Pollution in Beijing

Italy's Camila Giorgi returns the ball to Russia's Svetlana Kuznetsova during the French tennis Open second round match at the Roland Garros stadium in Paris, France.

A teacher leads her students doing body exercise during class break in a classroom on a foggy day in Jinan, Shandong province, January 14, 2013. Heavy fog enveloped a large swathe of east and central China, with the city's residents being advised to stay

Cranes atop a residential building under construction in central Beijing, April 18, 2012.

Buildings and the Guomao Bridge are pictured amid heavy haze and smog in Beijing, October 29, 2011.

Visitors to Tiananmen Square shield themselves from the sun with umbrellas on a hot and hazy day, July 28, 2010.

Smoke billows from a chimney of a heating plant in Beijing, February 13, 2012.

A fã de futebol e acima de tudo fanática pela selecção brasileira, Marilza Guimarães da Silva, de 63 anos, posa para a foto com uma réplica do troféu do Mundial de Futebol, vestida numa das suas diversas indumentárias com as cores do Brasil. Brasília, Maio 27, 2014. REUTERS/Joedson Alves 

A coal-burning power station at night in Xiangfan, Hubei province, September 15, 2009.

Paramilitary policemen practice drills inside the Forbidden City amid haze in central Beijing, December 4, 2011.

Buildings in Beijing are pictured on a day with heavy haze and smog, October 28, 2011.