A series of photo pairings --- smog in London then, and in China now.
Above left, a woman in Changchun, China walks along a road on Oct. 21, in a dense smog that forced business, school, and road closures. On the right, a woman in London wears a protective mask in Nov. 1953 during a smog episode nearly a year after the city's deadly Great Smog.
Above left, a Chinese security guard stands amid dense smog at the pavillion on Coal Hill in Jingshan Park, Beijing, on Jan. 10, 2009. On the right, a British police officer wears a face mask while standing in a road in London in 1952.
Above top, a man wears a face mask aboard a subway car while commuting in Beijing on Jan. 23. Below, commuters trying to escape traffic caused by smog wait for the London Underground on a subway platform obscured by haze on Dec. 8, 1952.