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Commuters wear masks as wildfire smoke continues to roll across Toronto on Thursday.Sammy Kogan/The Globe and Mail
A day after wildfire smoke turned Canada’s largest city orange, Toronto on Thursday had become grey and hazy as wildfires continued to rage across Northern Ontario.
There are 177 active wildland blazes in Ontario, according to the Ministry of Natural Resources, while more than 870 wildfires are active across Canada. By Thursday evening, orange-level air quality warnings remained in effect for the Greater Toronto Area and parts of Southern Ontario.
Air pollution in Toronto was among the worst in major cities around the world, though Environment Canada said conditions might improve by Friday morning.
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The Globe and Mail spoke to experts about the challenges of forecasting wildfire smoke, how air pollution is measured and why smoke is so bad for our health.
How do we forecast wildfire smoke?
Scientists employ models to predict where wildfire smoke will travel, using the intensity of the fire, wind direction and speed, said Mike Flannigan, a professor of wildland fires at Thompson Rivers University.
Those models have improved over time, he said, but smoke forecasting still presents unique challenges, in part because it’s tricky to know how high up in the atmosphere the smoke will end up. For example, a heat dome can drive warm air toward the Earth’s surface, pushing smoke down with it.
Another challenge lies in predicting the intensity and scope of wildfires, said Dan Jaffe, a professor at the University of Washington who specializes in air quality research.
“If there’s a huge pollution source at this location at this time, I can actually give you a pretty good idea of the direction it’s going and where it’s going to go,” said Prof. Jaffe.
“But the first part of that, which is knowing how much fire and how much smoke it’s going to generate – that’s the hard part. … We can’t tell you if that fire is going to spread or double in size.”
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Wildfire smoke fills the sky above Highway 401 near London, Ont., on Thursday.Carlos Osorio/Reuters
How is air pollution measured?
As of Thursday afternoon, air quality in Toronto remained at high risk, though the pollution level had declined slightly from earlier in the day. According to Environment Canada, smoke conditions could improve by Friday morning.
Toronto’s air quality was ranked worst in the world on Wednesday by IQAir, a Swiss air technology company. By Thursday evening, the city had dropped to fourth place behind Chicago, Detroit and New York, which have also been hit hard by wildfire smoke from Northern Ontario.
Environment Canada’s air quality health index typically measures three pollutants: ground-level ozone, fine particulate matter and nitrogen dioxide.
But wildfire smoke causes rapid spikes in fine particulate matter, known as PM2.5. During smoke events, the agency uses only PM2.5 to update its air quality measures on an hourly basis.
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Why is wildfire smoke so dangerous to human health?
Fine particulate matter refers to a range of solid or liquid particles measuring less than 2.5 microns in diameter – so small they can bypass the body’s defence mechanisms.
“We breathe them deep down into our lungs,” said Ryan Ness, research director on adaptation at the Canadian Climate Institute. “It’s hard for your lungs to rid themselves of that material.”
On smoky days, those particles can aggravate asthma and cause respiratory symptoms in elderly people and young children. Long-term exposure is associated with lung cancers and chronic obstructive pulmonary disease, said Ze’ev Gedalof, director of the Climate and Ecosystem Dynamics Research Lab at the University of Guelph.
“PM2.5 is especially dangerous because if it gets deep into your lungs, it just doesn’t come out,” he said. “There is no safe level of exposure to wildfire smoke.”
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What is the cost of all that smoke?
The Canadian Climate Institute has calculated that the health effects of wildfire smoke cost $231-billion between 2014 and 2025, primarily related to long-term premature mortality.
There’s also an economic impact from people choosing to stay indoors on smoky days, Mr. Ness said. “We know that people go out less, they spend less,” he said. “That is more tricky to measure.”