I use PurpleAir data for a lot of my home automations— I have a smart window vent and configure it to blow in/out depending on which side has the worse air.

(Thank you to those who maintain public sensors!)

I do notice that in my neighborhood (Noe Valley) a lot of the sensors are very incorrect or often offline. I've resorted to taking the median and throwing outliers away, but even this often doesn't work. This is the challenge of relying on crowdsourced data I suppose...