BEIJING (AP) – Thick, gray smog fell over Beijing on Tuesday, 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.

Members of the public closely watch levels of PM2.5, particles measuring 2.5 microns across that are easily inhaled and damage lung tissue. The World Health Organization designates the safe level for the tiny, poisonous particles at 25 micrograms per cubic meter. 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.

State media reported that 169 flights have been canceled at Beijing Capital International Airport, where visibility fell at one point to 300 meters (984 feet). Sections of Beijing’s sixth ring road, the outermost highway encircling the city of more than 20 million people, were shut down in a bid to keep cars off the roads…. read more here