Smoke from Canadian wildfires is causing air quality concerns for millions of Americans in the Midwest and Northeast.
Air quality alerts were in effect Tuesday in several states, including Michigan and New York. New York City and Detroit ranked among the 10 cities around the world with the worst air quality on Tuesday, according to IQAir.
Minnesota, Wisconsin, Illinois, Indiana, Ohio, Vermont, New Hampshire, Massachusetts, Connecticut, Pennsylvania and New Jersey also had active alerts, according to the National Weather Service.
Nikki Nolan 
A map of the current Air Quality Index, the federal measurement system, showed mostly moderate and “unhealthy for sensitive groups” ratings in the states with air quality alerts Tuesday.
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.
There were more than 700 active wildfires in Canada as of Tuesday morning, according to the Canadian Interagency Forest Fire Centre.
