Chlorofluorocarbons and ozone depletion

Abstract

When viewed from space, Earth is remarkably beautiful, and, as we know, very hospitable to life. However, Earth's atmosphere is only a very, very thin layer covering the land and water surface. All of us who live on this surface must be grateful for the protection of this atmospheric layer which lies between us and the vacuum of outer space. Without it, life as we know it would not exist. Here, I shall talk about the changes which are occurring in this atmosphere, and especially about the very rapid pace for these changes during the last two decades. After many years as a laboratory chemist, I became an atmospheric scientist during the early 1970s. This change in direction was not a deliberate, abrupt change in the focus of our work, but rather began only as a minor sideline to my regular research pursuits. The transition started when I first learned of the 1971 experiments of the British scientist James Lovelock. He had earlier explored the composition of the atmosphere in preliminary experiments in Ireland with an instrument specially designed by him, the electron capture gas chromatograph, and found trace amounts of several previously undetected compounds including trichlorofluoromethane (CC1,F). He then placed the apparatus on a ship traveling from England to South America and on to Antarctica. In every air sample throughout the voyage, he found measurable quantities of CC1,F, as indicated by the circles in Figure 1. This chemical compound, often designated commercially as CFC-11, was obviously present everywhere throughout both the Northern and Southern Hemispheres. These observations presented me with an interesting but seemingly harmless scientific puzzle in 1972 and 1973: what will eventually happen to these man-made molecules which have been released into the atmosphere and now have spread globally? The chlorofluorocarbon (CFC) family of gases did not exist in nature, but was created by man because several of them possess physical and chemical qualities which make them technologically very useful. Their primary advantages were that they are chemically inert and were easily converted between the liquid and gaseous states at ordinary temperatures. The most important CFCs in 1990 are CFC-11, CFC-12 (CC12F2) and CFC-113 (CC₁₂FCCIF₂). The major uses of these CFCs are as propellant gases in aerosol sprays in the foaming of polymers for home insulation, automobile seat cushions, and countless other applications; as the refrigerant gas in home refrigerators and automobile air conditioners; and in the cleaning of electronic components. This versatility in the market-place brought a steadily increasing demand for the CFCs during the 1950s and 1960s, and they have become very common throughout all modern industrial societies, where numerous products made with CFCs are encountered daily. World-wide production doubled every five to seven years into the mid- 1970s, approaching one million tons per year by 1974. Furthermore, almost all of these uses share the additional characteristic that the CFC gases sooner or later are released into the atmosphere.