I remember those pea-soupers in London. I loved them - they had a particularly disgusting smell, but you couldn't see your own hand stretched out, and the sounds of the streets were amplified. It was also very strange how the fog swirled around outside, but did not really have much effect indoors. I remember standing by the front door at my granny's house, with it wide open, to try to get the fog to come in and fill all the rooms up, but it didn't. I was just a small girl then, but have clear memories of the smog.
I wanted to say how astonishing I find it that mostly (unless you are up in the mountains) clouds start at such a convenient height above the ground. They contain so much water. They weigh thousands of tons. It is a pretty amazing thing that they don't come crashing down. And if clouds usually 'lived' on the ground, presumably animal life would never have bothered to develop eyes, as we would all have been living in a permanent fog. (This is setting sunny days aside, of course). Nations would not have emerged, as we would have had a completely different view of territory. I am not a religious person, but I do think this is a miraculous whim of whoever or whatever created us. All of life would have been completely different.