The city government said on Tuesday that the strictest emergency measures would take effect when the pollution index for fine particulate matter was forecast to exceed 300 micrograms per cubic meter for three days running.
The emergency measures apply only to industries and individuals in Beijing, despite the fact that as much as 60 percent of the city's air pollution wafts in from neighboring provinces, such as Hebei to the south.
In north China, meanwhile, visibility shrank to less than half a football field and small-particle pollution soared to a record 40 times higher than an international safety standard as the region entered its high-smog season.
BA/BA