Air Quality in Cambridge, Massachusetts — Live

Live readings from PurpleAir sensors across Cambridge — with free alerts when wildfire smoke or summer ozone moves in.

Live Cambridge AQI from nearby PurpleAir sensors loads when this page opens in a browser, along with a live sensor map covering Cambridge and Somerville, Arlington, Belmont, Watertown.

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.

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.

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?

This page shows the current AQI for Cambridge, 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.

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 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 Cambridge data come from?

Readings come from PurpleAir's network of laser particle sensors across Cambridge and surrounding towns like Somerville and Arlington, 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.