Fort Collins, CO Air Quality Index (AQI) Today

Fort Collins gets its own reading up there. It isn’t a number borrowed from Denver, 65 miles south. The air quality Fort Collins breathes runs on its own two-season calendar, covered below. The color decides something specific — the Horsetooth trail run, the CSU tailgate, whether tonight’s the night the windows stay open. This page tracks what Fort Collins itself has breathed over the past 30 days, not just the figure sitting above. Pick your own threshold and let the alert do the refreshing.

Fort Collins’s last 30 days, not just today

A single number can’t say whether today is a blip or the start of a run of bad days. This chart rebuilds the air quality Fort Collins has actually seen over the trailing 30 days. It pulls from the same hourly AQI feed as the number above. A running count tracks days above AQI 100 in the last 12 months. IQAir, AccuWeather, aqicn and Colorado’s own monitor grid all stop at today’s figure. None of them render the shape behind it. Up here, shape matters more than in most cities on this list. Fort Collins runs on two separate calendars — a wintertime particulate stretch (PM2.5 and PM10 both) and a summer ozone stretch. They don’t look anything alike side by side.

Why is it hazy in Fort Collins today?

Three explanations cover most hazy-but-moderate days. A 24-hour average can smooth out one rough hour. Smoke can sit aloft above the monitor, or a station can stand in for a stretch of city it isn’t next to. Fort Collins adds a fourth, regional one. Colorado’s Regional Air Quality Council issues a single Front Range Ozone Action Day alert covering the whole corridor at once, not city by city.

That corridor covers Fort Collins, Denver and Colorado Springs at once, and the ozone driving it doesn’t stop at a city limit either. shows whether one is in effect right now. None of that makes a hazy sky here fake. It means the reading is one average, from one station, standing in for a corridor running more than 100 miles north to south. Winter particulate, summer ozone, and the gap between them covers the general case.

Two equal peaks, eleven months apart. Search volumes, not AQI readings — bars are neutral blue-grey with the peak month in accent blue, never EPA band colours, so demand data can never be read as a measurement of the air.

What is causing the bad air in Fort Collins?

The same number gets worn by winter and by summer here, on two different calendars, and neither one starts in Fort Collins. Winter’s version drifts up from the brown cloud, Denver’s decades-old nickname for its own wintertime haze. Cold air traps vehicle and industrial emissions along the length of the Front Range. Summer’s version, ground-level ozone, matters more up here, cooked from vehicle exhaust and Denver-Julesburg Basin oil-and-gas emissions.

That ozone can form well south of the city and drift north on an ordinary afternoon wind, before Fort Collins ever measures it. No Fort Collins-specific community thread describing either mechanism turned up in the material reviewed. The corpus for this city is thinner than for Denver or Colorado Springs — a gap worth stating rather than papered over with borrowed detail. Denver’s own residents describe the brown cloud and the ozone in more first-hand detail than this page can for Fort Collins specifically.

Is the air safe to breathe in Fort Collins today?

A single Front Range Ozone Action Day can cover Fort Collins, Denver and Colorado Springs at once. It’s issued for the whole corridor, not any one city. It can run a step ahead of, or behind, what Fort Collins is reading right now, so check the local number first. Go on a normal reading. Short and unloaded: the short bike commute instead of the group ride out toward Horsetooth.

Don’t go once the number climbs into the red. EPA opens its everyone-warning at 151, Unhealthy. It treats 201 to 300, Very Unhealthy, as that same warning at a more serious stage — not a separate group. Above roughly 200, the corridor alert and the local reading agree on one thing: stay in.

What AQI should you stay inside?

Nothing turned up for a Colorado school or daycare AQI rule in the material this project has reviewed. Washington and Minnesota remain the only two documented exceptions. Which states put a number in writing has what’s confirmed.

