Denver’s air ranked worst in the United States on Monday, July 6, and at times sat among the world’s worst major cities, according to monitoring service IQ Air.
By 4 p.m. that afternoon, the Colorado Department of Public Health and Environment (CDPHE) and the Regional Air Quality Council issued an Ozone Action Day Alert. The alert covers the entire Front Range Urban Corridor, stretching from Douglas County north through Denver, Boulder, Fort Collins, and Greeley. It remains in effect through at least 4 p.m. Tuesday, July 7, 2026.
Two problems are stacking on top of each other. Wildfires burning in Colorado and Utah are pushing smoke across the state, and hot summer weather is cooking that pollution into ground-level ozone. Denver’s bowl-shaped geography traps both, so the haze builds up with nowhere to go.
A Busier Season Than Last Year
State air quality forecasters have issued 20 alerts for the Northern Front Range so far this summer, up from 13 at the same point last year. Another 22 smoke advisories have gone out for the rest of the state, and the current wildfire smoke advisory alone covers 22 counties, including Durango, Telluride, Aspen, Vail, and Breckenridge, through Wednesday morning.
Source: Colorado Air Quality Summary
The readings back up the warnings. Denver Metro’s air quality index peaked in the Unhealthy range on Monday. By Tuesday morning, the metro was back in Unhealthy for Sensitive Groups territory, Aspen registered an AQI of 117 from fine particle pollution, and forecasters expect similar conditions through midweek.
Who Feels It First
Wildfire smoke carries fine particles (PM2.5) small enough to slip past the body’s natural defenses and settle deep in the lungs. The particles travel hundreds of miles from the fire itself and affect health even when the smoke stays invisible and odorless.
Front Range hospitals and urgent care clinics are reporting more patients with:
- Shortness of breath
- Chest tightness
- Coughing
- Asthma flare-ups.
People with COPD, asthma, chronic bronchitis, or heart disease face the highest risk, along with older adults, children, pregnant women, and anyone who works or exercises outdoors.
How to Protect Yourself
CDPHE recommends a few practical steps while the alerts hold:
- Check current conditions at Colorado Air Quality or AirNow before heading outside
- Limit outdoor activity between noon and 8 p.m., when ozone peaks
- Keep windows and doors closed, and run air conditioning on recirculate
- Use a HEPA air cleaner in the room where you spend the most time
- Wear a well-fitting N95 or KN95 mask if you must be outdoors (cloth and surgical masks are too porous to stop smoke particles)
- Keep inhalers and respiratory prescriptions filled and within reach
If You Use Supplemental Oxygen
Stay on your prescribed schedule. Smoke exposure inflames the airways and can lower blood oxygen levels in people with chronic lung disease, so consistency with your therapy matters more than usual on poor air days.
Pay attention to how you feel, and call your doctor if your usual flow rate stops keeping up or if shortness of breath worsens. Severe symptoms such as chest pressure or significant difficulty breathing belong in the emergency room.
Your equipment deserves a quick check too. Inspect and clean your concentrator’s intake filter during extended smoke events, since dirtier air means the filter works harder.
Alpine Oxygen concentrators come standard with HEPA filtration, which captures fine particles like those found in wildfire smoke, so the air feeding your therapy stays clean even when the air outside is hazy.
Expect More Alerts This Summer
Forecasters expect shifting winds to carry some smoke out of the region, but the heat is staying put, and so are the fires. State meteorologists say alerts will likely continue through the summer. Sign up for CDPHE’s automated air quality emails, check the AQI each morning, and plan outdoor time for early in the day when ozone is lowest.
