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

Smoke from wildfires blazing across Canada is once again wafting over huge portions of the U.S. Midwest and worsening air quality there. On August 1 conditions are particularly bad in Minnesota, Iowa and Illinois.

The elevated levels of fine particulate matter resulting from wildfire smoke could present significant health risks.