About 60 per cent of the SO2 emissions come from power stations in which coal is used. In North America, photochemical oxidants, sulphur oxides and nitrogen oxides are common air pollutants. During the last two decades only, the major cause of air pollution has shifted from SO2 to photochemical air pollutants. Well- documented cases of serious vegetation damage, caused by smog, ozone, peroxyacetyl nitrate (PAN), SO2, fluorides or ethylene, are already known (see Waste Management and Control, Natl. Acad.

Sci. USA. NRC Publ. No. 1400, p.

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127, 1966) and polluted air has been established as being responsible for adverse effects on forest yields. In the same publication (NRC No. 1400), “pollutants” are described as “the residues of things we make use of and throw away. As the earth becomes more and more crowded there is no longer “an away” ….

our whole economy is based on taking natural resources, converting them into things that are consumer products, selling them to consumers, and then forgetting about them. But there are no consumers—only users. The user employs the products, sometimes changes it in form, but he does not consume, he just discards it… One person’s trash basket is another person’s living space.” The atmosphere is one of the basic prerequisites for life on earth. It consists of several different layers of air that filter out harmful radiation from the sun.

Increasing quantities of air pollutants are now causing changes in the atmosphere. Through our emissions of CFCs and other compounds, mankind has disrupted the ozone balance in the stratosphere (15-50 km above our heads). For this reason, several countries have signed an agreement-the Montreal Protocol—to reduce and eventually eliminate emissions of sub­stances that destroy the ozone layer. The latest research findings indicate that the depletion of the earth’s ozone layer is proceeding at a faster rate than expected.