No definite conclusions can be made whether smog causes lung cancer, or the damage to humans from prolonged exposure to smog. Further research and data are needed to study the link between lung cancer and air pollutants. However, I believe that air pollution can be effectively treated since society is now aware of the problem. It is difficult but necessary to balance environmental protection and economic development, and to faithfully implement policies and enforce the law.

Zhong Nanshan, a renowned respiratory expert

China's flight efficiency rate was 68 percent last year, lower than the 72 percent in 2013. Apart from climate factors, poor airspace management is a major reason for frequent flight delays, which must be reformed. Reforms to low-altitude airspace management will be carried out this year, and authorities will also maximize current air routes.

Li Jun, president of the China Air Transport Association

Beijing will do everything it can to control population growth and to keep the population below 23 million by 2020. A series of legal and economic measures will be carried out in the future to ensure that the goal is achieved.

Wang Anshun, mayor of Beijing