Some of the Chinese capital's 22.5 million residents have turned to humor to cope with persistent toxic air that once again soared above hazardous levels on Tuesday.

A joke circulating among Chinese journalists told of a reporter approaching an old woman on the street to ask about the impact of the smog. "The impact is huge," the woman replies. "First of all, I'm your uncle."

Some users of social media traced the shapes of famous Beijing landmarks on photographs in which the buildings were nearly obscured by the smog and posted them online.