Air Quality in Hamilton, Ontario — Live
Live readings from PurpleAir sensors across Hamilton — with free alerts the moment the air turns.
Live Hamilton AQI from nearby PurpleAir sensors loads when this page opens in a browser, along with a live sensor map covering Hamilton and Dundas, Ancaster, Stoney Creek, Burlington.
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.
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.
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
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.
What is the air quality in Hamilton right now?
This page shows the current AQI for Hamilton, calculated from PurpleAir sensors across the city and updated continuously. It is worth checking the map rather than the headline number, because Hamilton's air genuinely differs by elevation. Ontario runs its three stations as Hamilton Downtown, Hamilton West and Hamilton Mountain for exactly that reason, and the sensor nearest your street is a better guide than any citywide average.
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 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.
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.