Running any air filter (cheap, expensive, etc) lowers the PM2.5 count in my home (adjacent to a busy 4-lane road in San Francisco) from ~40 to near zero. This is the tool I use to measure PM count: https://www.iqair.com/us/air-quality-monitors/airvisual-pro
https://twitter.com/typesfaster/status/1116732197031956480?c...