TO GO WITH China-economy-environment-coal-climate,FOCUS by Tom HANCOCK In this photo taken on November 19, 2015 (AFP)

TO GO WITH China-economy-environment-coal-climate,FOCUS by Tom HANCOCK In this photo taken on November 19, 2015, (AFP)

This picture taken on December 8, 2015 shows a billboard broadcasting advertisement outside a building (AFP)

Vehicles using lights travel on a bridge amid heavy smog after the city issued its first ever "red alert" for air pollution, in Beijing, China, December 8, 2015. (Reuters)

A building and a large screen are seen through thick smog in Beijing December 8, 2015 as China's capital issues its first ever "red alert" for pollution. (Reuters)

People drive along a highway on a polluted day in Beijing on December 9, 2015. Pollution red alerts spread to more Chinese (AFP)

This picture taken on December 8, 2015 shows birds flying across a street amid heavy smog in Beijing. Half of Beijing's private cars were ordered off the streets on December 8 (AFP)

An ambulance (top C) drives along an overpass amid heavy air pollution in Beijing on December 8, 2015 (AFP)

A woman wears a mask for protection against the pollution in Beijing, China, Wednesday, Dec. 9, 2015 (AP)