It was no pea souper, but a bit, enough to notice.
I was talking to a kindergartener at recess after the fog was long gone and trying to explain that fog is really a cloud lying on the ground. She kept looking at the ground, asking “where is it?”
The Nova Scotia setting and time travel element of this story appeal to me, but it would probably be a bit too leisurely of a read for most children these days. Greta travels back to Colonial times through the fog, and while I would hesitate to call her forays into the past adventuresome, her experiences do force her to grow up. The ending is bit disappointing to most readers, but it was a 1943 Newbery honor book. Personally, I kind of miss the Nova Scotia fog (gratuitous picture follows), so I wouldn’t mind reading it again.