As Canada continues to battle its worst wildfire season on record, toxic smoke has traveled south and is once again blanketing states across the U.S. A total of 20 states are under air quality alerts Monday, stretching from Montana to New York and as far south as North Carolina and Tennessee as of Monday morning, according to AirNow, an air quality website run by a partnership between the federal government and state and local air quality agencies. Cities including Billings, Montana, Cleveland and Pittsburgh had Air Quality Index ratings of above 150, which is considered “unhealthy.” Meanwhile, residents in Chicago woke up to the fifth worst air quality among major cities worldwide, according to an ABC News analysis.