You know how it is. You are looking at a couple of the 1500 or so photos that are still stored on a SD card in your digital camera and you come across some pictures you took months ago and you see something you haven't seen in a while.
We live in an amazing place, geographically speaking. We have mountains and valleys, rolling hills and high plains. When the temperatures dive in the winter pollution gets trapped between the ranges and the air gets dirty. It's called an inversion.
I've heard that this phenomenon occurred even before civilization came to the area, that the native Americans told settlers that in winters the whole area was covered with fog and bad air. I haven't researched this, but it doesn't really matter. It's bad now. Finding these pictures reminds me of how things were, and how they will be again. We've just got to be patient.