While students in Hainan are quite used to clear skies, Beijing teenagers are not so  lucky. As another warm winter approaches, the city can expect the normal clouds of smoke  caused by air pollution.      But things could start to get better soon. The government is co-operating with a US- based environmental protection agency to update existing buses and trucks with clean fuel  technology. The new technology could reduce air pollutants in existing diesel vehicles ( ) by 40 per cent. The programme will begin by testing buses in Beijing to see if the  technology can be applied to them.      "We encourage the development of public transportation. But at the same time we need  to reduce pollution from them," said an official.      Efforts are being made to improve the capital's environment with tighter controls on  emissions  . Some heavily polluting factories and construction sites, such as those  owned by the steel giant Shougang Group, have been asked to cut production in November  and December or be closed. Beijing was the third polluted city in the world at the end of  last century, according to the UN. But thanks to recent measures, the capital has made  some progress. Last year 224 clear days were rated as having good air quality. In 1998  the air quality index   gave just 100 days as good.      "I am glad to see an improvement," said a Senior 1 boy living in the northwest of  Beijing. "Compared to other places, the air quality of Beijing is still worrying though. I hate the pollution. Once I was riding my bike in the morning when I almost had a traffic accident because I couldn't see a car only metres away from me in frog."      In early October, the skies were covered by such a thick fog that a display show by  the visiting French air force was called off.      Rapid development, industry, traffic fumes   and sandstorms from the desert all  contribute to the city's bad air. The passage is mainly about   _  ?
a programme to improve Beijing's air quality progress made in Beijing's air quality Beijing's air pollution the difference between Hainan and Beijing