Millions of people in North America have been advised to wear N95 masks outdoors due to poor air quality levels sparked by intense wildfires in Canada.
New York will begin distributing free masks on Thursday. Canada has said that people should wear a mask if they are unable to remain indoors.
Officials warn that the dangerously smoky conditions are expected to persist into the weekend.
Much of the smoke is coming from Quebec, where 150 fires are burning.
More than 15,000 residents are expected to be forced to evacuate in the province, officials said on Wednesday. It is already Quebec's worst fire season on record.
New York Governor Kathy Hochul announced on Wednesday that New York would distribute one million masks to state residents on Thursday.
"This is a temporary situation. This is not Covid," she said at a news conference. The governor added that New York City buses and trains have high-quality air filtration systems that make them safe forms of travel.
Environment Canada has said that conditions are worsening in Toronto on Thursday, as more smoke pours in.
In a special weather bulletin on Wednesday, the agency recommended that anyone outdoors wear a mask.