Atmosphere

The gaseous covering enclosing the earth made up to the troposphere (up to a height of 10 km) and the stratosphere (from 10 km to 50 km). The unpolluted air in the troposphere consist of about 78 % nitrogen, 19 % oxygen, 2 % water vapor and a series of trace gases (neon, helium, etc.).

Air pollution 'which reaches the atmosphere is able to remain there, to be transported over great distances, and to be converted in chemical processes to form other, to some extent even more hazardous substances (e.g. the formation of Photo-oxidants from Oxides of Nitrogen and Hydrocarbons under the effect of sunlight). The composition of the atmosphere has changed during the course of the history of the earth. Problems appear to be associated with the fact that the atmosphere has undergone major changes since the start of the industrial revolution. These changes are brought about, e.g., by the Emission of gases which change the climate or destroy the ozone layer (Ozone Theory), as well as by changes in the biosphere (e.g. the destruction of the tropical rain forests).

> Chlorofluorocarbons, Climatic Changes, World-wide Environmental Pollution