Refinery Burn off
Yes, Wyoming has a lot of windmills... they also have a whole lot more oil wells(and coal mines) Here is a refinery by Casper burning off excess stuff. Mmmm black, sooty smoke in a clear blue sky... all of the soot is a sign of poor combustion. if the can get more oxygen in the mix is would burn more completely and have less soot... but what the heck... there's a lot of air out here to fill with the stuff.