How ‘severe and unusual’ smoke from Canadian wildfires is spreading and what it means for your health

Vast portions of eastern Canada and the United States are covered in smoke and haze, as wildfires continue to rage out of control in Quebec.

The smoke has prompted air quality warnings in many cities and towns in Quebec, Ontario and beyond in Canada, and resulted in hazy, apocalyptic skies and warnings in places like New York City and Washington, D.C.

CBC News spoke to experts and consulted recent studies to show the potential health impacts of the smoke in the air — and the extent to which it has spread across eastern North America.

"The levels of air pollution that we're seeing today are severe and unusual in Canada and in parts of the U.S.," said Rebecca Saari, an air quality expert and associate professor in the department of civil and environmental engineering at the University of Waterloo.

"These are poor air quality days, especially in certain areas, where people should be aware and protecting themselves."

She says such events are likely to be more common as climate change intensifies and prolongs the hot, dry conditions wildfires need to thrive.

Overall, Canada is for an especially difficult wildfire season, and federal government officials have said their modelling shows increased wildfire risk in most of Canada through August.

More than 150 forest fires are currently burning in Quebec, with just under 100 of those considered out of control. A storm system off the eastern coast of Nova Scotia has pushed the smoke from those fires toward Ontario and to the U.S., with predictions of poor visibility reaching as far south as North Carolina by day's end.

How bad is the haze?

So, just how bad is this hazy weather?

The air quality in Toronto, for example, ranked among the worst in the world for much of Wednesday, near the level of Delhi, India, and Dhaka, Bangladesh, according to IQair, an online service that monitors and tracks air quality.

The levels in Kingston and points further east in Ontario were considerably worse.

Those areas had among the highest levels of particulate matter — known as PM2.5 levels — in the country.

Those particles are so small — 30 times smaller than the diameter of a human hair — that they can go into the lungs and into the bloodstream, said Dr. Samir Gupta, a respirologist and an associate professor of medicine at the University of Toronto.

"So you can imagine the havoc that they wreak in the lungs themselves," he said.

"That's the most sensitive organ to all of this in terms of breathing symptoms, particularly people who have underlying lung conditions like asthma."

Air quality in terms of cigarettes

A recent Stanford University study quantified what breathing in that particulate matter would mean in terms of cigarettes.

According to the study, an air quality index (AQI) measurement of 20 is equivalent to smoking one cigarette a day. The study noted that exposure to wildfire smoke causing an AQI of 150 for several days would be equivalent to smoking about seven cigarettes a day if someone were outside the whole time.

By that calculation, Kingston residents who spent eight hours outside today smoked the equivalent of nine cigarettes.

Environment Canada's air quality index warned Wednesday of a "very high risk" in eastern Ontario cities, including Kingston, Ottawa and Gatineau, Que.

Other cities in Ontario and Quebec, including Montreal and Toronto, were also ranked as "high risk."

Most of Western Canada had a break from the smoky air after struggling with poor quality last month, except for parts of Vancouver and Central Fraser Valley, which was also under "extreme risk."

If they have been designated as very high risk, Environment Canada advises the general population to reduce or reschedule strenuous outdoor activities. It advised at-risk populations, such as young children, seniors and those with chronic conditions, to avoid strenuous activities altogether.

The air quality has improved in Montreal, where a smog warning was lifted Wednesday afternoon. But it isn't expected to immediately get better further west in parts of Ontario, where it could persist through the weekend.