Madison, WI Air Quality Index (AQI) Today

That color and that number are today’s read on Madison air quality. Decide by the color first, the number second. The actual question underneath it is smaller: the isthmus bike path, soccer practice, whether tonight’s windows stay open. This page tracks the air quality Madison has actually breathed over the past month, not just the single figure sitting above. Set your own number and a text arrives when a plume pushes past it.

Madison’s typical month vs. its worst one

Search interest for “air quality madison” averages 9,900 a month across the trailing year. But the typical month runs only 720. One month, July 2026, spiked to 90,500 — the same Canadian smoke plume that pushed Chicago’s own AirNow reading from 597 to 742 AQI between mid-afternoon and late evening on July 16. That’s a 13.8x gap between the average and the typical month, close to Milwaukee’s 15.1x. Both are driven by a wildfire-season flood, not a steady year-round baseline. This page rebuilds the air quality Madison actually breathed over the past 30 days, from the same hourly feed as the reading above. It also carries a running count of days above AQI 100 in the last 12 months — the shape IQAir, AccuWeather and Wisconsin’s own monitor grid never show, because none of them track more than today’s single number.

Why is it hazy in Madison today?

Madison sits on a flat isthmus between two lakes, with none of the mountain walls that trap smog in a basin city. Most days the wind clears the air straight through. The exception is a Canadian wildfire plume, which ignores topography and can blanket the whole Upper Midwest corridor at once. Three things can also make the sky look worse than the reading: 24-hour averaging, smoke sitting aloft, or a distant station.

Wisconsin sits in the Upper Midwest lake corridor alongside Chicago, Milwaukee and Minneapolis. The AQI’s 24-hour average dilutes a bad afternoon across the day’s twenty calmer hours; smoke from a distant fire can sit aloft, thousands of feet up, above the monitor doing the measuring; or the nearest working station sits miles from wherever you actually are in the metro. None of that makes a hazy sky fake, or a clear one trustworthy — one number averages one location, not your block. A drifting plume and a number that lags it goes through the general case.

Eleven quiet months, then a flood. 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 Madison?

Two mechanisms trade off through a Madison year. Ground-level ozone builds on hot, still summer afternoons, invisible and odorless. PM2.5 dominates the rest of the year, from traffic and wood smoke. A Canadian wildfire plume can override both readings within hours. That’s the wildcard behind Madison’s own 13.8x average-to-typical-month gap, where a single smoke week can outweigh eleven ordinary ones.

The FAQ below carries today’s live read on which pollutant is actually driving the number.

Is the air safe to breathe in Madison today?

Madison sits on a flat isthmus between two lakes, where wind usually clears the air within a day. The exception is a Canadian wildfire plume, which ignores flat terrain and can blanket the whole Upper Midwest corridor at once. Go on a normal reading. Short and unloaded: mowing half the lawn instead of the whole yard. Don’t go once a plume pushes the color past 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. Past roughly 200, flat terrain or not, the plan moves indoors.

What AQI should you stay inside?

Wisconsin sets no air-quality threshold for schools or daycares — a structural gap, not an oversight. Licensing regulations require outdoor time and never mention air quality, so a provider that keeps the outdoor schedule during smoke isn’t violating any rule.

One commenter worked in Wisconsin schools and daycares for close to a decade. On r/toddlers, they laid out the mechanic: “I don’t think there’s anything in the state licensing regulations about air quality. However, the licensing regulations are very clear about children being given outside time.” A provider that keeps to the outdoor-time mandate, they added, “can’t be accused of a licensing violation” — air quality never enters the paperwork.

Minnesota, one state over, draws a real line: a parent there put it at 100, “because children are sensitive groups.” Washington locks a daycare cutoff at 80. Wisconsin has neither. Wisconsin’s licensing rule, and what it stops short of saying covers all three.

Adults here set their own numbers too, and they don’t agree with each other. On r/Marathon_Training, one runner wrote: “I’ll run in up to 110 because…error bars.” One asthmatic runner logged 156 runs against AQI and set a cutoff at 60. Past it, “my lungs struggle regardless of how well I’ve trained,” even though EPA calls nothing under 100 unhealthy. That log: 87% of runs under AQI 50 went fine, 42% between 50 and 70, just 12% above 70. Wildfire smoke — the same Canadian plume that overrides Madison’s usually-clearing wind — pulls that whole table down roughly one EPA band.

Indoors, default to a portable HEPA purifier or a Corsi-Rosenthal box. One builder priced a 12x14 bedroom’s worth at around $130. Skip the whole-house MERV-13 swap unless a licensed tech has checked the system’s static pressure first. What a Corsi-Rosenthal box does that a filter swap doesn’t has the detail.

EPA AirNow’s own colours and breakpoints. The three marked cutoffs are not EPA guidance and not Madison 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 both directions here, and the second one catches people off guard. A clear sky with a bad number is usually ground-level ozone, Madison’s dominant summer pollutant. It’s invisible and odorless, with no way to smell a safe read. A hazy-looking sky with a calm official number is usually 24-hour averaging, or smoke sitting aloft above the monitor.

Neither direction means the number is wrong. It means the number and your senses are reading different things.

That’s the station behind today’s reading — its distance from downtown Madison, and the nearby PurpleAir sensor count. A station miles off under-reports whichever side of the metro sits farthest from it. What sits behind this number, and where it gets thin is set out plainly.

FAQ

What’s the air quality forecast for Madison tomorrow?

Wind direction and any incoming plume can shift this within hours. Treat it as a direction, not a lock — recheck the morning of.

What’s the UV index in Madison today?

UV runs on its own scale, separate from AQI. A clear, low-AQI day can still be the highest-UV day of the week, so a good air quality reading isn't a reason to skip sunscreen.

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

See how Madison ranks today against every tracked city. Its rank moves hardest during wildfire season, when the Canadian plume corridor is active.

What is in the air in Madison right now?

That's today's specific reading. Ground-level ozone typically dominates summer afternoons here; PM2.5 from traffic, wood smoke or an active wildfire plume dominates the rest of the year.

Why does it smell like smoke outside in Madison?

Wildfire smoke is burning vegetation, usually carried in from Canada along the same corridor that reaches Chicago and Minneapolis. It’s a different particulate mix from ordinary traffic exhaust at the same AQI number. If a plume is active, Which metros are under smoke right now tracks the plume itself.