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Ontario's air can change in an afternoon. A clear morning in Mississauga can give way to a smoky Tuesday by dinner — drifting in from a fire two provinces away that you didn't even know was burning. Pollen ramps up in May. Ozone climbs on hot July afternoons in the Golden Horseshoe. And the long furnace season, from October through April, keeps your indoor air working hard for half the year. This page gives you the live AQI map and the practical steps that actually help.
If you're in a hurry, here's the short version.
Today's Ontario AQI: Check the live map at the top of this page — readings update throughout the day for every major city.
AQI vs. AQHI: AQI (0–500) is international; AQHI (1–10+) is Canada's official scale. Both point at the same underlying air.
Safe threshold: AQI 0–50 is good. Above 100, sensitive groups should limit outdoor time. Above 150, everyone should.
Main cause in summer: Wildfire smoke, often drifting in from outside Ontario. PM2.5 is the pollutant that matters most.
Best filter for smoke: MERV 13 (Optimal). For odors that linger after smoke, the Odor Eliminator filter.
What to do today: Check the map. Close windows if AQI is above 100. Run the HVAC fan. Change the filter if it's been a while.
Ontario's air quality varies dramatically by region, season, and even hour — always check the live reading before making outdoor plans.
Canada's official scale is the AQHI (1–10+), but most maps and searches use the international AQI (0–500). This page shows AQI; the resources above link to the AQHI.
The biggest threats to Ontario air quality are wildfire smoke (June–September), spring pollen, summer ozone, and winter inversions in urban corridors.
PM2.5 — fine particulate matter from wildfire smoke — is the pollutant most reliably stopped by a MERV 13 (Optimal) filter.
Sensitive groups (children, older adults, asthma and COPD patients) need to act on the AQI sooner than the general population — even a moderate reading can trigger symptoms.
During heavy smoke events, close windows, run your HVAC fan continuously, and change your filter more often than usual.
A clean Filterbuy filter — Standard (MERV 8), Superior (MERV 11), Optimal (MERV 13), or odor Eliminator — is the simplest practical lever you can pull at home.
Free shipping to Canada on every order, no minimum, with prices shown in CAD.
The map at the top of this page shows real-time air quality readings for every region of Ontario, from Windsor and London through the Greater Toronto Area and Ottawa, up to Sudbury and Thunder Bay. Readings update throughout the day. The number itself — that AQI value sitting on your screen — is a snapshot of how clean (or not) the outdoor air is right now in your area.
On the international Air Quality Index (AQI) scale used on this map, anything from 0 to 50 is considered good for the general population. From 51 to 100, the air is generally acceptable, though unusually sensitive people may notice symptoms. Above 100, sensitive groups — children, older adults, anyone with asthma or COPD — should start limiting prolonged time outdoors. Above 150, it's a sensible day for everyone to stay in.
Canada also uses its own official scale, the Air Quality Health Index (AQHI), which runs from 1 to 10+. The AQHI is published by Environment and Climate Change Canada and is built around the specific health risks of three pollutants: fine particulate matter (PM2.5), ground-level ozone (O₃), and nitrogen dioxide (NO₂). You'll see both scales referenced across Ontario — this page leans on AQI because that's the scale most people search for, but we point you to the AQHI in the resources below for the official Canadian reading.
What pushes Ontario's number up varies by season. Wildfire smoke from Northern Ontario, Québec, and the Prairies dominates summer readings — increasingly so over the last few years. Spring brings pollen and mould spores. Hot, sunny summer afternoons cook up ground-level ozone in southern Ontario. Winter inversions trap vehicle and industrial emissions closer to the ground across the GTA and the Hamilton industrial corridor. Knowing which one is driving today's reading is half the battle, and it's what tells you whether to close the windows, upgrade the filter, or just carry on.
After fifteen years on Ontario service calls, the pattern I see is consistent — the homeowners who weather smoke events well aren't the ones with fancy equipment. They're the ones who checked the map before opening the windows. A clean Optimal (MERV 13) filter in a furnace that's actually running on the fan setting will pull more fine smoke out of the air over a day than most people expect. The trick is doing it early, before the smoke settles into your fabrics and carpets. By the time you can smell it indoors, you're playing catch-up.
— Filterbuy Canada
These are the sources we trust for current readings, health guidance, and longer-term context. Save them somewhere you can find quickly during smoke season — you'll be glad you did.
The official Government of Canada source. The provincial summary view shows current AQHI values and forecast maximums for cities across Ontario, updated continuously. This is the page to trust when you want the federally validated number, not a third-party reading.
