We don't have smog around here, but I remember when I was a kid, there was a huge tire fire in Quebec this one time (I forget if it was a dump or a tire factory), and when the thick smoke made its way over here, the sky was dark and the daylight had an orange tint to it for a few days. This post reminded of that.
Yeah. I think this was something similar. Not stuff burning, but byproduct of the pollutants.