Air Quality in Frederick, Maryland — Live
Live readings from PurpleAir sensors across Frederick — with free alerts when summer ozone turns the air unhealthy.
AQI 21 from 4 PurpleAir sensors · Trending up · data from PurpleAir
As of , the air quality in Frederick, Maryland is AQI 21 — Good and rising — with PM2.5 at 3.8 µg/m³, the median of 4 live PurpleAir sensors reading 3 to 32. Canairy's verdict: Breathe easy.
For scale, that PM2.5 reading is below the World Health Organization's 24-hour guideline of 15 µg/m³. The WHO figure is a daily average and this is a live reading, so read it as a sense of magnitude rather than a formal exceedance — a brief spike and a bad day are not the same thing. More on the WHO guidelines
Pollen today in Frederick: weeds pollen is the strongest of the three at a very high level, from Google's pollen forecast. Canairy shows the tree, grass and weed forecast beside the air reading on every plan, including the free one.
Free to download · Live data from PurpleAir & public monitors
Live PurpleAir sensor map for Frederick and Middletown, Urbana, Thurmont, Emmitsburg. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Frederick
The sensors Canairy reads in Frederick agree right now — all 4 sit in the Good band, a 29-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| 1.3 mi SW | 3 | Good |
| 1.4 mi SE | 21 | Good |
| 1.9 mi NNE | 21 | Good |
| 3.2 mi WSW | 32 | Good |
Frederick's air is usually fine — this is not a wildfire-smoke town. The reason to pay attention here is different: Frederick County sits inside the federal government's "moderate" ozone nonattainment area for the Washington, D.C. region, and on hot, still summer days the same smog that builds up over the capital rides up I-270 into the Monocacy Valley.
What Canairy does for Frederick
A clear verdict
Not just a number — a plain-English call for Frederick: open the windows, or keep them shut.
Smoke alerts
A push or text the moment the air crosses your threshold — and again when it clears.
A heads-up before it's bad
Trend alerts catch the air turning, so you can close up the house before the smoke settles in.
Every place you care about
Home, work, the kids' school — across Frederick or across the country, on one screen.
What the air in Frederick is doing next
| When | AQI | Expected air quality | Main pollutant |
|---|---|---|---|
| Today | 38 | Good | ozone |
| Tomorrow | 44 | Good | ozone |
| Thursday | 44 | Good | ozone |
A steady inflow of clean Canadian air is expected Tuesday as high pressure sits just north of the region. Expect both ozone and fine particulates to be comfortable in the Good AQI range. Winds turn southerly Wednesday, persisting into Thursday as high pressure shifts off the New England coast. An uptick in temperatures and dew points will lead to a slight increase in both ozone and fine particulates. However, given an initially clean residual air mass and late season sunlight duration, expect both to remain in the Good AQI range statewide. For the latest air quality information, please visit our website here. -MDE
Forecast from EPA AirNow for the Maryland Piedmont reporting area. Canairy watches the live sensors against it and tells you when the air actually crosses your threshold, rather than leaving you to check.
Frederick's real air problem is summer ozone, not smoke
The U.S. EPA's Green Book — the federal government's official ledger of places that don't yet meet national air quality standards — lists Frederick County as part of the Washington, D.C.-MD-VA moderate nonattainment area for ground-level ozone. That's a different kind of problem than the wildfire smoke that dominates air-quality conversations out West: ozone isn't smoke drifting in from somewhere else, it's a gas that cooks up locally when vehicle exhaust and other emissions sit in strong summer sunlight.
It forms worst on hot, sunny, calm afternoons from June through August, usually peaking in the mid-to-late afternoon after a morning of traffic and heat have had time to react. Those are also the days Washington and Baltimore's own ozone problems are at their worst, and Frederick sits close enough, and downwind often enough, to inherit a share of it, on top of whatever the county's own cars and lawn equipment add locally that day.
