Ozone-Depleting Substances: Alternatives

Surrounding the earth at a height of about 25 kilometers is the stratosphere, rich in ozone, which prevents the sun’s harmful ultraviolet (UV-B) rays from reaching the earth. UV-B rays have an adverse effect on all living organisms, including marine life, crops, animals and birds, and humans. In humans, UV-B is known to affect the immune system; to cause skin cancer, eye damage, and cataracts; and to increase susceptibility to infectious diseases such as malaria. In 1974, it was hypothesized that chlorinated compounds were able to persist in the atmosphere long enough to reach the stratosphere, where solar radiation would break up the molecules and release chlorine atoms that would destroy the ozone. Mounting evidence and the discovery of the Antarctic ozone hole in 1985 led to the global program to control chlorofluorocarbons (CFCs) and other ozone-destroying chemicals. In addition to Antarctica, ozone loss is now present over New Zealand, Australia, southern Argentina and Chile, North America, Europe, and Russia. The ozone-depleting chemicals or substances (ODSs) of concern are CFCs, halons, methyl chloroform (1,1,1,-trichloroethane; MCF), carbon tetrachloride (CTC), hydrochlorofluorocarbons (HCFCs), and methyl bromide. The ozone depletion potential (ODP) for these chemicals is shown in Table 1. CFC-11 was assigned an ODP of 1.0; all other chemicals have an ODP relative to that of CFC-11. An ODP higher than 1.0 means that the chemical has a greater ability than CFC-11 to destroy the ozone layer; an ODP lower than 1.0 means that the chemical’s ability to destroy the ozone layer is less than that of CFC-11. In September 1987, the Montreal Protocol on Substances That Deplete the Ozone Layer (the Protocol) was signed by 25 nations and the European Community. The Protocol was the first Ozone-Depleting Substances: Alternatives