Air Quality in Denver, Colorado — Live
Live readings from PurpleAir sensors across Denver — with free alerts the moment the air turns.
Live Denver AQI from nearby PurpleAir sensors loads when this page opens in a browser, along with a live sensor map covering Denver and Aurora, Lakewood, Commerce City, Thornton, Arvada.
Denver has two air problems and they run on opposite calendars. The summer one is ozone, and it is bad enough that EPA's Green Book still listed the Denver-Boulder-Greeley-Fort Collins-Loveland area as a Severe nonattainment area for the 2008 ozone standard as of 30 June 2026, and the Denver Metro/North Front Range area as Serious for the newer 2015 standard. The winter one is the brown cloud — the visible haze that settles over the city when cold air gets pinned under warmer air. Ozone does not show up on a particle sensor at all, which is part of why a clear-looking Denver afternoon can still be a day to move your run indoors.
Canairy watches the sensors around your home, your kids' school, and everywhere else you care about, and tells you in plain English when the air changes enough to matter.
Front Range ozone, and where it actually comes from
The big field campaign that settled the argument was FRAPPÉ, run across the northern Front Range in summer 2014 by NCAR and its partners. Its finding was that motor vehicles and oil and gas operations are the two dominant local sources on days that break the health standard, each accounting for somewhere around 30 to 40 percent of local ozone production. The split is geographic: cars and trucks dominate through the Denver urban corridor up to Boulder, while oil and gas operations take over from Boulder north toward Fort Collins. Researchers also put Denver's background ozone — the part blown in from outside the region entirely — at 40 to 50 parts per billion, against a federal standard of 70 ppb averaged over eight hours. That is a narrow margin to work with, and it is why cutting local emissions by enough to shave 6 to 10 ppb matters so much here.
The oil and gas piece is the Denver-Julesburg Basin, northeast of the city. A study of two northern Front Range sites found that transport from upwind areas with heavy oil and gas activity accounted for roughly 65 percent of hourly elevated ozone episodes, against about 9 percent traced to the Denver metro area itself, and that about 88 percent of those elevated ozone events happened in June, July and August. Ozone Action Day alerts follow that pattern closely — one was in effect for the Front Range Urban Corridor, from Douglas County north to Larimer and Weld, on 27 July 2026, with the day's highest ozone reading at AQI 112.
The brown cloud is a winter thing
Winter visibility problems over Denver have been studied since the 1960s. The Regional Air Quality Council describes the brown cloud as an accumulation of carbon-containing particles smaller than 10 microns plus the chemical reactions of nitrogen oxides, ammonia and sulfur dioxide, which together block light and cut visibility. It is worse in winter because that is when temperature inversions trap cold air near the ground and stop the mixing that would otherwise disperse everything. The cloud was at its worst in the 1970s and 1980s and is much thinner now, but it has not gone away — the Denver AQI hit 154 on 6 March 2019, the highest March reading since 1983, and an Action Day for Visibility followed four days later.
Altitude works against the city in both seasons. Denver's official elevation is exactly one mile, 5,280 feet, with ground across the city ranging from about 5,130 to 5,690 feet. The abundant sunshine that comes with sitting high and dry drives the photochemistry that makes ozone in summer, and the same mile-high thin, cold, stagnant air lets pollution build up in winter.
The refinery in Commerce City
Denver's northern neighbour hosts Colorado's only refinery, and it has a long enforcement record. In February 2024 Suncor agreed to pay $10.5 million to settle a case brought by the Colorado Department of Public Health and Environment over emissions events between 2019 and 2021 — the largest air pollution settlement in state history. The settlement required Suncor to double its fenceline air quality monitoring and fix the operations behind excess releases of sulfur dioxide, carbon monoxide, nitrogen oxides and hydrogen sulfide, along with opacity and visible-emissions violations. Roughly $1.3 million was directed to projects in disproportionately impacted communities.
That was not the end of it. In July 2024 EPA issued its first notice of violation to the facility, citing Clean Air Act standards for benzene waste and hazardous air pollutants along with Title V permit violations; the plant had already drawn three state compliance advisories since 2021. If you live in Commerce City, Globeville, Elyria-Swansea or north Denver generally, it is worth knowing that benzene and hydrogen sulfide are not what a PurpleAir sensor measures. The sensors on this page are a good guide to smoke and general particle conditions, not to refinery-specific toxics.
Denver air quality FAQ
Why is there smoke in Denver today?
Most often it is wildfire smoke carried in from fires to the west and north, sometimes from hundreds or thousands of miles away, and in summer it stacks on top of an ozone problem that is already there. Through July 2026 the Front Range saw repeated Ozone Action Day alerts driven by heat and vehicle emissions, with wildfire smoke lifting particle pollution at the same time. In winter, haze over the city is more likely to be the brown cloud — an inversion holding traffic exhaust and other emissions near the ground rather than fire smoke.
What is the air quality in Denver right now?
This page shows the current AQI for Denver from PurpleAir sensors across the metro, updated continuously. One thing worth knowing: these sensors measure fine particles, so they will catch smoke and the brown cloud but not ozone, which is Denver's biggest regulated problem and is invisible. On a hot, still, sunny afternoon it is worth checking the state's Ozone Action Day alerts as well as the number on this page. The map below shows every live sensor so you can find the one nearest you.
Why does Denver keep failing the federal ozone standard?
Because the margin is thin and the sources are spread out. Background ozone drifting into the region already runs 40 to 50 parts per billion against a 70 ppb standard, so local emissions only have to add 20 to 30 ppb to break it. Research from the FRAPPÉ campaign found motor vehicles and oil and gas operations each contributing roughly 30 to 40 percent of local ozone production on exceedance days. As of 30 June 2026 EPA still classified the Denver area as Severe nonattainment for the 2008 ozone standard and Serious for the 2015 standard.
When is Denver's air usually at its worst?
Two windows, for two different pollutants. Summer afternoons — roughly June through August, when about 88 percent of elevated ozone events occur — bring ozone, driven by strong high-altitude sunshine acting on traffic and oil and gas emissions, and increasingly wildfire smoke as well. Then cold, still winter days bring the brown cloud, when an inversion holds particles and the gases that form them close to the ground.
What AQI level is unhealthy?
Under the US EPA scale, AQI 0–50 is Good and 51–100 is Moderate. From 101 the air is Unhealthy for Sensitive Groups — kids, older adults, and people with asthma or heart conditions — and above 150 it's Unhealthy for everyone. Canairy translates these numbers into a plain-English verdict, like whether to close the windows or move a workout indoors.
Is Canairy free?
Yes. The Canairy app is free to download and includes live air quality for all your saved places, plain-English verdicts, and free push alerts when the air crosses your threshold. A paid plan adds extras like SMS text alerts.
Get Canairy free on Google Play.