Record high temperatures and relatively stagnant air on the northern Front Range are pushing monitors for health-damaging ozone well past violations, and the accumulation of high readings ensure Colorado will fail a three-year averaging test to bring the choking gas below federal limits, local air quality officials said.
The 10 Front Range counties making up the ozone nonattainment area have already recorded 51 days above the Environmental Protection Agency cap of 70 parts per billion, with weeks left to go in the ozone danger season. Thirty-four of those days even spiked above the older, more lenient cap of 75 parts per billion. That compares with 23 total days above 70 ppb last year, when favorable winds and relatively cooler temperatures gave regional air officials some hope the counties could string together a couple of years attaining the limits.
Under the U.S. Clean Air Act, if the EPA determines Colorado has not made progress toward the ozone limits in averages taken from 2024 through 2026, the federal government can impose new sanctions. That could include expanding the number of industrial sources that need an air pollution permit, or restrictions on volatile paints and household cleaners and solvents that give off ozone precursors.
Even after allowances for out-of-state wildfire smoke Colorado can’t control, “now it appears that we can’t make it” for the three-year average, said Mike Silverstein, executive director of the Regional Air Quality Council, which makes policy recommendations to state and local regulators.
“We got some hope in 2025 that the strategy package that we had in place was going to really hit the mark,” Silverstein said, including programs to switch out highly polluting lawn and garden machinery with clean electric motors. “Our modeling from a couple years back indicated that we would be close, and that we had an opportunity to attain by 2026, but the data isn’t bearing that out.
“It’s obvious more work needs to be done, and emissions are simply too high in our regions for us to sustain or to achieve good air quality,” Silverstein said.
Wildfire smoke drifting in from intense Washington state and Oregon crises are forecast to make Front Range air quality worse over the next few days.
The accumulation of bad readings comes at the same time a study lands from the Colorado School of Public Health detailing for the first time the hundreds of deaths and thousands of serious illnesses caused by the 10 counties’ high ozone days. Ozone causes lung and other tissue inflammation, asthma attacks and other respiratory distress, hitting particularly hard at children and older adults with chronic obstructive pulmonary disease.
The School of Public Health study says that over the five years ending in 2024, the northern Front Range nonattainment area experienced 223 days above the 70 ppb standard that the EPA set in 2015. If the counties had instead met those limits in that time, it would have prevented 170 deaths, 390 respiratory hospitalizations, 120 asthma-related ER visits, and more than 35,000 school days missed from asthma, the authors say.
The societal cost of those excess, ozone-related deaths and health problems was estimated between $211 million and $580 million each year in 2024 dollars, the study says.
If ozone levels average 10 ppb higher than current observed measurements in coming years, 70 ppb standard during that time — and monitoring shows they did reach that high on some days — the Front Range could see 570 excess deaths, 1,310 excess respiratory hospitalizations, and nearly 120,000 missed days of school due to asthma. The cost of that rise in ozone would be between $712 million and $1.9 billion a year.
The Regional Air Quality Council asked for a study of ozone’s real-world impacts, Silverstein said, but did not direct what the researchers chose to illustrate the problem.
“It’s obvious by our data that we need to do even more, and that this study now provides us the evidence that we need to justify why more needs to happen,” Silverstein said. “It’s not just a number that the monitors read. It has implications for the public health of our community.”
Study co-author Sheryl Magzamen, a Colorado State University epidemiology professor and School of Public Health researcher, said the report can help put human scale to decades of ozone battles in Colorado.
“Health needs to be — I’m not only saying this as a public health person, but a current resident of the nonattainment area — health needs to be part of the conversation when we’re talking about ozone policy,” Magzamen said.
Ozone on the Front Range builds up when volatile organic compounds from oil and gas production and gasoline fumes combine with nitrogen oxides from burning fossil fuels in power plants and vehicle engines. They cook in sunlight and high heat, and are made worse with the addition of wildfire smoke.
The current nonattainment area includes Douglas, Arapahoe, Denver, Jefferson, Broomfield, Boulder, Adams, Weld and part of Larimer County.
This summer’s readings show Colorado’s ozone problem is spreading beyond the traditional northern Front Range counties, said Jeremy Nichols, with the Center for Biological Diversity. Monitors in Gilpin and El Paso counties “both have three-year averages so far that are above the national ambient air quality standards.
“What this increasingly confirms is that ozone is impacting a much larger contiguous region along the Front Range, potentially stretching from Pueblo County north to all of Larimer and Weld Counties, west to the high country of Gilpin and likely Clear Creek counties,” Nichols said.
The state health department’s Air Pollution Control Division could speed up mandatory mitigation measures by asking the EPA for an early declaration of “extreme” ozone violation status, the next downgrade from “severe,” Nichols said. That would also move up the deadlines for the state Air Quality Control Commission to approve policy measures for a plan that meets the attainment limits.
“If the Polis administration sees the writing on the wall now, they should do something about it,” Nichols said.