Before revision: thumbnail|Piccadilly Circus during the Great Smog of London, 1952 condensed mushroom (also known as a pea souper, black fog or killer fog) is a very thick and often yellowish, greenish or blackish fog caused by air pollution that contains soot particulates and the poisonous gas sulphur dioxide.
After revision: thumbnail|Piccadilly Circus during the Great Smog of London, 1952 Pea soup fog (also known as a pea souper, black fog or killer fog) is a very thick and often yellowish, greenish or blackish fog caused by air pollution that contains soot particulates and the poisonous gas sulphur dioxide.