Smoke from Canadian wildfires in British Columbia, Alberta and western Ontario is moving south and the state Pollution Control Agency has expanded an air quality alert to the southern half of Minnesota beginning at 8 p-m tonight through noon Sunday. An alert has already been in effect in the northern half of the state since yesterday afternoon. Air pollution can aggravate heart and cardiovascular disease as well as lung diseases like asthma and COPD. Officials say by Sunday afternoon winds will switch to the south and air quality will improve.