More than 10 percent of China's land area has been shrouded in thick smog for the past few days, with the level of PM2.5 (particulate matter with a diameter of 2.5 micrometers or less and very harmful to humans) frequently exceeding the danger level in many cities.

Recent meteorological conditions such as temperature inversion, high humidity and low wind speed could be blamed for the smog. But in the final analysis, excessive consumption of coal and the high rate of emissions are the key causes of air pollution.

China is the largest consumer of coal. Coal makes up 70 percent of its energy structure. In 2000, the country consumed 1.4 billion tons of coal. By 2012, that figure had increased by 152 percent to more than 3.5 billion tons, or half of the global consumption. The burning of coal - intense in the power generation, steel and cement industries - is the primary source of air pollution in China, making it the top emitter in the world. Latest data show that coal burning accounts for nearly 90 percent of the sulfur dioxide discharge, and about 70 percent of nitrogen oxides and smoke.