With the rapid development of urban

With the rapid development of urbanization, a large number of people gathered, high-rise buildings quickly, the city density increases, making the city air can not flow quickly, the natural air purification capacity is greatly weakened. Coupled with the large number of vehicles, aircraft and ships exhaust emissions, industrial emissions without treatment, the burning of garbage produced by toxic gases, residents in winter heating coal produced a large number of harmful gases, and so on, the problem of air pollution is more serious and has been paid more attention by the society.