Fifteen miles above the ground, a three-millimeter thick layer of gas encircles the earth. Although this layer is hardly thicker than the diameter of a pencil lead, it protects the earth from dangerous ultraviolet (UV) radiation. UV radiation promotes human skin cancers and cataracts, and depresses the human immune system. UV-B, a form of UV radiation, decreases the potency of natural killer cells that destroy cancers and viruses. UV-B also triggers the production of cells that suppress some defense mechanisms in the human immune system. However, this layer, usually known as the ozone layer because it consists of gaseous ozone, is being destroyed as you read.

You see, chlorofluorocarbons (CGCs), halons, and other human-made chemicals are released from things such as Styrofoam, air conditioners, and fire extinguishers. When the gases enter the stratosphere,the level of the atmosphere about six to thirty miles above ground,the sun's radiation breaks them down, releasing chlorine atoms that destroy ozone molecules. Just one chlorine atom will destroy a hundred thousand ozone molecules before finally settling to the earth's surface. Roughly five percent of the ozone layer has already been destroyed by CFCs, and a hole in the ozone layer has been discovered over Antarctica.

With the diminishing ozone layer, the earth receives increasing UV radiation. Along with promoting the health problems mentioned, the growing level of UV rays striking the earth will reduce crop yields and fish populations. UV-B radiation affects the photosynthesis and metabolism of plankton in the oceans, and causes mutations in some marine organisms as well as damaging the eggs of others. Also, UV-B rays cause cell and tissue damage in many crop plants. Some scientists believe ozone loss may even affect climate. They hypothesize that a loss of ozone in the stratosphere will cool that layer, possibly altering global wind patterns. Changing winds will change the weather in ways we can't predict.

Although most experts say that current ozone depletion is irreversible ,it will take the planet at least a hundred years to replenish the ozone , there are some things you can do to lessen the dangerous chemicals being released and to protect yourself. Don't buy halon fire extinguishers, and avoid using "foam" materials for packing or other purposes. Use packing materials such as shredded newspapers or plain popcorn. Be cautious with air conditioners: if your air conditioner breaks, get it fixed properly, since more refilling will allow CFCs contained in the coolant to leak into the air. Also, try to patronize repair shops that use CFC recycling equipment so the CFCs removed from your air conditioner aren't allowed to evaporate into the atmosphere. Do your best to avoid aerosol cans, since even though CFCs aren't contained as propellants, the substitute gases add to other environmental problems such as smog.

To protect yourself from UV, use a sunscreen of at least SPF 15, reapplied frequently, and stay out of the sun between 10 a.m. and 2 p.m., when UV radiation is at its mid-day high. However, since sunscreens don't protect against the damage to the human immune system by UV-B, your best protection would be to avoid extensive exposure to the sun.

Thankfully, steps are being taken to reduce ozone-depleting gases. For example, a 1990 treaty, signed by 61 countries, calls for an end to the production of CFCs by the year 2000. In the United States, use of CFCs in spray cans is already illegal. But remember, although the production of CFCs will be halted in the future, air conditioners and other machines using coolants may contain CFCs if they were manufactured before the CFC ban. Make sure you continue to take precautions even after CFC production is banned.

For more information, a good book to use is 50 Simple Things You Can Do to Save the Earth, which was reviewed in the November issue. 50 Simple Things... covers many environmental options so the information on any certain issue is brief. There are also more specialized books on ozone depletion which you can find at most bookstores and libraries. n