Beijing saw 146 "blue sky days" during the first half of the year, which means the city's residents breathed in the least amount of pollutant in nine years, an environment official said Tuesday.

The blue sky days so far this year was 23 days more than the corresponding period last year and 47 days than the average level in recent years, said Du Shaozhong, deputy chief of Beijing municipal environmental protection bureau.

In June, Beijing saw 25 days, or 83.3 percent of the total, with blue skies, which was the best among the corresponding months since 2000.

Air quality in January, March, April, May and June this year are all better than corresponding months in the last decade, Du said.

Beijing has a five-grade classification of air quality: a reading below 50 is "excellent;" from 51 to 100 "fairly good;" 101to 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.

Environmental protection experts attributed the improvement of air quality to the reduced emission of pollutants and the after effect of measures taken during the Beijing 2008 Olympic Games.

The amount of pollutants related to vehicle emissions has not grown so far this year although the city has registered 200,000 more vehicles, because 55,000 heavy polluting vehicles were phased out.

Sandstorms during spring decreased from last year's 11 to this year's 6, which also benefited Beijing's blue sky drive.