Combo photo taken on Jan. 23, 2013 (up) and Jan. 22, 2013 (bottom) show the tower of the Zhengyang Gate in Beijing, capital of China. The air quality hit the level of serious pollution in Beijing on Wednesday, as smog blanketed the city. (Xinhua/Wang Yueling)

A woman and a baby boy wearing masks are seen in fog-enveloped Beijing, capital of China, Jan. 23, 2013. The air quality hit the level of serious pollution in Beijing on Wednesday, as smog blanketed the city. (Xinhua/Luo Xiaoguang)