Will the wildfire smoke from western Canada impact Toronto? Here's what to know

CTV News

04-06-2025

An image of Toronto's skyline taken at around 5 p.m. on June 3. (CP24 Chopper)
The smoke emanating from the forest fires burning across Canada's prairies may be visible in parts of the Greater Toronto Area this week.
There are fires blazing across parts of northwestern Ontario and the Prairies, heading as far west as northern British Columbia, prompting hundreds of people to leave behind their homes and evacuate to another province.
Environment Canada issued several advisories and warnings across four provinces—so will this impact Toronto and the GTA?
What is forecast for Toronto?
Environment Canada meteorologist Barbara Lapido tells CTV News Toronto that many people across southern Ontario might see some hazy skies and red-hued sunrises and sunsets for the next couple of days. FireSmoke Canada, a portal monitoring wildfire and its smoke patterns, also forecasts plumes from the ongoing fires will billow over the GTA through Thursday.
'Some of that smoke (from the forest fires), it's being kind of transported into southern Ontario, but it's not affecting the surface in southern Ontario,' Lapido said, which is why there are no air quality advisories or warnings in place for this region.
Northern Ontario bears the brunt of the wildfire smoke, according to the director of the Southern Ontario Centre for Atmospheric Aerosol Research.
'It's improved since (Monday night) but it's still, I would say, six to eight times higher than it is in Toronto, the level of particles in the air,' Greg Evans said. These microscopic particles—formally called particulate matter—is part of what determines the level of smoke or pollution in the air, subsequently impacting the air quality health index (AQHI).
'When there's a high concentration of them, they scatter the light and so you get this haze that you can see and, once you start seeing that haze, means the concentrations are pretty high,' Evans said.
At around 3 p.m. on Tuesday, the AQHI in Thunder Bay hovered at a seven—a high risk—but hours later it dwindled to a five, a moderate risk (which is exactly what downtown Toronto's index was seeing by 5 p.m.)
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'There's a level at the moment in Thunder Bay of 60 micrograms per (cubic metre) of particular matter, 2.5, which is the pollutant that we worry about for wildfires,' Evans told CTV News Toronto early Tuesday afternoon. 'It was over 400 overnight (…) that's like 40 times the average in Toronto.'
What could the summer look like?
Associate professor at the Dalla Lana School of Public Health, Jeff Brook, thinks what is being seen now with the wildfires is 'an indicator of the potential concern ongoing in the summer.'
'I know that the summer predictions are for there to be considerable heat and dryness in western Canada, and so that means that it's going to be a constant battle to deal with fires and the way the atmosphere moves things,' Brook said. 'We can expect on and off milky skies and periodic bursts of particles on the ground.'
While it's too soon to tell how this will play out this summer, Brook says wildfires are becoming more frequent due to the warming climate—something climatologist Tanzina Mohsin echoes as well.
'We must not consider this as an isolated anomaly with fire events, but we should take this as a stark warning of the new normal that Canadian provinces may face without any urgent actions on climate change, mitigation and adaptation,' Mohsin said.
As fires continue to burn, more carbon gets released into the air, further aggravating the existent problems with climate change—and it is something that will stick around for at least a decade, Evans says.
'The carbon we have in our atmosphere is there for about 40 years, so we're still seeing the impacts now (of) the carbon we released decades ago,' Evans said. 'Even if we do take drastic steps to decarbonize, it's going to take decades for the existing CO₂ in the air to flow to the oceans.'
Decarbonization would require stopping the release of carbon that rises to the atmosphere, which can be done by burning less fossil fuels, Evans adds.
How does wildfire smoke travel?
The energy that emanates from wildfires can push the fine particles high enough into the Earth's atmosphere and into the jet stream, Jeff Brook, an associate professor at the Dalla Lana School of Public Health at the University of Toronto, says.
'The intensity of the fires out in Manitoba, Saskatchewan, have been able to do that,' Brook said, pointing to how Canada's wildfire smoke has crossed the Atlantic toward Europe. The Copernicus Atmosphere Monitoring Service (CAMS) tracked Canadian smoke plumes all the way to Greece and the eastern Mediterranean in mid-May, with more billowing across Europe in the coming days.
As for how smoke travels closer to the ground, Brook could not predict exactly where it will go, as it is weather dependent.
'I would expect Quebec, you know, three years, two years ago, sent quite a bit of it near the ground in Ontario and that's not much further than northwest Ontario,' Brook said. 'So, there's certainly the potential it's going to reach the ground at times in the GTA too.'
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While it's hard to forecast how the prairies' wildfire smoke will continue to impact neighbouring regions over the next few weeks, Evans says it will depend on which way the wind blows, which is largely dependent on the direction of the jet stream—a narrow current of air in the upper levels of the atmosphere.
One benefit for Toronto and southern Ontario, Evan notes, is that spring weather started later this season.
'We've had rainy weather, colder weather in southern Ontario, and that's because we're on the northern side of the jet stream whereas out west, they've had some very hot weather,' Evans explained. 'So, the drawback of having this late spring has actually been beneficial for us in terms of avoiding plumes.'
What AQHI levels should I be concerned about?
When the AQHI reaches a moderate risk level, Lapido says people with pre-existent health conditions, pregnant people, seniors and toddlers may want to start taking some precautions. Some people can be prone to an asthma attack, Evans said, or in more severe cases, a heart attack.
'And when it ticks into the red (a high risk), that's when we have our warning usually or a statement, and that's when (…) the public in general should start paying attention also to these conditions,' the Environment Canada meteorologist said.
Lapido advises avoiding exercise and spending more time indoors with the windows closed when the AQHI gets too high.
There are also long-term impacts of inhaling high amounts of particulate matter from wildfire smoke, should it remain in the air for some time, Evans notes.
'The long-term effects are numerous. It's both cardiac—so the vulnerability to heart attacks, vulnerability to stroke, vulnerability to respiratory problems,' Evans said. 'More recently, there's been connections made to reproductive health, cognitive development, neurological health, cancer—it's right across the board.'
With files from AFP