An environmental legacy of the twentieth century is the use of gaseous compounds called chlorofluorocarbons (CFCs, which are also known as Freon) in a variety of household and personal products. The escape of these compounds into the atmosphere has triggered the destruction of an atmospheric gas called ozone. The lessened ozone has led to an increase in the amount of cell damaging ultraviolet (UV) light reaching Earth’s surface. The increasing prevalence of skin ailments, including some cancers, has been linked to the increased amount of UV light. Beginning in the 1980s, the decrease in atmospheric ozone spurred international efforts to phase out the use of CFCs. The best-known example of this international resolve is the Montreal Protocol on Substances that Deplete the Ozone Layer, a treaty signed by 191 nations that took effect in 1989. The treaty, which has since been revised seven times, has established a timetable for phasing-out the use of several ozone-destroying compounds including CFCs.
The five main chemical formulations of CFCs that were developed in the 1930s proved to be popular in a variety of manufactured products since they were non-toxic, non-poisonous, non-flammable, and not prone to react with other compounds. Almost immediately, CFCs began to be used as a replacement for harmful compounds such as ammonia. Uses included application as a refrigeration coolant, cleaning solvent (particularly in electronic industry in cleaners for circuit boards), and as a propellant in spray cans and foam-emitting fire extinguishers. Over the next three decades, CFCs that were given off by the various products dissipated into the atmosphere. Until 1973, if an accumulation of CFCs in the atmosphere was thought of at all, it was dismissed as inconsequential. Then, scientists at the University of California, Irvine, discovered that CFCs persist for 20 to 100 years in the region of the atmosphere known as the stratosphere. They also proposed that this longevity could have adverse effects on the ozone constituent of the atmosphere. Subsequently, their view was confirmed. It was shown that the UV portion of the incoming sunlight can break the CFC molecule apart. The UV cleavage releases chlorine, and the free chlorine destroys ozone. Another type of hydrocarbon that contains bromine instead of chlorine is also destructive to ozone. Ozone is made up of three oxygen atoms. Its chemistry makes intact ozone capable of absorbing UV radiation, which reduces the amount of this portion of sunlight that reaches Earth’s surface. However, with the depletion of ozone from the stratosphere, the levels of UV radiation penetrating to the ground increased during the latter half of the twentieth century. The reason that this is a concern is because UV light is very energetic. The energy allows the light to penetrate into the top layers of skin and through the cells in these layers. The cells can be damaged on prolonged exposure to the sun. One example of the damage that can be caused is sunburn. More serious damage can result, since the energy in UV light is sufficient to break one or both of the strands of the double helix of genetic material (usually deoxyribonucleic acid, DNA) that is present inside most plant, animal, and human cells. Sometimes the damage can be repaired. However, sometimes this repair is not accomplished correctly. Alternately, the breakage of the genetic material can be too extensive to be completely fixed. The result can be a change (mutation) in the cells that survive. Although some changes are not serious, others are. For example, some mutations affect the genetic checks and balances that control the ability of cells to grow and divide. A consequence of this breakdown in normal cell processes can be uncontrolled growth and division of cells. Such cells are cancerous. Increased exposure to UV light has been linked with the increasing prevalence of several types of cancer. Furthermore, the long lifetime of CFCs means that even a free chlorine from one CFC compound can destroy ozone for decades. Concern over ozone depletion and the link between this depletion and the increased threat to health became urgent in the early 1980s when it was discovered that the atmosphere over Antarctica contained much less ozone than other regions. Satellite images of the near-depletion of Antarctic ozone—a phenomenon dubbed the ozone hole—galvanized the global community to take action to curb the release of CFCs into the atmosphere.
Following the widespread adoption of the Montreal Protocol, use of CFCs has declined. For example, in 1983 the global production of CFCs was more than 1.2 million tons. By 2004 global production had declined to 70,000 tons.
Books DiMento, Joseph F. C., and Pamela M. Doughman. Climate Change: What It Means for Us, Our Children, and Our Grandchildren. Boston: MIT Press, 2007. Gore, Al. An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It. New York: Rodale Books, 2006. Seinfeld, John H., and Spyros N. Pandis. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. New York: Wiley Interscience, 2006.