Canadian wildfire smoke chokes Upper Midwest for second straight year The Associated PressCanadian wildfires trigger air quality alerts across 4 U.S. states Yahoo! VoicesCanada Wildfire Smoke Again Reaching US – Videos from The Weather Channel The Weather ChannelSmoke from Canadian wildfires reaches US, Minnesota under air quality alert ABC NewsSmoke-Filled Skies Leave Midwest Fearing Another Season of Polluted Air The New York Times