These two U.S. cities are among the most polluted in the world because of Canadian wildfire smoke  CTV NewsAir quality warnings issued as Manitoba, northwestern Ontario battle wildfire smoke  CityNews WinnipegCanadian wildfires trigger air quality alerts in Midwest U.S.  CTV NewsAir quality warning lifted for Toronto after city saw some of the worst air quality in the world  Toronto StarWildfire Smoke Blankets Chicago With Lollapalooza Music Festival Underway  Bloomberg