BEIJING - Thick smog that has lingered over much of north China since last week is expected to disperse on Tuesday night as a cold front arrives.

According to the Beijing Meteorological Service, cold air will approach the Chinese capital's neighboring province Hebei on Tuesday night and help clear the smog in the region as it moves eastward.

Increased use of coal for heating during winter has been the main factor behind surging levels of PM 2.5, airborne particles that measure less than 2.5 microns in diameter and are especially harmful to human health, said the Beijing Municipal Environmental Monitoring Center.

An unfortunate combination of weather conditions has also helped trap pollutants, according to meteorologists -- cold air closer to the ground resulting from thawing snow reduced the mobility of airborne pollutants. The smog worsened in North China on Monday and the meteorological center upgraded its alert from yellow to orange, the second most serious level.

Visibility has been significantly reduced, causing traffic jams on some inter-city expressways and forcing closures on others.