Air Quality in Gaithersburg, Maryland — Live
Live readings from PurpleAir sensors across Gaithersburg — with free alerts when summer ozone or wildfire smoke moves in.
AQI 49 from 3 PurpleAir sensors · Holding steady · data from PurpleAir
As of , the air quality in Gaithersburg, Maryland is AQI 49 — Good and holding steady — with PM2.5 at 8.8 µg/m³, the median of 3 live PurpleAir sensors reading 32 to 49. 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 Gaithersburg: weeds pollen is the strongest of the three at a 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 Gaithersburg and Rockville, Germantown, Montgomery Village, North Potomac. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Gaithersburg
The sensors Canairy reads in Gaithersburg agree right now — all 3 sit in the Good band, a 17-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| 3.5 mi NW | 49 | Good |
| 3.7 mi WSW | 49 | Good |
| 5.3 mi SE | 32 | Good |
Gaithersburg's air is unremarkable for most of the year — this is a Piedmont suburb of Washington, D.C., with no refineries, ports, or heavy industry, and Montgomery County's gently rolling terrain doesn't trap air the way a mountain valley does. The two things that actually move the needle here are summer heat cooking up ground-level ozone along the region's highway corridors, and the occasional summer stretch when smoke from Canadian wildfires drifts hundreds of miles south and turns a clear sky hazy.
What Canairy does for Gaithersburg
A clear verdict
Not just a number — a plain-English call for Gaithersburg: 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 Gaithersburg or across the country, on one screen.
Ozone, not smoke, is the recurring problem here
Gaithersburg sits entirely within Montgomery County's Piedmont, a stretch of gently rolling terrain that doesn't box in air the way a mountain valley does — there's no ring of hills here holding a temperature inversion in place for days. What Gaithersburg does have is a humid subtropical climate with summer afternoons that average around 85°F, and a spot right on the I-270 corridor, which carries more than 250,000 vehicles a day where it crosses the Rockville interchange just south of the city.
That combination — heat, sun, and a steady stream of tailpipe exhaust — is what cooks up ground-level ozone, the pollutant that drives most of the Washington, D.C. region's bad-air days. I-270 has only gotten busier since a 1990s widening project pulled more homes and businesses up the corridor as far as Germantown, and on hot, still, sunny afternoons the ozone that forms over the highway can push the AQI into Moderate or worse territory well before evening rush hour.
Canadian wildfire smoke has reached Gaithersburg more than once
Gaithersburg has no fires of its own, but it doesn't need one. In June 2023, smoke from wildfires burning in Nova Scotia reached Washington, D.C. and its Maryland suburbs by June 2, and by June 8 it had thickened into some of the worst air quality the region had seen in years — thick enough to postpone a Washington Nationals game that night and put the whole Philadelphia-DC-Trenton corridor under some of the country's worst air. Maryland recorded a measurable spike in cardiopulmonary emergency visits during the two worst stretches that summer, June 6-8 and June 28-30.
That wasn't a one-off. The Metropolitan Washington Council of Governments, which runs the region's air-quality alerts, issued another Code Purple day — its second-highest alert level — on July 17, 2026, again citing smoke drifting down from Canadian wildfires for a spike in fine particle pollution. Gaithersburg is hundreds of miles from the nearest Canadian fire, but smoke this fine doesn't need to be local to be dangerous; it rides in on the jet stream and settles over the whole region at once.
What actually helps on a bad-air day here
Ozone in Gaithersburg follows a predictable clock: it builds through the afternoon as sunlight bakes the day's traffic exhaust, and it is usually worst between roughly 2 and 6 p.m. on hot, sunny days with little wind. Shifting an outdoor run or a kid's practice to the morning, before the ozone has had time to form, is a genuinely useful move on a Code Orange day here — a direct response to how this specific pollutant behaves, not just generic advice.
Wildfire smoke doesn't follow that clock — a plume of Canadian smoke can settle over the area in the morning and sit there all day regardless of temperature. That's the real value of checking a sensor before committing to plans instead of judging by how the sky looks: on a hazy summer day here, the difference between ozone that will clear by evening and smoke that's going to sit on the region all day isn't something you can tell just by squinting at the sun.
Gaithersburg air quality FAQ
What is the air quality in Gaithersburg right now?
As of September 14, 2026 at 8:10 AM EDT, the air quality in Gaithersburg, Maryland is AQI 49 — Good — with PM2.5 at 8.8 µg/m³, the median of 3 live PurpleAir sensors. Open the windows. Great for outdoor activity.
Why does Gaithersburg's air get hazy in summer?
Most of Gaithersburg's bad-air days come from ground-level ozone, not smoke. Hot, humid, sunny afternoons — Montgomery County averages around 85°F on summer days — cook vehicle exhaust from I-270 and the Capital Beltway into ozone, and it tends to peak in the mid-afternoon on still, sunny days rather than overnight.
Does wildfire smoke reach Gaithersburg?
Yes, even though there's no fire anywhere nearby. In June 2023, smoke from wildfires in Nova Scotia gave the Washington, D.C. region, including Gaithersburg, some of its worst air quality in years, and Maryland saw a real spike in emergency visits for heart and lung problems that month. The region's air-quality alert system flagged another Canadian-smoke Code Purple day as recently as July 2026, so it's a recurring risk, not a one-time event.
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 3 curated PurpleAir sensors Canairy tracks in and around Gaithersburg, 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 Gaithersburg
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