Colorado has issued Action Day alerts on consecutive days this week for both ozone and fine particulates along the Front Range, and the guidance attached to them contains a request that has drawn skepticism from residents watching smoke roll in from fires hundreds of miles away.
The state advisory tells residents that even during periods of wildfire smoke, reducing personal emissions can help decrease ozone production. The alerts were issued by the Colorado Department of Public Health and Environment together with the Regional Air Quality Council, covering the Front Range Urban Corridor from Douglas County north to Larimer and Weld counties, including the Denver-Boulder area, Fort Collins and Greeley. The current alert runs until at least 4 p.m. Thursday.
The skepticism is understandable. If the haze came from somewhere else, why does driving less in Denver matter? The answer turns on the difference between the two pollutants in the same alert.
Two Pollutants, Two Different Origins
Smoke and ozone are not the same thing, and conflating them is what makes the state's message sound contradictory.
Fine particulate matter, or PM2.5, is the visible component. During this event, it is largely transported, arriving with smoke from regional fires, and there is little a Denver household can do to reduce the amount arriving overhead.
Ground-level ozone is not emitted directly by anything. It forms through chemical reactions between nitrogen oxides and volatile organic compounds in the presence of sunlight and heat. CDPHE identifies vehicles that run on gas, other equipment running on gas or fossil fuels, and industry operations as the large sources of those precursors in Colorado. Wildfire smoke contributes precursors as well, and its particles and gases interact with the same chemistry.
That is the basis of the state's claim. Reducing local precursor emissions on a hot, sunny day reduces the amount of ozone formed locally, and that holds whether or not smoke is also present. The advisory's specific wording is that reducing personal emissions can help decrease ozone production, which is a modest and defensible statement rather than a claim that individual action solves the problem.
The Front Range Has a Structural Ozone Problem Independent of Fires
The regional context is what gives the message weight, and it long predates this week's smoke.
The Denver Metro and North Front Range region is designated nonattainment for federal ozone standards, meaning it does not meet them. EPA reclassified the area from serious to severe under the 2008 standard in 2022, and in July 2024 approved the state's voluntary request to move from moderate to serious under the 2015 standard. The Regional Air Quality Council serves as the lead air quality planning organization for a nine-county nonattainment region.
Last year briefly looked like progress. RAQC reported that monitors recorded 23 days above the federal ozone standard in 2025, which the council described as the lowest ozone season since 2009 and attributed largely to favorable weather. CDPHE called 33 Ozone Action Day alerts that year. RAQC executive director Mike Silverstein credited the improvement primarily to cooler, more turbulent conditions rather than to emissions reductions.
This year has erased that margin. Front Range monitors have already recorded 51 days above the EPA cap of 70 parts per billion with weeks remaining in the ozone season, and Silverstein has said the region now appears unlikely to meet the three-year average even after allowances for out-of-state wildfire smoke, raising the prospect of fresh federal sanctions.
That is the honest answer to the fairness question. Smoke did not create the Front Range ozone problem, and a single good weather year did not fix it.
The Alerts Ask for Two Different Things at Once
There is a genuine tension inside a multiple pollutants alert, and residents deserve to have it named.
The ozone guidance asks people to reduce driving of gas and diesel vehicles, delay refueling until evening, avoid gas-powered lawn equipment, and limit idling, all of which cut precursor emissions during peak formation hours. The particulate guidance asks people to reduce exposure by staying indoors.
Those are compatible, and in fact reinforcing, because both point toward spending less time in a car and outdoors during the hottest part of the day. Where they diverge is exertion. Ozone alerts advise avoiding rigorous outdoor activity during the heat of the day, while smoke guidance generally advises limiting outdoor exertion.
Nothing in the state's messaging asks households to substitute personal action for regulation. RAQC develops emission control strategy options through State Implementation Plans, and the individual guidance runs alongside that rather than instead of it.
The Health Guidance Is the Part That Should Not Get Lost
Whatever a reader concludes about policy messaging, the exposure advice is straightforward and worth following.
The state advisory notes that ozone exposure can cause acute respiratory problems and trigger asthma attacks, and that prolonged exposure can cause long-lasting damage to the lungs. This week's alerts forecast ozone in the moderate to unhealthy for sensitive groups range, with the highest concentrations most likely in the southern and western portions of the Denver metro area. Particulate readings reached the unhealthy for sensitive groups category at some monitors earlier in the week, a level at which people with heart or lung disease, older adults, and children should reduce prolonged or heavy exertion.
The groups that should act first are people with asthma or COPD, people with heart disease, pregnant people, infants and young children, adults over 65, and anyone who works or exercises outdoors. Asthma and COPD patients should keep rescue inhalers accessible and confirm with a clinician when to step up controller medication. Do not change any prescribed medication without speaking to a clinician.
Chest pain, severe shortness of breath, wheezing that does not respond to a rescue inhaler, palpitations, or confusion require urgent evaluation.
Action Day alerts are issued in advance based on forecast conditions, and ozone does not always exceed the standard on alert days. Current conditions and forecasts are posted on the state air quality site. MedicalDaily will continue tracking Front Range alerts and the state's ozone attainment progress.
Frequently Asked Questions
What is an Action Day Alert? A forecast-based advisory from CDPHE and the Regional Air Quality Council warning that pollution is expected to reach unhealthy levels and asking residents to reduce emissions.
Why cut emissions if the smoke came from elsewhere? Smoke is particulate matter. Ozone forms locally from vehicle, industrial, and other precursor emissions reacting in sunlight, and reducing those still lowers ozone.
Does individual action actually matter? The state's claim is that it helps, not that it solves the problem. Controls on major sources are handled through State Implementation Plans.
Is the Front Range in compliance with ozone standards? No. The nine-county Denver Metro and North Front Range region is designated nonattainment under both the 2008 and 2015 federal standards.
How bad is this year? Front Range monitors have already logged 51 days above the federal ozone cap, with weeks left in the season, compared with 23 days in all of 2025.
What should I do on an Action Day? Avoid rigorous outdoor activity during the heat of the day, reduce driving and idling, delay refueling until evening, and skip gas-powered lawn equipment.
Who is most at risk? People with asthma, COPD or heart disease, pregnant people, infants, young children, adults over 65, and outdoor workers.
