U.S. forest fires make the Big Smoke even smokier, but there's no risk to human health, expert says

Smoke from U.S. forest fires has reached the Big Smoke, but the good news is that the milky haze over the Toronto area poses no danger, according to Environment Canada.

A layer of smoke is in the upper atmosphere and it is not affecting air quality, Peter Kimbell, a warning preparedness meteorologist for Environment Canada based in Ottawa, told CBC Toronto on Tuesday.

"We are seeing forest-fire smoke in Toronto, not only in Toronto, but in most of southern Ontario, southern Quebec, and it's even drifting across the northeastern United States into the Maritimes," Kimbell said in a phone interview.

"It has come a long way and it's not affecting air quality at the surface because most of the heavier particles have kind of fallen out in their voyage from the West Coast to Ontario. But what we do have is a layer of smoke at some altitude aloft and it is making it a bit hazier than it would otherwise be."

The smoke comes from hundreds of wildfires burning in Washington, Oregon and California that have destroyed whole communities and killed at least 36 people. Dozens of blazes have raged with unprecedented scope across some 18,000 square kilometres on the U.S. west coast since August.

The jet stream has brought the smoke to Toronto. It is particularly apparent at morning sunrise and at evening sunset when the sky appears to be an odd colour, often more red or more orange.

Kimbell could not say when the smoke will clear.

"As long the fires continue and the smoke is blowing east from the fires, it could continue for some time," he said.

"It all depends on the jet stream, of course, and the jet stream is in constant state of evolution, so there will be some days that will be hazier than others, but this could last for awhile," Kimbell added.

"There may be one day that will be totally sunny with no smoke, followed by another day that is smokier or hazier than otherwise. It could last for a week or maybe even longer but it's hard to say exactly."

Environment Canada has been fielding calls about the smoke because people want to know why it has travelled this far. Many people have realized that the weather is cloudier than it ought to be, he said.

Tuesday, for example, was forecast to be mainly sunny, Kimbell said.

The smoke poses no danger to human health because it is not low enough in the atmosphere to affect air quality, he added. It's at a high altitude.

"It is interesting to note that some remnants of this forest fire smoke on the West Coast of North America has made its way all the way to Central and even parts of Eastern Canada," he said.

Colette Kennedy, CBC Toronto meteorologist, said a cold front is expected to move into the Greater Toronto Area on Wednesday night and it could push the smoke from the skies.

"Our skies may clear out tomorrow night," Kennedy said on Tuesday.