Despite an 11-year improvement in air quality, officials from the Beijing municipal environmental protection bureau said the chain might be broken this year because of a booming economy and mounting numbers of cars.

In the recently-released Beijing Environmental Statement 2009, last year's eco-environment was rated "good" by the city's environmental protection bureau.

Statistics from the bureau show the city had a record 285 blue-sky days, about 78 percent of the whole year, which is 11 days more than in 2008.