Participants run at the Bund near the Huangpu River as they compete in the Shanghai International Marathon December 1, 2013.[Photo/Agencies]

Participants run at the Bund near the Huangpu River as they compete in the Shanghai International Marathon December 1, 2013.[Photo/Agencies]

A participant wears a costume while competing in the Shanghai International Marathon December 1, 2013. [Photo/Agencies]

A participant wears a face mask as he competes in the Shanghai International Marathon December 1, 2013. According to the US consulate air quality readings, which measure PM2.5 particulates, Shanghai's air quality was "very unhealthy" on Sunday. [Photo/Agencies]

A kid runs next to participants as they compete in the Shanghai International Marathon December 1, 2013. [Photo/Agencies]