I just launched a non-profit, part of is it high quality air quality monitoring for Gary, IN. I'm looking to install it at/near the nearest residential area near USS Gary Works.
I've only been able to afford a 3 month rental of AQMesh's sensor, hopefully it'll trigger enough interest to get a few of these bad boys around Gary/Chicagoland.
Chicago used to be (and somewhat still is) an industrial and transportation hub. A substantial amount of metals and chemical industry still operates there.
Pennsylvania has a bunch of metal processing industries. Given Pittsburgh's reputation for steel production, that makes sense too.
Looks like a big blend of different industries in Chicago. That one I can't explain.