A man walks through heavy pollution on a street in Beijing, China, on November 1. Air pollution in Beijing reached "hazardous" levels, the US embassy said, as thick smog blanketed the city for the fourth day running, forcing the closure of highways and cancellation of flights.

A blanket of haze hangs over the Hong Kong skyline early on April 3. A survey released at the end of 2010 by public policy think tank Civic Exchange found one-quarter of residents would like to leave Hong Kong to escape its pollution after levels reached a record high, prompting government warnings to people to avoid going out.

A child who was diagnosed with having excessive lead in his blood cries as he receives medical treatment at a hospital in Hefei, Anhui province in China on January 6, 2011.

Vehicles drive on Three Ring Road and Jianwai Street during rush hour in central Beijing, on Thursday, Dec. 23. Starting in 2011, Beijing will limit how many new cars it licenses to 240,000 annually, in an effort to ease the capital city's traffic jams.

A boy swims in the polluted waters of the river Sabarmati to dive for offerings that are thrown in by worshippers in the western Indian city of Ahmedabad on Aug. 20, 2010. In recent years, the religious festivals and customs in India have come under increasing scrutiny as public awareness of environmental issues grows.

A man walks on the beach where oil washes ashore from the Deepwater Horizon oil spill in the Gulf of Mexico on June 26, 2010 in Orange Beach, Ala. Millions of gallons of oil have spilled into the Gulf since the April 20 explosion on the drilling platform.