Ann Martin Golden, age 15, of Stuttgart, Ark., for her question:
WHAT IS THE OZONE LAYER?
Ozone in the lower regions of the earth's atmosphere often helps to increase air pollution. In strong concentrations ozone can make a person's eyes smart and his nose run. It has even been responsible for killing plants.
Ozone sometimes builds up when sunlight acts on nitrogen oxides from automobile exhaust fumes. This excess ozone may contribute to pollution. Ozone is a form of oxygen. It has a sharp odor andcan often be noticed near electric switches and machinery, and also in the air after a thunderstorm.
Molecules of ordinary oxygen are made up of tw oxygen atoms joined tightly together. But ozone molecules have a third oxygen atom loosely attached to these two. The third atom can easily separate from the molecule and combine with other substances. Because of this, ozone is classified as a chemically active gas.
Every flash of lightning converts some oxygen into ozone. The gas is also formed by electric sparks, such as those from motors. Commercial ozone is made in a machine called an ozonizer.
When high energy radiation from the sun strikes oxygen in the earth's atmosphere, some of it is converted into ozone. On the average, air at ground level contains less than one part of ozone per million parts of air. But 15 miles above the ground there is a more concentrated layer of ozone.
The ozone layer high above the earth actually contains only about six parts of ozone per million parts of air, but this is enough to shield the earth from much of the sun's ultraviolet light. Ultraviolet rays harm living tissues. Without the protection of the ozone layer in our atmosphere, plants and animals probably couldn't live here on earth.
Some scientists say that the ozone layer can be destroyed by a group of chemical compounds called fluorocarbons. Fluorcarbons are widely used as propellants in aerosol spray cans.
After they are released from the cans, fluorcarbons slowly rise into the earth's atmosphere. There, the scientists say, they are broken up by the sun's ultraviolet rays and release chlorine atoms. These chlorine atoms react with other chemical substances in the atmosphere and may gradually reduce the ozone concentration.
If the ozone layer in the earth's atmosphere is greatly reduced, the earth would be exposed to increased amounts of harmful ultraviolet radiation. Because of this possible danger, various groups have been urging that the use of fluorocarbons be either greatly restricted or even prohibited.
Ozone was discovered in 1840 by a German chemist named Christian Friedrich Schonbein.