Air pollution is one of the hottest topics at present because poor air quality is an important factor in both the incidence and cause of respiratory(呼吸道) diseases. Zhong Nanshan, a deputy to the NPC and a member of the CAE, said recently when the concentration of PM2.5 rises by 10 micrograms per cubic meter, hospitalization may rise by as much as 3.1 percent. Meanwhile, when the concentration of PM2.5 rises from 25 mgs per cubic meter to 200, the average daily death rate may rise to 11 percent. Zhi Xiuyi, a leading expert in lung cancer treatment and also vice-president of the CATS, said medical authorities used to focus on tobacco control as a primary means of preventing lung cancer. "But in fact, air pollution is no less harmful than smoking and our research team released a report earlier this year showing that the cancer rate in Beijing is closely related to industrialization," he said. The report, conducted by the Beijing Institute of Cancer Research, shows that the number of cancer patients in China has increased markedly during the past ten years. Chaoyang District, the city's main area of industrialization, has the highest incidence of cancer, almost double that of Yanqing, an area on the outskirts of the city. About four out of 1000 Chaoyang residents have some form of the disease, with lung cancer at the top of the list. "The risk of having cancer largely depends on the length of exposure and the concentration of noxious gases(有毒气体的浓度)," said Zhi. In response to the doubt whether seven years' exposure to poor air quality will almost result in cancer, Zhi said the time scale was taken from research overseas that suggested the rate of incidence generally peaked in the seventh year of exposure to a heavily polluted environment. 小题1: What is the passage mainly about?
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