The massive effort to clear the skies over Beijing for the Summer Olympics paid off, the city's environmental authority said Monday, with the capital seeing its cleanest air in a decade. The Beijing Municipal Environmental Protection Bureau said the improvement in air pollution was mainly the result of special, and temporary, measures that closed factories and banned cars from the roads during the Games. The clear weather continued into September, with clear blue skies that allowed a rare glimpse of Beijing's western hills, which are normally obscured by smog. The bureau said in a notice on its Web site that the density of major pollutants was cut 45 percent in August.