Hundreds of wildfires still burning in Canada are expected to undermine air quality across the Upper Midwest and Northeast into Tuesday.

When combined with the Philly area’s warm, sunny weather, the incoming smoke stands to increase levels of ozone, the Pennsylvania Department of Environmental Protection said.

Wildfires burning in Canada were causing unhealthy air quality across parts of North America on Monday. Canadian wildfires burning across northern Manitoba and Saskatchewan are sending smoke through central Canada,