Smog.

As I enjoyed one of my morning walks, I noticed there was not a bit of wind. Everything around me was very quiet and perfectly still. There wasn’t a rustle of leaves, I didn’t hear birds, it was just very quiet. I glanced to the west and noticed the air over Tucson was perfectly still as well. This was evidenced by the smog layer that had settled over the city. It formed a perfectly straight line across the entire metro area.