Air Quality in Cambridge, Massachusetts — Live
Live readings from PurpleAir sensors across Cambridge — with free alerts when wildfire smoke or summer ozone moves in.
AQI 5 from 5 PurpleAir sensors · Trending down · data from PurpleAir
As of , the air quality in Cambridge, Massachusetts is AQI 5 — Good and falling — with PM2.5 at 1.0 µg/m³, the median of 5 live PurpleAir sensors reading 1 to 14. 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 Cambridge: weeds pollen is the strongest of the three at a low 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 Cambridge and Somerville, Arlington, Belmont, Watertown. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Cambridge
The sensors Canairy reads in Cambridge agree right now — all 5 sit in the Good band, a 13-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| 1.4 mi WNW | 6 | Good |
| 1.5 mi SW | 7 | Good |
| 2.2 mi N | 1 | Good |
| 2.9 mi SW | 5 | Good |
| 3.1 mi ESE | 14 | Good |
Cambridge's air is good most of the year. Middlesex County's EPA monitors logged a median 'Good' reading on more than three of every four days in 2025, and the county recorded zero fully unhealthy days. What does periodically push it worse is ground-level ozone on hot, still summer afternoons — the state forecasts ozone from April through October — and, less often but more sharply, wildfire smoke drifting down from Canada, which has reached Cambridge twice in the last few years, most recently in mid-July 2026.
What Canairy does for Cambridge
A clear verdict
Not just a number — a plain-English call for Cambridge: 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 Cambridge or across the country, on one screen.
Canadian wildfire smoke has reached Cambridge twice in three years
In early June 2023, smoke from wildfires burning in Quebec and Northern Ontario spread across the Northeast, and by July 1 that year the EPA was warning that fine-particle pollution from the same fires threatened to push Massachusetts (outside Cape Cod and the Islands) over federal 24-hour health standards, with hazy skies, reduced visibility, and the smell of burning wood reported region-wide. Boston itself was spared the very worst of that June smoke — an upper-level low-pressure system parked over Maine steered the thickest plume toward New York City instead, and Boston's air actually read 'Good' the day NYC's was briefly the worst of any major city on Earth.
Cambridge's luck did not hold the second time. On July 15, 2026, smoke from wildfires burning in Ontario and northern Minnesota rode the jet stream directly into New England, turning the sky a milky yellow-brown and pushing Boston-area AQI to roughly 130 — Unhealthy for Sensitive Groups — with a second wave forecast for the following afternoon. Massachusetts environmental officials told residents with asthma or COPD to watch conditions closely and limit outdoor time, a reminder that this is now a recurring risk here, not a one-off.
Ground-level ozone, not smoke, is the everyday problem
Massachusetts forecasts for ozone, not fire smoke, every day from April through October, and the numbers show why: across Middlesex County's EPA monitors in 2025, ozone was the pollutant behind 152 of 243 measured days — nearly two-thirds of the year's readings — versus 90 days led by fine particles. The county's worst single day still only reached AQI 105, barely into Unhealthy for Sensitive Groups, which is the normal shape of an ozone problem here: rarely severe, but a steady background presence most of the warm season.
Ozone is not a plume you can see arrive the way smoke is. It forms through the afternoon as sunlight cooks vehicle and industrial exhaust, building through hot, humid, light-wind stretches and typically peaking in the mid-afternoon to early evening rather than at commute hours. Cambridge has no ridge or valley to trap it the way inland New England towns do, but it sits inside the same humid Northeast air mass that bakes up ozone from New York to Boston, so a hazy, still July afternoon can mean the day's worst reading is still ahead of you at 4 or 5 p.m.
Traffic corridors add a layer a citywide number misses
Cambridge is flat and dense — just 6.4 square miles of land — so unlike a valley town, its pollution story is shaped by where the traffic runs rather than where the terrain traps it. Route 2 and the Alewife Brook Parkway interchange in North Cambridge carry heavy daily commuter volume, enough that a dedicated nonprofit, the Alewife Transportation Management Association, works specifically to cut congestion and vehicle-related air pollution in that corridor. Memorial Drive along the Charles River and the approaches near the river dam concentrate exhaust in a similar way closer to the water.
That means a countywide 'Good' reading can sit right alongside a noticeably worse block near a highway ramp — mapping and pollution studies of the Boston area consistently find concentrations highest in the dense urban centers of Boston, Cambridge, Chelsea, and Everett, tracking population density and traffic rather than any single citywide source. It's exactly the gap a neighborhood-level sensor reading is built to catch, rather than one regional monitor miles from where you actually live.
Cambridge air quality FAQ
What is the air quality in Cambridge right now?
As of September 14, 2026 at 12:37 PM EDT, the air quality in Cambridge, Massachusetts is AQI 5 — Good — with PM2.5 at 1.0 µg/m³, the median of 5 live PurpleAir sensors. Open the windows. Great for outdoor activity.
Does wildfire smoke reach Cambridge?
Yes, though it's the exception rather than the rule. Smoke from Quebec and Ontario wildfires spread across the Northeast in June 2023, and Massachusetts was still under EPA fine-particle warnings into July 1 that year. More recently, smoke from wildfires in Ontario and northern Minnesota pushed Boston-area AQI to roughly 130 on July 15, 2026. Both events passed within days, but they show up on the sensor map in real time.
Why does Cambridge's air get hazy in summer?
Ground-level ozone, not smoke, is the usual cause. Massachusetts forecasts ozone every day from April through October, and it was the lead pollutant on about two-thirds of Middlesex County's measured days in 2025. It forms when sunlight bakes vehicle exhaust through the afternoon, so a hot, humid, light-wind day tends to get hazier as it goes rather than clearing by evening.
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 5 curated PurpleAir sensors Canairy tracks in and around Cambridge, 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 Cambridge
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