Smog hits north, fog settles in southeast

Hebei province is seeing the most serious air pollution since the onset of winter weather, with the density of pollutants soaring to a high level, the province's air monitors said on Tuesday.

This round of air pollution began on Friday and is expected to end on Monday, lingering longer than the previous three rounds since October, according to the Hebei Environmental Emergency and Heavy Pollution Warning Center.

Locked in by a stable atmosphere, high humidity and a temperature inversion, air pollutants have accumulated. The density of PM2.5 - hazardous particulate matter smaller than 2.5 microns in diameter - increased gradually, it said.