Major US east coast cities are experiencing some relief from smoke caused by Canadian wildfires as the haze travels south.
In New York and Washington DC, air quality levels improved from hazardous levels for the first time in two days.
But unhealthy air quality is forecast to hit several southern metropolitan cities, including St. Louis, Missouri and Louisville, Kentucky.
Millions have been under health alerts this week due to the smoke.
The wildfires brought some of the worst levels of air pollution that east coast cities have seen in decades, cancelling outdoor activities and flights in both the US and Canada.
According to the Canadian Interagency Forest Fire Centre, as of Friday, more than 400 wildfires continued to rage in Canada, including more than 200 that are considered out of control.