According to a report from the municipal weather forecast bureau that was released on Monday, Beijing's air quality was rated "polluted" for ten out of 28 days in February, with the rating for one day reaching the "worst polluted" category.

Weaker winds, a rise in moisture, and the occurrence of a temperature inversion has caused thick haze to linger over Beijing's sky since February 16, a spokesman with the weather forecast bureau said.

The spokesman said that pollutants were more likely to accumulate and less likely to disperse under such conditions. Air quality was rated at the highest level of the index's pollution reading on February 21, prompting authorities to advise residents to reduce outdoor activities.

Though polluting factories had been moved from the city, an increase in the number of cars held back the city's fight against pollution.

A "blue sky days" target has been in use to keep the mega-city's air pollution under close watch. Authorities are aiming for 274 "blue sky days" this year, or only one quarter of the year being rated "polluted."