The `haziness index' is off the scale (relative to the two photos below). However, this is due not to increased pollution (*), but mostly to the fact that the Park Service's photos are not calibrated for time-of-day, and that they thus implicitly assume all scattering to be due to Rayleigh particles. This assumption breaks down near dawn & dusk, where the observed phase angle can approach 180 degrees. I am an expert in this are of light-scattering, and I recommend they read my paper on light scattering by small particles in Jupiter's ring for tips on how to properly interpret their images.

(*) I understand it was due on this day in part to severe forest fires in Russia (!).