The Front Range recorded its lowest ozone levels in 16 years this summer, but the region still needs to reduce air pollution to escape federal oversight that requires more stringent permitting for polluting industries and more expensive gasoline for drivers.
The nine-county region recorded 23 days between late May and early September when ozone pollution levels exceeded federal air quality standards, mostly because weather conditions prevented the stagnant heat that creates the ground-level ozone that forms hazy smog.
In 2024, the region recorded 41 days in which pollution levels rose above federal standards, according to data released Thursday by the Regional Air Quality Council.
This summer was the lowest ozone season for the region since 2009, according to the data.
“The region experienced much better air quality,” said Mike Silverstein, executive director of the air quality council. “The continuing saga we’re still faced with is we still have too many bad ozone days.”
The summer ozone season stretches from mid-May to early September when the bright sun’s ultraviolet rays bake volatile organic compounds and nitrogen oxides into a haze that hovers and holds heat over the Front Range. The pollution is harmful to people, especially children with asthma, the elderly and others with breathing conditions such as chronic obstructive pulmonary disease.
On days when meteorologists forecast weather conditions conducive to ozone formation, the Colorado Department of Public Health and Environment’s Air Quality Control Division issues alerts that warn residents and ask them to drive less and adopt other measures to reduce air pollution.
This summer, the division issued 33 alerts. Two of those alerts were issued in early May, which is earlier than usual. The last alert was Sept. 4.
Because there were more alerts than actual days where air pollution exceeded federal levels, Silverstein said it is likely that actions the state has taken to reduce air pollution are working.
“That gives us an indication that our pollution control programs seem to be having a contribution as well,” he said.
The region is failing to meet two air quality standards set by the Environmental Protection Agency.
The first benchmark is to lower the average ozone pollution to a 2008 standard of 75 parts per billion. The northern Front Range is in “severe non-attainment” for that number.
However, only six days exceeded that standard this summer, and no single monitor recorded more than three exceedances, meaning Colorado complied with that standard in 2025. It’s the first time the state has met that benchmark since 2017, according to Regional Air Quality Council data.
“So this year is what we call a clean data year,” Silverstein said.
However, that does not mean the EPA will lift restrictions on Denver. The state must maintain those levels on a three-year average and then sustain that average for decades. Since 2024 was not within the acceptable range, it is unlikely that a three-year average that includes summer 2026 will be within the target.
The second benchmark requires the region to lower its average ozone pollution to a 2015 standard of 70 parts per billion, considered the most acceptable level of air pollution for human health. Seventeen days in 2025 exceeded that standard, according to the data.
The state’s Air Pollution Control Division in April asked the EPA to downgrade its status to “severe non-attainment” of those 2015 standards. The state already has that designation for the 2008 standards.
When a state hits the severe non-attainment status, the federal government imposes tighter regulations, which are required under the Clean Air Act. Those regulations include a requirement that motorists in the Front Range use reformulated gas, a blend that burns cleaner but is more expensive, and to increase the number of businesses that must apply for permits to pollute the air.
Colorado will be under those restrictions for the foreseeable future, Silverstein said. So work toward cleaner air continues.
The council this summer launched a new air quality study with the state health department and Colorado State University to figure out how to build better models and ways to measure the pollutants in the air. It’s the first study of its kind since 2014.
Andrey Marsavin, who is working on his doctorate in atmospheric science, spent the summer with a team of graduate students riding around the Front Range in a Chevrolet Tahoe loaded with scientific instruments that suck air into canisters so they can research the levels of chemicals.
Marsavin said they are looking into the “big soup of chemistry” that makes up the ground-level ozone.
“A lot of complicated chemistry goes on behind this,” Marsavin said. “I’m researching how to untangle that and distill it into policy to bring ozone down.”
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