Air Quality in Nashua, New Hampshire — Live
Live readings from PurpleAir sensors across Nashua — with free alerts when summer ozone climbs or wildfire smoke rolls in.
AQI 25 from 3 PurpleAir sensors · Trending up · data from PurpleAir
As of , the air quality in Nashua, New Hampshire is AQI 25 — Good and rising — with PM2.5 at 4.5 µg/m³, the median of 3 live PurpleAir sensors reading 17 to 28. 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 Nashua: 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 Nashua and Hudson, Merrimack, Hollis, Amherst. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Nashua
The sensors Canairy reads in Nashua agree right now — all 3 sit in the Good band, a 11-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| City center | 28 | Good |
| 2.6 mi WSW | 25 | Good |
| 5.9 mi SW | 17 | Good |
Most of the year, Nashua's air is genuinely good — flat Merrimack Valley terrain and New England's brisk prevailing winds keep pollution moving through rather than settling in. The exception is summer: on hot, hazy, calm days between April and September, ground-level ozone can build up over southern New Hampshire, some of it made locally by Everett Turnpike traffic baking in the sun, much of it riding in on the same stagnant air mass that has already cooked for a day or two over New York City and Boston. Every few years, smoke drifting down from Quebec adds a second, very different kind of bad-air day that has nothing to do with local weather at all.
What Canairy does for Nashua
A clear verdict
Not just a number — a plain-English call for Nashua: 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 Nashua or across the country, on one screen.
What the air in Nashua is doing next
| When | Expected air quality | Main pollutant |
|---|---|---|
| Today | Good | ozone |
Forecast from EPA AirNow for the Hillsborough County 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.
Nashua's ozone problem starts hundreds of miles away
New Hampshire is one of thirteen jurisdictions in the Ozone Transport Commission, a multi-state body created under the Clean Air Act in 1991 specifically because ground-level ozone does not respect state lines. Nitrogen oxides and volatile organic compounds from the Washington-to-Boston corridor drift northeast and cook into ozone in the same sunlight that falls on Hillsborough County, so a still, hot day in Nashua can carry a load of smog that started as tailpipe and smokestack exhaust two states away.
The state's own forecasters track this closely: New Hampshire DES issues ozone forecasts every day from April through September, broken out by ten county-level zones, and Hillsborough County — Nashua's zone — gets its own daily call. An Air Quality Action Day is called when that transported ozone combines with local traffic on the Everett Turnpike and Route 3 and the day's heat and sun are enough to push levels into unhealthy territory, typically on the stagnant, high-pressure afternoons of July and August.
The summer of 2023 showed how far wildfire smoke can travel
On June 6, 2023, the EPA issued an air quality alert naming the central, southern, and western parts of New Hampshire — Nashua's part of the state — as likely to exceed the federal 24-hour standard for fine particle pollution, as smoke from record Quebec wildfires poured south into the Northeast on a counterclockwise flow around a low-pressure system. Health officials told sensitive groups to stay indoors with windows closed and avoid strenuous outdoor activity while the haze hung over the region.
New Hampshire's own environmental agency later noted that the state was largely spared the worst of that smoke — the choking, orange-sky days that hit New York and Pennsylvania harder — but it still logged seven separate Air Quality Action Days that summer, well above a typical year. That is the lesson Nashua residents took from 2023: you do not need to be under the thickest part of a Canadian wildfire plume to end up with air that is genuinely unhealthy to breathe.
Winter adds a slower-building particle problem
Ozone and imported smoke are warm-weather stories; winter in Nashua brings a quieter one. Many New Hampshire homes supplement or replace furnace heat with wood stoves and fireplaces, and on cold, calm nights that smoke has nowhere to go. Research on residential wood burning nationally puts it at roughly a fifth of all winter fine-particle pollution, and New Hampshire's own environmental agency has run public advisories urging residents to burn only seasoned wood and keep fires hot enough to burn cleanly, precisely because wood smoke is a measurably bigger piece of the winter air-quality picture than most people assume.
New Hampshire DES has backed that message with action elsewhere in the state — the City of Keene's woodstove changeout program, running since 2009, offered rebates to replace older, dirtier stoves — evidence that state regulators treat wood smoke as a real and addressable source, not just a cozy inconvenience. For a Nashua household that heats with wood, checking the day's PM2.5 reading before a bitter, windless night is as useful a habit as checking it before a smoky August afternoon.
Nashua air quality FAQ
What is the air quality in Nashua right now?
As of September 15, 2026 at 8:10 AM EDT, the air quality in Nashua, New Hampshire is AQI 25 — Good — with PM2.5 at 4.5 µg/m³, the median of 3 live PurpleAir sensors. Open the windows. Great for outdoor activity.
Why does Nashua's air get worse in summer?
Southern New Hampshire sits downwind of the Boston-to-New York corridor, and on hot, calm days from April through September, ozone that forms over that corridor drifts northeast and combines with local traffic on the Everett Turnpike and Route 3. New Hampshire's environmental agency forecasts ozone by county and calls an Air Quality Action Day when the combination of transported and local pollution is expected to reach unhealthy levels.
Did the 2023 Canadian wildfires affect Nashua?
Yes, though less severely than states farther south. On June 6, 2023, the EPA issued an air quality alert for central, southern, and western New Hampshire — which includes Hillsborough County — as smoke from record Quebec wildfires pushed fine particle pollution to unhealthy-for-sensitive-groups levels. New Hampshire logged seven Air Quality Action Days that summer, more than a typical year, even though the state avoided the worst of the smoke that hit New York.
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 Nashua, 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 Nashua
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