Air quality alerts were issued in cities across some 23 U.S. states Thursday as lingering smoke from Canada's worst-ever wildfire season continued to pose a health threat to millions of Americans.
The big picture: Detroit, D.C., New York City and Toronto endured some of the world's worst air quality Thursday, per Swiss air technology company IQAir. Alerts stretched from Colorado to Vermont and down to Georgia. Canadian officials warn this extreme weather event will likely last all summer as climate change leads to more instances of critical fire weather.
