坚持每天晨炼的人们,或小跑于大衔上,或漫步于河边、湖畔,或聚集于公园里打太极拳、跳迪斯科等。然而,却几乎无人注意,他们从中究竟获得了多少清新的空气。众所周知,清新空气富含氧气,而植物只有在阳光下方可进行光合作用,吸收二氧化碳,放出氧气,夜间的植物则吸收氧气,放出二氧化碳。从这个角度上看,夜间空气不如白天清新,清晨与晚上的空气也不如中午清新。又因在工业发达的现今,工厂烟尘、废气及机动车尾气等大量排放,使空气中含有大量二氧化碳、一氧化碳、二氧化硫等有害气体。又由于夜间往往少风,使有害气体累积于城市上空的低层大气 Persist in daily morning refining people, or trot on the title, or walk in the riverside, lakeside, or gathered in the park to play tai chi, dance disco and so on. However, almost no one noticed how much fresh air they got from it. As we all know, the fresh air is rich in oxygen, while plants can only carry out photosynthesis in the sun, absorb carbon dioxide, release oxygen, night plants absorb oxygen, emit carbon dioxide. From this perspective, the nighttime air is not as fresh as the daytime, and the air in the early morning and evening is not as fresh at noon. Due to the large amount of carbon dioxide, carbon monoxide, sulfur dioxide and other harmful gases contained in the air due to the massive discharge of industrial fumes, factory fumes, exhaust gas and vehicle exhaust, And because there are often less winds at night, harmful gases accumulate in the lower atmosphere above the city