Hence the term "London Fog" which was not water.

"pea-souper" was a common term

Certainly, when I was a kid, a trip into London was an adventure. You knew when you were near the centre of town because the buildings were all coal black.

China uses the term "sea mist" to dupe tourists. It's not fooling anyone, though...

Yeah, I saw a ton of sea mist in Wuhan when I visited.

No kidding? I always understood London to have absolutely perfect conditions for real pea soup fog. Much like San Francisco.