Great Smog of London

In 5 December 1952, a great smog took over London.

The Tenth Doctor and Donna Noble were in the city when the event happened, and got lost in the smog. (AUDIO: The Creeping Death)

Behind the scenes
Though the name "Great Smog of London" is never used in the story, the date in which the story is set and the Doctor's comment that the smog happening was the worst London had ever seen make the event recognisable enough.