Well it already happens when big wildfires happen and people have dangerous air around for days. In the short term, keeping everything closed and using masks is

Well it already happens when big wildfires happen and people have dangerous air around for days. In the short term, keeping everything closed and using masks is probably enough. If you mean as a permanent thing, you'd need houses to start having filters on air intake and no openable windows, with instead all air being circulated by the place that has a filter