BEIJING — A massive effort to clear up the skies over Beijing for the Olympics paid off with China's capital seeing its cleanest air in a decade, the city's environmental authority said today.

The Beijing Municipal Environmental Protection Bureau said the improvement in air pollution was mainly the result of special temporary measures that shut factories and banned cars from the roads for the Olympic Games.

The clear weather continued into September, with crisp blue skies offering a rare glimpse of Beijing's western hills normally obscured by smog.

The environmental bureau said in a notice on its Web site that the density of major pollutants was cut by 45 percent in August. It said there were 14 days with the best air quality, or level 1, and only one day rated at the worst quality, or level 3. Normally, some months have only a handful of days with level 1 air quality.

"This is the best quality in the past 10 years," the statement said, referring to the 45 percent reduction.

The city's air pollution was a major concern in the months leading up to the Olympics, but the worries largely evaporated as the games began under relative blue skies.

"Temporary measures to reduce pollution that were put in place in Beijing and surrounding provinces to guarantee clean air for the Olympics played a fundamental role in improving the air during the Olympic period," the bureau said.

Levels of major pollutants such as sulfur dioxide, carbon monoxide and nitrogen dioxide fell to levels normally found in cities in developed countries, it said. Beijing typically has air that is two to three times dirtier than in most Western countries.

City officials shut down scores of factories, stopped almost all construction and removed 2 million vehicles from the roads for a two-month period that will last from July until after the Paralympics end Sept. 17.