Article Photos: Smog thick enough to cancel flights hits Beijing 4/4

Chinese security personnel march in thick haze near the portrait of former Chinese leader Mao Zedong in Beijing Tuesday, Jan. 29, 2013. Extremely high pollution levels shrouded eastern China for the second time in about two weeks Tuesday, forcing airlines in Beijing and elsewhere to cancel flights because of poor visibility and prompting government warnings for residents to stay indoors. (AP Photo/Ng Han Guan)