Looking at the layer "Air Quality" on my iOS weather app there seem to be large circular areas of air pollution outside of large cities.
What could be the cause for such phenomena?
I looked at the same region after one day. The blob near Reno seems to persist. The blob in Montana nearly disappeared.
I could not find any incident in Montana to explain the temporary blob.
The blob near Reno has a diameter of min. 50km and is located directly over Yerington. The only incident I found in this area was on October 27. There was a car crash which could/should not be the cause for this.
The source of the weather app is linked to this: https://air.plumelabs.com/en/
Here the Plume Index is shown and the blob near Reno is clearly visible.