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.
Photo: National Weather Service New York/Twitter
Looking down the Mississippi River, from Minneapolis towards St. Paul, it's another hazy day in the Twin Cities on June 29 due to the continued affects of the Canadian wildfires. Photo: Deb Pastner/Star Tribune via Getty Images
Wildfire smoke obscures the view of the skyline in Chicago, Illinois, amid an air quality alert as smoke from the hundreds of wildfires in Canada covers the city for a third day in a row on June 29. Photo: Scott Olson/Getty Images
A view from Seville, Spain, of smoke from Canada's fires on June 29. Photo : Francisco J. Olmo/Europa Press via Getty Images
The sun setting in Cascais, Portugal, on June 29 amid a cloud of smoke that's traveled across the Atlantic Ocean from Canada's fires. Photo: Horacio Villalobos#Corbis/Corbis via Getty Images
A ferry passes as the air quality reaches unhealthy levels due to smoke from Canadian wildfires in New York City on June 29. Photo: Selcuk Acar/Anadolu Agency via Getty Images
A group of people wear face masks to protect against air pollution as they walk past the U.S. Supreme Court in Washington, D.C., on June 29. Photo: Anna Moneymaker/Getty Images
People carry on with their daily lives as the air quality reaches unhealthy levels due to smoke from the Canadian wildfires in New York City on June 29. Photo: Fatih Aktas/Anadolu Agency via Getty Images
Photo: NWS Baltimore-Washington/Twitter
A blanket of smoke from wildfires in northern Ontario and Quebec covers the skyline in Kingston, Ontario, Canada, on June 29. Photo: Lars Hagberg/AFP via Getty Images
Photo: Copernicus EU/Twitter
The Toronto, Canada, skyline is seen covered by smoke from the CN Tower as wildfires in northeastern Ontario and Quebec continue to burn on June 28. Photo: Arif Balkan/NurPhoto via Getty Images
More from Axios:
- How Canada's wildfire smoke affects your body
- How to protect yourself from wildfire smoke
- America's most powerful get a close-up of climate change
Editor's note: This article has been updated with more images.
