June 22, 2009

Ozone risks life

Scientific concern about the future of man's fragile environment has ranged from pollution of the oceans and the air to radioactive contamination in a nuclear war. Now researchers are turning their attention to the atmosphere's ozone layer, which protects all life below from a lethal overdose of the sun's ultraviolet light. Their ominous findings: the vital blanket of gas is so fragile that it might well be severely damaged or destroyed by large-scale atmospheric nuclear tests, to say nothing of military and civilian supersonic aircraft, and even the widespread use of aerosol sprays.

Ozone is a form of oxygen that has three instead of the usual two atoms of oxygen in each molecule of gas. It is formed when ordinary molecules of oxygen are ripped apart by radiation or discharges of electricity, and is most noticeable after a lightning storm, when it can be detected by its pungent smell. 
Most of the ozone in the air is concentrated in a layer some 15 to 30 miles above the earth, where it absorbs much of the sun's ultraviolet radiation. Trouble is, ozone is far from stable; it readily gives up one of its oxygen atoms to other gases and turns into ordinary oxygen, which does not block ultraviolet radiation.
Last week the vulnerability of the ozone layer was emphasized by two startling reports on the long-range effects of the propellant gases used in aerosol sprays. Writing in Science, University of Michigan Physicist Ralph Cicerone notes that spray-can gases, mostly chlorine compounds such as Freon, are highly stable under ordinary circumstances. 
Thus they are building up in the lower atmosphere and gradually rising toward the ozone layer. At that altitude, ultraviolet radiation breaks down Freon and the other chlorine-based gases, causing the release of chlorine atoms. They in turn react with ozone, converting it into ordinary oxygen.
Cicerone estimates that even if the use of aerosol sprays were halted immediately, the gases already in the atmosphere would cause a 10% reduction of ozone in the layer by 1990. That would result in a substantial increase of ultraviolet radiation on the earth, causing at the very least a greater incidence of skin cancer among humans. It might also disrupt the food chain by affecting food crops and plankton in the oceans. Lastly, the depletion of the ozone layer might have certain incalculable consequences like changing the earth's weather patterns.

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