I live in the area labeled "the triangle of death" where the winter air quality is indeed insidiously deadly for some of us. My activity is dependent upon the levels of local PM2.5, which i can now assess quantitatively by the monitor on my property. It validates the symptoms of burning eyes and throat and a tightness in my chest but doesn't do much to clean up the air.  My air exchanger (HRV) system has extra filtration downstream to filter out the pollution so the inside air is quite clean. A few weeks ago, the unit was down for repair and i awoke to the smell of coal smoke! Outside air measured 358 ug/m3. It was -30 F. I couldn't get away from the air. Best Christmas present this year was to have my air exchanger up and filtering again! I don't shovel snow and minimize outside chores when the air is nasty, and am essentially forced to remain inside. It is foolish to ignore the medical and scientific evidence of this issue.