The Front Range’s shared Ozone Action Day alert says nothing about where an individual’s own threshold sits. That’s a personal number, and it runs well under the EPA’s single sensitive-groups line. “I’ll run in up to 110 because…error bars,” a runner on r/Marathon_Training wrote, naming their own ceiling. An asthmatic runner logged 156 runs against AQI instead and set a lower one, 60. Past it, “my lungs struggle regardless of how well I’ve trained,” despite EPA calling nothing under 100 unhealthy. Their log: 87% of runs under 50 went fine, 42% between 50 and 70, just 12% past 70. Parents online land closer to 100.

Wildfire smoke pulls that whole table down further still, roughly one EPA band, layered on top of whatever the ozone corridor is already doing. EPA’s own name for that stretch is 101–150, Unhealthy for Sensitive Groups — attributed, and not aimed at any one reader. Indoors, default to a portable HEPA purifier or a Corsi-Rosenthal box; one builder priced a 12x14 bedroom’s worth at $130. Skip the whole-house MERV-13 swap unless a licensed tech has checked the system’s static pressure first. Monitor first, purifier second, filter third explains why.

EPA AirNow’s own colours and breakpoints. The three marked cutoffs are not EPA guidance and not Fort Collins rules — each is one reader’s or one institution’s own line.

Why our number may not match what you are seeing and smelling

The mismatch runs in two directions here, and the second one is the harder sell. A hazy sky with a moderate number is usually the 24-hour average, or a station standing in for the wrong stretch of the corridor. A clear, still summer afternoon can look like the best day of the week and still carry a triple-digit reading. Ground-level ozone is invisible and odorless.

There’s no smelling your way to a safe read on it. Fort Collins sits at the north end of a corridor built around that exact mismatch. It’s the whole reason the region issues one shared ozone alert instead of 28 separate ones. shows the station behind today’s number, its distance from the city center, and the nearby PurpleAir sensor count. A station standing in for a smaller city like this one carries a wider margin than one covering a dense urban core. Why a smaller city’s station carries a wider margin explains the arithmetic.

Fort Collins shares a corridor, not a copy

Search interest here tracks the same two-season pattern as the 30-day history: a winter particulate stretch, then a summer ozone stretch, not one clean peak. What makes Fort Collins different from its Front Range neighbors isn’t the mechanism — it’s the distance.

Denver carries the region’s brown-cloud history and its own ozone-source detail. Colorado Springs sits under the same alert system, from the south end of the corridor. Fort Collins is the north end of the same airshed. It’s genuinely thinner on its own first-hand community record, and that gap is stated here rather than papered over with borrowed detail.

FAQ

What’s the air quality forecast for Fort Collins tomorrow?

Ozone and inversion conditions can both shift within a day, especially near a Front Range Ozone Action Day. Treat it as a direction, not a lock, and recheck the morning of.

What’s the UV index in Fort Collins today?

UV runs on its own scale, separate from AQI. A clear, low-AQI day at this elevation is often the highest-UV day of the week. A good air quality reading isn't a reason to skip sunscreen.

Who has the worst air quality in the US right now?

Fort Collins’s readings move hardest during summer ozone season, and whenever the region’s Front Range alert is active. See today’s live ranking of all 28 metros for where this one lands.

What is in the air in Fort Collins right now?

That's today's specific reading. Ground-level ozone tends to dominate summer afternoons here; fine particulate matter (PM2.5) drifting up from the wider Front Range dominates winter.

What AQI should you not exercise in?

There’s no single number — it depends on who’s asking and how long they’re out. Runners in the community cite up to 110. Parents cut outdoor time around 100. One asthmatic runner’s own 156-run log put their cutoff at 60. Wildfire smoke pushes all of those down roughly one EPA band.

Why does it smell like smoke outside in Fort Collins?

Wildfire smoke is burning vegetation, often carried in from well outside the state. If a specific fire is active, Where the smoke came from and how long it stays picks it up. It differs from an ordinary ozone or brown-cloud day.