→ weather.gc.ca — Ontario AQHI provincial summary
Ontario's own provincial air quality monitoring network. The MECP runs the stations that feed into the national AQHI for Ontario, and their site offers a station-by-station view, historical data, and pollutant-specific deep dives that go beyond what the national page shows.
→ airqualityontario.com — Ontario MECP air quality portal
When the outdoor AQI climbs, this is the page that tells you what to actually do inside your home. Health Canada's official residential guidance on PM2.5 covers furnace and HVAC strategies, ventilation rules of thumb, and what to prioritise if you have someone with a respiratory condition in the household.
→ canada.ca — Health Canada PM2.5 indoor air guidance
A practical, plain-language guide written by Canadians for Canadian conditions. Covers who is most at risk, why ordinary masks don't help, and concrete steps for keeping smoke out of your home during an active fire-smoke event in Ontario.
→ lung.ca — Wildfire smoke and lung health
The WHO sets the benchmark numbers that most national agencies, including Health Canada, reference when establishing exposure thresholds. The European fact sheet is the most accessible WHO entry point and explains the 2021 guideline update that significantly lowered the recommended PM2.5 limit.
→ who.int — Air quality fact sheet
If you're not sure what the AQI numbers actually represent — how the scale is calculated, why the United States, Canada, and the EU each use slightly different versions, and how AQI compares to AQHI — this overview is the cleanest starting point with citations to the underlying agency documentation.
→ en.wikipedia.org — Air Quality Index
Our companion live map for active forest fires and smoke plumes across Canada. Pair it with the AQI map on this page: the AQI tells you what the air is doing right now, and the smoke map tells you where the smoke is coming from and where it's headed next.
→ filterbuy.com — Live Canadian wildfire and smoke map
The data below comes from three different sources — peer-reviewed research, federal statistical analysis, and frontline health advocacy — so you're not relying on one perspective.
The 2023 fire season was the worst in Canada's recorded history. Researchers writing in Nature Communications documented that approximately 15 million hectares burned, more than doubling the previous record of 6.7 million hectares set in 1989.
The smoke from these fires reached major population centres more than 1,000 kilometres away, including southern Ontario, which is why a fire in northern Saskatchewan can show up as a poor AQI reading in Toronto.
Source: Nature Communications — Drivers and Impacts of the 2023 Canadian Wildfire Season
Statistics Canada's national exposure analysis found that residential PM2.5 exposure averaged 8.03 µg/m³ in urban cores, compared with 4.32 µg/m³ in rural areas — roughly a 1.9× difference.
PM2.5 exposure was especially high in parts of southern Ontario, particularly around Toronto and Windsor. If you live in the GTA, the Golden Horseshoe, or the Windsor-Detroit corridor, your baseline air is consistently working against you more than the national average.
Source: Statistics Canada — Exposure to Fine Particulate Matter Air Pollution in Canada
The Canadian Lung Association notes that for anyone diagnosed with a chronic lung condition such as asthma or COPD, even an AQHI score of 4 — which falls in the moderate range and is considered safe for the general population — can be enough to worsen symptoms.
That's a meaningful threshold to know if you or a family member has a respiratory diagnosis. It's also why the “general public” advice line and the “at-risk population” advice line on the AQHI scale exist as two separate sets of guidance.
Source: Canadian Lung Association — How to protect your lungs from wildfire smoke
Here's the honest read. The trend lines for Ontario aren't catastrophic, but they aren't reassuring either. Wildfire smoke events are becoming a regular feature of summer in southern Ontario, not an occasional anomaly. Spring allergy seasons are arriving earlier and lasting longer. The furnace season — already six to eight months in most of the province — isn't getting any shorter. None of that requires panic, but all of it requires a slightly more attentive approach to indoor air than households needed a decade ago.
Our view, after years of helping Canadian homeowners through smoke events: most people overinvest in expensive standalone air purifiers and underinvest in the filter that's already running through their HVAC system for half the year. A well-chosen pleated filter in the furnace, changed on a sensible schedule, does an enormous amount of quiet work. During wildfire smoke season, an Optimal (MERV 13) filter captures the fine PM2.5 particles that lower MERV ratings let pass. During spring allergy season, a Superior (MERV 11) filter handles pollen, dust mites, and mould spores comfortably. During lingering smoke odors, an odor Eliminator filter does what its name suggests.
We won't oversell it. A furnace filter is not a respirator, and it doesn't make outdoor smoke disappear. But for the air inside your home — where most Ontarians spend roughly 90% of their waking hours, especially through the long heating months — it is one of the highest-leverage things you can change. Cleaner filter, fan running, windows closed during high-AQI events. That's the playbook.
Practical steps you can take in the next few minutes, depending on what today's reading is telling you.
