Hazardous smog over Beijing

A pedestrian wears a mask at Tiananmen Square as protection from severe pollution on Thursday, January 31, 2013, in Beijing. It's the fourth time this year that a heavy blanket of smog has affected eastern China, including the capital. The air quality has reached hazardous levels, and residents were encouraged to avoid outdoor activities. <a href='http://edition.cnn.com/video/#/video/world/2013/01/31/mr-beijing-smog.cnn
' target='_blank'>Watch a video explaining the hazardous smog.</a>

A pedestrian wears a mask at Tiananmen Square as protection from severe pollution on Thursday, January 31, 2013, in Beijing. It's the fourth time this year that a heavy blanket of smog has affected eastern China, including the capital. The air quality has reached hazardous levels, and residents were encouraged to avoid outdoor activities. Watch a video explaining the hazardous smog.