Tens of millions of people in North America are being urged to wear face masks outdoors after large areas of the US and Canada were blanketed by thick smoke from wildfires.
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 (below left) as it passed through the city earlier this week, before shrouding the Statue of Liberty in New York (below right).
The advice to residents in New York, Philadelphia and Washington DC is to stay inside when possible - but that didn't put these people off taking a fitness class on top of a Manhattan skyscraper.
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.
Firefighters in Canada are still tackling more than 400 blazes across the country, with over 200 of them considered out of control. Thousands of people have been forced to evacuate affected areas.