Smoke from Canadian wildfires is causing air quality concerns for millions of Americans in the Midwest and Northeast.
Air quality alerts are in effect Monday in Wisconsin, Michigan, Pennsylvania, New York, Vermont, New Hampshire, Maine, Massachusetts and Delaware.
On Monday morning, Detroit’s air quality was among the worst in the world, ranking third, according to IQAir.
CBS News 
A map of the current Air Quality Index, the federal measurement system, showed ratings of unhealthy and unhealthy for sensitive groups for areas around the Great Lakes and the U.S.-Canada border in the Northeast, Monday morning.
The air index has six ratings:
- Good
- Moderate
- Unhealthy for sensitive groups
- Unhealthy
- Very unhealthy
- Hazardous
Sensitive groups include those who have a heart or lung disease, as well as older adults, children and pregnant women.
The smoke was expected to sink over the next couple of days, impacting more of the Northeast, CBS News meteorologist Rob Marciano said.
There were more than 700 active wildfires in Canada, as of Monday morning, according to the Canadian Interagency Forest Fire Centre.
