The CCTV Tower, center, the headquarters of China Central Television, and other skyscrapers and high-rise office buildings are seen vaguely in heavy smog in CBD (Central Business District) in Beijing, China, 20 December 2016. Thick, gray smog fell over Beijing on Tuesday (20 December 2016), choking China's capital in a haze that spurred authorities to cancel flights and close some highways in emergency measures to cut down on air pollution. Beijing and much of industrial northern China are in the midst of a "red alert, " the highest level in China's four-tiered pollution warning system. The alert has affected 460 million people, according to Greenpeace East Asia, which calculated that about 200 million people were living in areas that had experienced levels of air pollution more than 10 times above the guideline set by the World Health Organization. On Tuesday morning, the PM2.5 reading in Beijing climbed above 300. In many northern Chinese cities, the reading has exceeded 500 micrograms per cubic meter.