The valley shape can trap a bad day in place
Frederick sits where Catoctin Mountain, the easternmost ridge of the Blue Ridge, meets the rolling Piedmont, with the city itself in the Monocacy River valley. On the kind of stagnant high-pressure days that also make ozone worst, that same ridge line can slow the west-to-east airflow that would otherwise clear things out, letting warm, hazy air sit over the valley for a day or two before a front finally pushes it through.
Interstate 270, one of the busiest commuter corridors into Washington, runs directly through the city, with I-70 crossing it near downtown. Both add a steady local layer of vehicle exhaust on top of whatever ozone and fine particles have already moved in from the D.C.-Baltimore corridor, which is part of why an afternoon rush-hour reading in Frederick can run a notch worse than a rural monitor a few miles outside the county line.
Smoke does reach Frederick occasionally — just not from a local fire
In early June 2023, smoke from wildfires burning in Quebec and Nova Scotia settled over the entire mid-Atlantic, and Frederick sat inside the same smoke plume as Washington, D.C. and Baltimore. Skies turned orange-gray on June 2, and again more severely from June 6 through June 8, when the wider region recorded some of its worst air quality readings in decades.
That kind of event is rare here — Frederick has no fire season of its own — but it shows the air can still turn bad for a reason that has nothing to do with the county's usual summer ozone pattern. Canairy tracks both: the slow-building smog of a still July afternoon and the rare day when smoke rides in from somewhere else entirely.
Frederick air quality FAQ
What is the air quality in Frederick right now?
As of September 15, 2026 at 8:10 AM EDT, the air quality in Frederick, Maryland is AQI 21 — Good — with PM2.5 at 3.8 µg/m³, the median of 4 live PurpleAir sensors. Open the windows. Great for outdoor activity.
Why does Frederick, MD get smoggy in the summer?
Frederick County is part of the Washington, D.C.-MD-VA area that the EPA classifies as a moderate nonattainment area for ground-level ozone. On hot, sunny, calm days from June through August, vehicle emissions from the D.C.-Baltimore corridor and local traffic on I-270 and I-70 cook into ozone in the afternoon sun, and Frederick's valley setting can slow the wind that would otherwise clear it out.
Does wildfire smoke ever reach Frederick, Maryland?
It's rare, but it happened as recently as June 2023, when smoke from wildfires in Quebec and Nova Scotia settled over the entire mid-Atlantic and turned skies orange-gray from Washington, D.C. to Baltimore, Frederick included. Local fires aren't the region's story here — regional smog is — but Canairy keeps watching for both.
What the AQI numbers mean
| AQI | Category | What it means for you |
|---|---|---|
| 0–50 | Good | Open the windows. Great for outdoor activity. |
| 51–100 | Moderate | Sensitive groups may want to take it slower outside. |
| 101–150 | Unhealthy for Sensitive Groups | Kids, elderly, and respiratory conditions stay closer to home. |
| 151–200 | Unhealthy | Skip outdoor exercise. Close windows. |
| 201–300 | Very Unhealthy | Limit time outside. N95 if you must go. |
| 301+ | Hazardous | Health emergency. Stay inside, run filtration if you have it. |
Canairy lets you tighten these bands if you’re more sensitive than the EPA default, so an alert can fire before the official category changes. How to read the Air Quality Index
Where these readings come from
The AQI at the top of this page is the median of the 4 curated PurpleAir sensors Canairy tracks in and around Frederick, with outliers set aside so that one sensor brought indoors — or parked beside a barbecue — cannot set the number for a whole city. Every sensor behind it is listed above with its distance and bearing from the city center. There is no black box here.
In the app, a place you save resolves the same way first. When no neighborhood sensor is reporting it falls back to the nearest EPA AirNow monitor, and anything modeled rather than measured is labelled a regional estimate rather than passed off as a sensor reading. How low-cost sensors compare to regulatory monitors
About Canairy
Canairy is free to download. The free plan covers one saved place with live readings, a plain-English verdict, and push alerts when the air crosses a threshold you choose. Paid plans add more places, faster refreshes, and SMS alerts. It is built by two parents in Sonoma County, California, who got tired of guessing whether it was safe to send the kids outside. Why we built it
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Air quality near Frederick
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