Chlorofluorocarbons, potential

Trichloroethylene is being evaluated by the industry as a precursor in the production of hydrochlorofluorocarbons (HCEC), the replacement products for the chlorofluorocarbons impHcated in the depletion of the stratospheric ozone. At this time it is too early to project any estimates or probabihties for potential volume changes as a result of this opportunity (23). 

The other global environmental problem, stratospheric ozone depletion, was less controversial and more imminent. The U.S. Senate Committee Report supporting the Clean Air Act Amendments of 1990 states, Destruction of the ozone layer is caused primarily by the release into the atmosphere of chlorofluorocarbons (CFCs) and similar manufactured substances—persistent chemicals that rise into the stratosphere where they catalyze the destruction of stratospheric ozone. A decrease in stratospheric ozone will allow more ultraviolet (UV) radiation to reach Earth, resulting in increased rates of disease in humans, including increased incidence of skin cancer, cataracts, and, potentially, suppression of the immune system. Increased UV radiation has also been shown to damage crops and marine resources."... 

Another area of potential interest is in refrigerator liners. The move away from the ozone-layer-damaging chlorofluorocarbons (CFCs) to HCFCs in the USA and pentane/cyclopentane blends in Europe has not been without problems. These newer materials have an adverse effect on ABS whereas the nitrile resin appears satisfactory, if more expensive. 

The hazard identification step is perhaps the most important, because any hazard not identified will not be considered in the decision process. For example, the impact of chlorofluorocarbons on atmospheric ozone was unknown for much of the period of their use, and this potential hazard was not considered until recent years. 

The question of the fate of chlorofluorocarbons upon their release into the atmosphere IS of great interest at present because of the potential damage to the earth s protective ozone layer caused by the reaction of ozone with photochemically generated chlorine atoms... 

Unfortunately, the thermodynamically favored reactions of trichlo-rolluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12) with water do not proceed to a significant degree below 300 C and at least 200 atm (1 atm = 101.325 kPa) or greater [42] (equation 44) Even at 4000 atm randoimzation rather than complete hydrolysis occurs, leaving another chlorofluorocarbon, chlorotri-fluoromethane (CFC-13), which is also potentially harmful to the earth s ozone layer... 

The cap is the percentage of the calculated level of chlorofluorocarbons consumed in the base year plus the calculated level of hydrofluorocarbons consumed the same base year It applies only to HCFCs Calculated in the context means that the amount of each substance is adjusted by its ozone depletion potential (ODP), a measure of its potential to deplete stratosphenc ozone relative to that of CFC 11... 

Thus, the mean temperature of the atmosphere, which is about 20°C at sea level, falls steadily to about —55° at an altitude of 10 km and then rises to almost 0°C at 50 km before dropping steadily again to about —90° at 90 km. Concern was expressed in 1974 that interaction of ozone with man-made chlorofluorocarbons would deplete the equilibrium concentration of ozone with potentially disastrous consequences, and this was dramatically confirmed by the discovery of a seasonally recurring ozone hole above Antarctica in 1985. A less prominent ozone hole was subsequently detected above the Arctic Ocean. The detailed physical and chemical conditions required to generate these large seasonal depletions of ozone are extremely complex but the main features have now been elucidated (see p. 848). Several accounts of various aspects of the emerging story, and of the consequent international governmental actions to... 

Recognition of the threat of stratospheric ozone depletion posed by chlorofluorocarbons and chloro-fltiorohydrocarbons led 131 countries to sign the Montreal Protocol in 1987. Production of chlorofluorocarbons was banned as of January 1, 1996, because of their potential to further deplete stratospheric ozone. Chlorofluorohydrocarboiis will be... 

Hydrochlorofluorocarbon-141b, or 1,1-dichloro-l-fluoroethane (HCFC141b), has been developed as a replacement for fully halogenated chlorofluorocarbons because its residence time in the atmosphere is shorter, and its ozone depleting potential is lower than that of presently used chlorofluoro... 

Chlorofluorocarbons (CFCs) come in many forms, including those used as propellants for spray cans and for refrigeration (freon). They were banned as being potentially harmful to the ozone layer of the atmosphere. In 1987 an international agreement was signed by about 90 nations to reduce the use of CFCs by 50% by the year 2000. This did not seem adequate, so in 1990 a new treaty called for the elimination of the use of all CFCs by industrial nations. Some third world countries (e.g., China, India, Russia, and Mexico) still make and sell CFCs, some of which are smuggled into the United States. 

Over the past several decades, there has been increasing recognition in a number of areas of the environmental impacts, both realized and potential, of human activities not only on local and regional scales but also globally. This is particularly true of changes to the composition and chemistry of the atmosphere caused by such anthropogenic activities. One example, for which there is irrefutable evidence, is stratospheric ozone depletion by chlorofluorocarbons, discussed in detail in Chapters 12 and 13. 

In the early 1970s, Mario Molina (b. 1943) of the Massachusetts Institute of Technology, F. Sherwood Rowland (b. 1927) of the University of California, Irvine, and Paul J. Crutzen (b. 1933) of the Max Planck Institute in Germany, all shown in Figure 17.16, recognized the potential threat to stratospheric ozone posed by chlorofluorocarbons (CFCs). Because CFCs are inert gases, they were once commonly used in air conditioners and aerosol propellants. Two of the most frequently used CFCs are shown in Figure 17.17. 

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