Beijing saw 73 "blue sky days", 81.1 percent of the total, in the first three months of 2009, Beijing authorities said on Tuesday.

The city experienced six more blue sky days than in the first quarter of last year, and 24.3 days more than the average of the last decade, said an official of the Beijing Municipal Environmental Protection Bureau.

Experts at the bureau said active cold air flows had helped particulate matter to disperse.

Efforts to reduce pollution from heating systems had paid off with January having the most blue sky days since 2000, said the official.

The bureau is aiming for a blue sky day rate of 71 percent this year.

Beijing has a five-grade classification of air quality: a reading below 50 is "excellent;" from 51 to 100 "fairly good;" 101 to 200 "slightly polluted;" 201 to 300 "poor;" and more than 301 "hazardous." Days with excellent or fairly good air quality are counted as blue sky days.

The number of blue sky days rose to 274 last year from 100 in 1998, when the capital launched the blue sky drive.

(Xinhua News Agency March 31, 2009)