Pollutants are emitted into the atmosphere by both industrial and natural processes. Natural processes also remove these pollutants from the atmosphere, but when total emissions exceed the capacity of natural sinks, the quality of the air decreases. Air pollution can cause severe damage to plants, animals, and microorganisms. Air pollution can also cause subtle damage to the biosphere, as manifested by growth retardation, acceleration of aging processes, alterations in reproductive potential and genetic constitution, and alterations in host-parasite relations. However, air pollutants may serve some beneficial roles, such as satisfying some nutrient requirements of plants. Field studies, however, indicate that the environment, in general, is adversely affected by atmospheric pollution. Unfortunately, only speculations on ecologic ramifications of air pollution are possible with the present level of knowledge.