The government has shut schools, restricted road traffic and urged people to stay indoors as 24 cities across northeast China were put on “red alert” for extreme smog on Tuesday.
  China's most severe bout of air pollution this year has hit 460m people, who are exposed to smog levels six times higher than the World Health Organisation’s  daily guidelines, according to calculations by Greenpeace. The smog has lasted over three days in many areas.
  As of 11am local time, 217 flights at Beijing Capital Airport had been canceled — almost a third of the total scheduled for the whole day.
  China’s smog is worst in the winter, when households consume more electricity from coal-fired power plants, and municipal heating is turned on.