Air Quality in Hamilton, Ontario — Live
Live readings from PurpleAir sensors across Hamilton — with free alerts the moment the air turns.
AQI 19 from 5 PurpleAir sensors · Trending down · data from PurpleAir
As of , the air quality in Hamilton, Ontario is AQI 19 — Good and falling — with PM2.5 at 3.5 µg/m³, the median of 5 live PurpleAir sensors reading 12 to 34. 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 Hamilton: 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 Hamilton and Dundas, Ancaster, Stoney Creek, Burlington. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Hamilton
The sensors Canairy reads in Hamilton agree right now — all 5 sit in the Good band, a 22-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| 1.1 mi E | 16 | Good |
| 2.2 mi E | 19 | Good |
| 3.3 mi NNE | 12 | Good |
| 5.1 mi W | 27 | Good |
| 6.4 mi ESE | 34 | Good |
Hamilton is a steel town on the water, and it carries the air quality reputation to match. Ontario's own 2023 air quality report describes a medium-sized city on the western shore of Lake Ontario long associated with air quality challenges, divided by the Niagara Escarpment into the Lower City, which holds the downtown and the industrial zones, and the Upper City above it. The province is blunt about what that geography does: industrial activity and traffic emissions in the Lower City, combined with the geographic constraints, often lead to trapped pollutants. What the measurements add is more complicated than the reputation. In an 18-month study at the ministry's Hamilton Downtown monitor, traffic-related black carbon and steelmaking together made up 5 per cent of the fine-particle mass, while 40 per cent came from secondary organic aerosols carried in from far outside the city.
What Canairy does for Hamilton
A clear verdict
Not just a number — a plain-English call for Hamilton: 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 Hamilton or across the country, on one screen.
The escarpment splits the city's air in two
Ontario runs three air monitoring stations in Hamilton, and their names describe the split exactly: Hamilton Downtown, Hamilton West and Hamilton Mountain. Two of them sit below the escarpment with the harbour and the mills, one sits on top. That is unusual. Most Canadian cities this size get one station and a citywide number derived from it, so the province is effectively conceding here that a single figure would not describe Hamilton honestly.
The seasons move the sources around too. The ministry's study of PM2.5 in the Lower City, which ran from 12 January 2021 to 16 July 2022, found sulphates peaking in summer, nitrates and traffic-related pollution highest in winter, and local pollution at its maximum in spring. Summer levels were driven up mainly by wildfires and regional sources, while winter air was dominated by local emissions, particularly traffic, with local industrial and traffic pollution peaking during weekday morning rush hours. In practice that means the reason your air is bad in July is usually not the same as the reason it is bad in January.
The mills are still what people notice
ArcelorMittal Dofasco, Canada's largest steel producer, sits on Hamilton Harbour, and its coke ovens release soot along with benzene and benzo(a)pyrene. For years Ontario's environment ministry permitted the company to emit benzene, benzo(a)pyrene, manganese and suspended particulate well above provincial standards under site-specific standards. At one point Dofasco could release 22 times more benzene than the general limit. Those exemptions expired in 2023, and by the company's own 2023 annual report it was still emitting above the standards; similar exemptions for Stelco and Harsco Canada expired around the same time, with the ministry saying it is finalising a single technical standard for all steel plants instead.
The version residents actually see is more sudden. On 9 February 2015 a blast furnace safety valve released, and a black cloud drifted over Grenfell Street, near Beach Road and Kenilworth Avenue North, coating snowbanks, houses and cars in coarse black grit. The area councillor fielded complaints about the fallout from as far away as the east Mountain. Dofasco was convicted and ordered to pay $162,500 in January 2018. Some of this is changing: Dofasco shut its No. 3 coke plant on 13 April 2026, roughly 30 per cent of its coke output, having closed No. 1 back in 2015, and in 2022 announced a $1.8-billion project to move from coal to natural gas by 2028 and cut emissions by 60 per cent. One coke plant still runs at Dofasco and another at Stelco.
Who actually measures the air here
Hamilton has a second monitoring network most cities do not. Since 1 May 2003 the point-source air monitoring network in the City of Hamilton has been operated and maintained by the Hamilton Air Monitoring Network, an industry-funded body of 22 local companies set up under the ministry's Source Emissions Monitoring program. It measures sulphur dioxide, total reduced sulphur, oxides of nitrogen, PM2.5 and PM10, total suspended particulates, volatile organic compounds and polycyclic aromatic hydrocarbons, posts the readings in near real time, and its reports are audited by the ministry.
That is more industrial monitoring than almost anywhere else in Canada, and it is pointed squarely at the bay. What it is not designed to tell you is what the air is doing on your own street in Westdale, in Crown Point, or up on the Mountain on a still morning. That is the gap the PurpleAir sensors on the map below fill.
Hamilton air quality FAQ
What is the air quality in Hamilton right now?
As of September 11, 2026 at 8:10 AM EDT, the air quality in Hamilton, Ontario is AQI 19 — Good — with PM2.5 at 3.5 µg/m³, the median of 5 live PurpleAir sensors. Open the windows. Great for outdoor activity.
Why is there smoke in Hamilton today?
In summer the usual answer is wildfire smoke that started nowhere near Hamilton. Ontario's own analysis of fine particulate in the Lower City found summer levels were significantly affected by wildfires and regional sources, and that about 40 per cent of the PM2.5 mass came from long-range atmospheric transport. Closer to home, the industrial waterfront occasionally produces a visible fallout event rather than a haze, as it did on 9 February 2015 when a blast furnace release dropped black grit over Grenfell Street and drew complaints as far as the east Mountain. If the sky looks hazy citywide it is usually smoke from elsewhere; if grit is landing on your car, it is not.
Canada reports the AQHI, so why does this page show a different number?
Environment and Climate Change Canada publishes the Air Quality Health Index, a 1 to 10+ scale built from three pollutants measured together: fine particulate matter, ground-level ozone and nitrogen dioxide. PurpleAir sensors measure fine particulate matter only, so an AQHI cannot honestly be calculated from them. This page shows the US EPA AQI instead, which is derived from PM2.5 directly and is what most air quality apps use. It is not an AQHI and Canairy does not present it as one. For the official AQHI for Hamilton, Environment Canada and Ontario's air monitoring stations are the sources.
Do the steel mills still affect Hamilton's air?
Yes, but not in the way the skyline suggests. By mass, the ministry's Lower City study attributed 5 per cent of fine particulate to traffic-related black carbon and steelmaking combined, with far more coming from traffic and from pollution blown in regionally. The mills matter more for the specific contaminants they emit: benzene, benzo(a)pyrene and manganese, which the province allowed above standard for years under site-specific exemptions that have since expired. A PurpleAir sensor measures particle mass, not what the particles are made of, so it will show you a dusty day but cannot identify benzene.
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 Hamilton, 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 Hamilton
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