I remember the terrible smogs in the early fifties in West London. You literally couldn't see a hand in front of your face, and the sulphur in the air made it a sickly yellow colour. In those days, everyone burned coal to heat their houses.
My mother tied a man's hanky round our mouths and noses, and as you say Raggytash, on arriving at school it was black. We coughed and choked, but found it immensely exciting.

Isn't the pollution nowadays mostly from car exhausts?

Here in Norfolk we're plagued by those accursed wood burners. They're very popular here, and two different neighbours bring home huge bits of wood, old pallets, fencing panels and other stuff on their tractor trailers. They cut them up in their respective front yards, and the filthy smoke pours out of their bungalow chimneys in winter. We have to keep our windows shut if the wind is westerly (happens often)