A recently study found people's lives are made shorter in North China. It is showed the life expectancy  had been cut down by 5.5 years there. Researchers think that the heavy air pollution in China should be to blame . It's really the truth. Our government has already done something. However, it doesn't seem to work so well. "Air pollution in China is doing harm to people's health. The harm is much more serious than we can imagine," said Chen Yuyu of Beijing University, one of researchers of this study. Dirty air brings serious problems in North China. In January this year, the air pollution was worse than that in other places. That was caused by rising temperature and waste gas  from coal heating. Chinese government should strongly fight against air pollution. They should think of more proper ways to deal with the problem. People should be encouraged to take buses, ride bicycles or walk, instead of driving cars. The factories that pollute heavily should be closed. "We need to improve our environment, although it might be expensive. Protecting our environment means protecting ourselves," Li Hongbin, another researcher of the study said. What's the main idea of the passage?
Air pollution in North China is caused by waste gas. To save the environment, our government should do something more. The temperature becomes higher and higher in North China. How air pollution in North China is caused.