Vehicles make their way along a highway as fog covers most of Beijing on March. Thick fog and air pollution covered the city dropping to "hazardous" level in early March this year.
Visitors look out at the skyline clouded by pollution in Shanghai on May 15, 2012.
Girls wear face masks to protect against pollution in the streets of Beijing in December 2011.
Vehicles making their way along a road on a smoggy day in Beijing on January 18, 2011.
Chimneys of factories are seen in Guangzhou in November 16, 2010.
A man walks through heavy pollution on a street in Beijing on November 2011.