Wildfire smoke will linger and spread this weekend. See which cities are most affected.

Huge amounts of wildfire smoke continued to pour into the United States from Canada early Friday as Detroit, Chicago and D.C. topped the list of the world’s most polluted major cities.

The smoke drifted into Baltimore and D.C. overnight, creating very unhealthy air quality with index values of 281 and 247, respectively, as of 6 a.m.