People usually check whether their keys, wallets and phones are with them before going out . But many people in China now have one more important thing to take -- a face mask  . They hope that it can protect them from polluted air. Since January, many cities in China have seen a lot of foggy days.In Beijing, only five days in January were free of smog . It is dirty air that looks like a mixture  of fog and smoke caused mainly by smoke from cars and factories in cities. Poor air has done harm to people's health, especially for children and old people. They fall ill easily and the hospitals are full of the the patients of respiratory   problems. To respond to the air  problems, the Chinese government and many Chinese people have  started to take action. Beijing announced plans to use cle an fuel in government vehicles and plant trees. It also asked citizens to set off fewer fireworks for celebrations. Three students from No.4 High School in Beijing wrote a report to advise how to fight the air pollution. They suggested that cars with large emissions  should not be allowed to use and factories should be closely watched. We hope more people will join us in making a difference. With all our efforts , the blue skies will certainly return for good. What are the main factors for PM2.5 according to the Chinese Academy of Sciences?
driving cars and having fewer trees burning coal and having fewer trees having fewer trees and no rain driving cars and burning coal