Smoke from wildfires turns North American skies
There are dozens of wildfires currently burning across Canada, but the prevailing wind has pushed smoke from several large ones in Ontario and Quebec south across the border with the US.
The smog engulfed the CN Tower in Toronto as it passed through the city earlier this week
The advice to residents in New York, Philadelphia and Washington DC is to stay inside when possible
The air quality is so bad in New York that officials are distributing one million masks to residents, with the conditions expected to persist into the weekend.