Air Quality in Frederick, Maryland — Live

Live readings from PurpleAir sensors across Frederick — with free alerts when summer ozone turns the air unhealthy.

Live Frederick AQI from nearby PurpleAir sensors loads when this page opens in a browser, along with a live sensor map covering Frederick and Middletown, Urbana, Thurmont, Emmitsburg.

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.

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.

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?

This page shows the current AQI for Frederick, calculated from PurpleAir sensors across the city and updated continuously. The map below shows every live sensor, so you can check the reading closest to your own neighborhood.

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 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.

Where does Canairy's Frederick data come from?

Readings come from PurpleAir's network of laser particle sensors across Frederick and surrounding towns, cross-referenced with government monitors and the Google Air Quality API. You can see every sensor behind your numbers on the live map - there's no black box.

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.