A woman wears a face mask as she rides her bicycle past bare trees in central Beijing January 2, 2008. China has introduced cleaner fuel standards in its capital Beijing, its latest effort to curb the city's notorious pollution ahead of the Olympic Games in August. Under the new standards, authorities are hoping to cut emissions of acid rain-causing sulphur dioxide by 1,840 tonnes, official media reported citing Beijing's Environmental Protection Bureau. REUTERS/David Gray (CHINA)