There is a plume of something in the air above Chicago today. I noticed it on the way in, as a whiteish (or less blue) western sky. I thought it might be the lake breeze, but reasoned it would have been to the east towards the lake. Checking the satellite shows a plume moving to the southeast. It's probably smoke particulates from a wildfire somewhere, but the only recent one I've heard about is a set of fires not far from the parents' place in the Desert National Wildlife Refuge. From the direction of the plume I am guessing it must be a summertime fire from Northern Canada or Alaska, although the Alaska Fire report is only reporting 12 fires, one only 140 acres in extent. I see the Las Vegas Review-Journal is reporting a fire on the Nevada Test Site today.
UPDATE: Probably this fire.