Stratospheric Ozone Depletion
Ozone naturally occurs in the stratosphere (the higher layers of the earth's atmosphere) by the action of ultraviolet light from the sun on oxygen molecules. At this level, ozone has beneficial effects on health, in that it helps to filter out harmful ultraviolet rays that can cause skin cancers. Evidence suggests that stratospheric ozone depletion is being caused by man made emissions of chlorine and bromine-containing substances (halocarbons) such as: CFCs, halons, and HCFCs. HCFCs are similar to CFCs but have a lower potential for depleting ozone and in some cases are being used as transitional replacements. Emissions of methyl chloroform, carbon tetrachloride and methyl bromide also contribute to the effect.