Not so sure these reflect actual air qual. There are places that read 0 or very low that i know are big pollution areas (like near industry or even when I can see wildfire smoke)
There are some that seem broken and someone needs to reach out to them.
I also feel broken ones shouldn’t read zero as that could be seen as good air quality.
One thing I suspect is that there are indoor sensors mistakenly labeled as outdoor sensors - I think that’s the default. I wonder if PurpleAir could detect at least cases where this happens by looking at the temperature being reported, and see whether it’s at least roughly tracking the outdoor temperatures at the time?