Five days in February failed to meet a required air quality standard of national grade II in Beijing due to holiday fireworks and the weather, an official with Beijing Environmental Protection Bureau said Monday.

Beijing uses a five-grade classification for air quality, with Grade I being the best and Grade V the worst. Days with Grade I and II air quality are regarded as blue sky days.

A total of 23 days in February met the required air quality standard, 5.5 days more than the average of the last ten years, but one day fewer than that of last year, according to the environmental protection bureau.

Experts said the main cause of the air pollution was the large amount of fireworks set off on Feb.13 and 14, when the eve and Chinese Lunar New Year fell this year.