system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: In a high-smog area, how is staying inside any safer than going outside?

Isn't it the same air?  Wouldn't I be breathing in about the same amount of smog in my house as the air directly outside my house?
gpt
As mentioned by others there is HVAC filtering, but the big reason is that it keeps people from driving and using other polluting forms of transport. 

Also, if people don't go to work at construction sites there is less dust kicked up and if they don't run factories that produce particulates at full capacity that also cuts down. 

So it's not just staying inside but all the other downstream effects of people not doing things to add more particulates to the atmosphere.