BEIJING -- Beijing recorded 46 days of heavy pollution during 2015, accounting for 12.6 percent of the year, the Ministry of Environmental Protection (MEP) announced on Tuesday.

November and December saw 22 days of heavy pollution in Beijing due to winter heating, the MEP said, adding the city also recorded 186 days of air quality "up to par" during 2015, 14 days more than the year before.

The annual average density of PM 2.5 in Beijing, particulate matter that causes hazardous smog, stood at 80.6 micrograms per cubic meter, a year-on-year decrease of 6.2 percent.

Thirteen cities under surveillance in the Beijing-Tianjin-Hebei region had air quality "up to par" in 52.4 percent of days last year, a year-on-year increase of 9.6 percentage points.

For the other two economic power houses, the Yangtze River Delta region enjoyed air quality "up to par" during 72.1 percent of days in 2015, and Peal River Delta region, 89.2 percent of days.

Luo Yi, an MEP official, said despite an across-the-board improvement, air pollution was serious during the winter heating season in north China, and the Beijing-Tianjin-Hebei region recorded high density of PM 2.5.

Luo said the ozone pollution has become increasingly prominent.