Beijing's education authorities ordered all of the city's primary and middle school students indoors as China's weather observatory issued smog alerts for the country's northern regions on Sunday.
All elementary and middle schools, kindergartens and extracurricular training schools should cease outdoor activities from Monday to Wednesday, the Xinhua news agency reported on Sunday.
Beijing made global headlines last week during the Paris climate change talks when its air quality went "beyond index" with a PM2.5 - particulate matter 2.5 microns and smaller - reading of 678 micrograms per cubic metre near Tiananmen Square. The World Health Organization safe recommendation is 25.
PM2.5 pollution penetrates the lungs and can trigger heart attacks, stroke, lung cancer and asthma.
In response last week the government issued the same "orange" alert, its second-highest warning on a four-colour scale, and advised all elderly and children stay indoors.
Beijing may struggle to clean up its air in time for the 2022 Olympics as the sources of its air pollution are not local, according to US researchers.
The capital city "receives much of its pollution from distant industrial areas, particularly Shijiazhuang, [322 kilometres] to the south-west," Robert Rohde said in a press release for his research released in August this year.
Bad air contributed to 1.6 million deaths a year or roughly 17 per cent of all deaths in China, Rohde and co-author Richard Muller outlined in the science journal PLOS One.
Air pollution kills about 4,000 Chinese people a day, with coal burning a key contributor, according to the scientific paper published by independent research group Berkeley Earth.
The smog will dissipate by Thursday, the National Meteorological Centre said.
Saturday, December 17, 2016 - 13:08