[morgosmaci]

All of the US cities in the North America top 50 are rural CA cities. I have to assume that their over all badness last year was due to the fires.

[codyb]

I think it’s actually the agricultural centers. When I visited NAPA valley when I was younger you could see the smog blanketing the area. Not sure what exactly smogs up the air so foully there from the agricultural production but it seems to be a large contributor.

[mturmon]

Their monitoring in CA appears to be a lot denser than in (say) the midwestern US. In general, agriculture creates a lot of dust. You can certainly see some hot spots in their CA data due to fires, e.g. the PM2.5 of 200+ in Paradise, CA.