Smoke from Canadian wildfires is causing air quality concerns for millions of Americans in the Midwest and Northeast.

Since then, about 2,000 federal firefighters have been sent to Canada in rotations. As of July 17, there were 401 federal firefighters in Canada, many of them in Quebec, the agency said.

These maps show path's timing, how long it lasts. Hundreds of cities in 13 U.S. states fall directly on the April 8 eclipse's path of totality as the moon blocks the sun's disc and ushers in darkness.