels below 4.7 parts per million over 8-hour time periods for 20 years and reached levels below 0.8 parts per million.”

“This success story shows that Colorado can meet and even exceed federal air quality standards,” said Air Pollution Control Division Director Michael Ogletree in the release. “We achieved attainment for carbon monoxide, and we’re making headway to do it again for other air pollutants.”

“The air commission celebrates this success and was thrilled to approve these revisions to the state’s air quality plan,” said Commissioner Patrick Cummins, Chair of the Colorado Air Quality Control Commission.

“EPA must next review the maintenance plan revisions. Colorado will submit the revisions to EPA following the state’s 2025 legislative session,” said the release.