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.

Wildfires in Canada are sending heavy smoke across the northern U.S., and New Jersey is experiencing some unhealthy air pollution. The air quality has some Northeasterners wondering, what is the AQI, or Air Quality Index? AQI, or Air Quality Index, is the measure of how healthy or unhealthy the air is.

Millions are under air quality alerts as wildfire smoke blankets large swaths of U.S. Millions of people across the Upper Midwest and the Northeast are under air quality alerts Monday, as smoke from wildfires in Canada drift over the region.