Clear air in your home might actually be more important than clean air outside.
Fresh air is vital. We can't waste it. But you need clean air in the place where you spend the most time, right? If that place is on top of a mountain, well, good for you. But if that place is in your home, you need your home air to be as fresh as an eagle's cry at the cusp of a golden dawn. SKREEEEEEE! That's your air after you run it through an HEPA purifier like this one.