Open the windows. Air out the house if you've had them closed.
Check when you last changed your furnace filter. If it's been more than 60 days, set a reminder.
If you don't have a subscription set up yet, this is a calm day to do it.
Carry on normally, but check on anyone in your household with asthma, COPD, or pollen allergies — moderate days are often when symptoms start showing up before the number climbs.
If you're due for a filter change, do it today rather than waiting.
Close the windows. Switch your HVAC system to the fan setting so air keeps circulating through your filter.
Limit outdoor time for children, older adults, and anyone with a respiratory condition.
Check the filter. If it's visibly discoloured, replace it now.
Stay indoors. Keep windows and doors closed. Run the HVAC fan continuously.
If you have one, an Optimal (MERV 13) filter or an Odor Eliminator filter is your best in-home defence.
Check on neighbours — particularly older neighbours and those living alone.
If you or anyone in your home experiences chest tightness, persistent coughing, or shortness of breath, contact a healthcare provider or call Telehealth Ontario at 811.
Ontario's air quality varies by region and changes hour by hour. The live map at the top of this page shows current AQI readings for major cities — including Toronto, Ottawa, Mississauga, Hamilton, London, Kitchener-Waterloo, Windsor, and Sudbury — alongside the timestamp of the latest update. For a single province-wide picture, check the average reading shown beneath the map.
“Bad” depends on your situation. An AQI under 50 is considered good for everyone. From 51 to 100, air quality is generally acceptable, though unusually sensitive people may notice symptoms. Above 100, sensitive groups — children, older adults, and people with asthma — should limit prolonged outdoor activity. Check the live reading for your specific area at the top of this page.
Health Canada and Environment and Climate Change Canada use the AQHI (1–10+) as the official scale, where 1–3 is low risk and 7 or higher is high risk. On the AQI scale used on most maps, readings of 0–50 are considered safe for the general population. For sensitive individuals, anything above 100 warrants caution.
The AQHI is Canada's official health-based scale, running from 1 (low risk) to 10+ (very high risk). The AQI is an internationally used scale running from 0 to 500. They measure related things but use different formulas. This page displays AQI because it is the most widely searched scale; for the official Canadian reading, Environment and Climate Change Canada publishes AQHI on weather.gc.ca.
The most common causes are wildfire smoke (especially June through September), ground-level ozone on hot summer afternoons, spring pollen and mould spores, vehicle emissions in the GTA and Golden Horseshoe, and winter inversions during the long heating season. Today's specific driver is usually noted in Environment and Climate Change Canada's daily air quality forecast.
When AQI is above 100, keep windows and doors closed, limit outdoor activity for children and older adults, and run your HVAC system on the fan setting so air keeps circulating through your filter. Upgrade to a MERV 13 (Optimal) filter during wildfire smoke season — it captures the fine particles that lower MERV ratings miss — and replace it more often during heavy smoke events.
MERV 13 (our Optimal rating) is the best choice for wildfire smoke. It captures fine particles, including PM2.5, which is the main concern in smoke. MERV 11 (Superior) still captures dust, pollen, and pet dander but lets more of the smallest smoke particles through. For lingering smoke odors, an odor Eliminator filter pairs well with regular pleated filtration.
Filterbuy generally recommends every 60 to 90 days, but during active wildfire smoke events, you should check more often — every 30 days is reasonable, and visible discolouration on the filter is a clear signal it is time to swap. Canadian homes run their furnaces six to eight months a year, so a subscription scheduled around the heating season keeps you ahead of replacements.
If today's reading has you thinking about your home's air, you're already a step ahead. Filterbuy ships pleated air filters in more than 600 sizes — including custom — direct from our facilities to your door in Ontario. Free shipping across Canada on every order, no minimum, prices shown in CAD at checkout.
Not sure which filter you need? Our Superior (MERV 11) handles spring allergies and pet dander. Our Optimal (MERV 13) is the one we recommend for wildfire smoke season. Our odor Eliminator clears the lingering smell that often outlasts the worst readings. A short guide on our shop page walks you through which fits your home in about a minute.
Subscribe and save up to 70% per filter with auto-delivery — edit, skip, or cancel anytime. Or order a single pack today and try us out. We've earned over 85,000 five-star reviews from customers across North America, and we'd rather earn your trust than push you into the wrong product.
Air quality readings on this page are provided for informational purposes. If you or a family member is experiencing respiratory symptoms, please contact a healthcare provider or call Telehealth Ontario at 811.
Questions? Call us toll-free at (855) 345-8289 or email info@filterbuy.com.
Filterbuy Canada, 96 Carrier Dr, Toronto, ON M9W 5R1.
