Ozone Depletion by Chlorofluorocarbons

It has also been speculated that the concomitantly generated perfluoroalkyl radicals play a minor role in ozone depletion but, in contrast with chlorine, the trifluor-omethyl radical, for example, is cleared from the atmosphere relatively quickly via its irreversible conversion to carbonyl difluoride (GF2O) [28]. Whereas bromine 

When Molina and Rowland made their prediction in 1974, world production of CFCI3 and CF2CI2 was approximately 0.3 and 0.5 Mton respectively fluorocarbon production in the US was growing by 8.7% per year around 1970 [27]. Six years later, and every year since then, the predicted ozone hole was detected over Antarctica, when the chlorine concentration in the same atmospheric layer was approximately 2000 pmol mol [29]. After this dear evidence of the deleterious effects of CFC, in 1987 this class of substance and most bromofluorocarbons were banned from further industrial use in the Montreal Protocol (ratified by the first 29 states in 1989). Because of the decade-long lifetime of stratospheric CFC, their phasing-out can be expected to show an effect no earlier than approximately 2040. 

Because CFC had many essential functions in all aspects of our daily life (for example refrigerants, foaming agents, or propellants for aerosol cans), subsequent to the Montreal Protocol an intensive search for potential replacements was initiated. CFC replacements so far include hydrofluorocarbons (HFC for example CF3CFH2, marketed as HFC-134a), hydrochlorofluorocarbons (HCFC), and partially fluori-nated ethers (for example CH3OCF3). These substances are much less stable to attack by radicals in the lower atmosphere and thus cannot reach the stratosphere where they would deplete the ozone layer [30]. 

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Global Warming and increased Climatic Variability due to Greenhouse Gas (GHG) Accumulation in the Atmosphere and Increased Radiation due to Ozone Depletion by Chlorofluorocarbons (CFC). 

F. S. Rowland. Stratospheric Ozone Depletion by Chlorofluorocarbons. 1995 Nobel Lecture. Angewandte Chemie. International English edition. 35 (Sept. 6, 1996) 1786-1798. 

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. 

R. S. Stolarski, The Antarctic Ozone Hole, Scientific American, January 1988. The 1995 Nobel Prize in Chemistry was shared by Paul Crutzen, Mario Molina, and F. Sherwood Rowland for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone. Their Nobel lectures can be found in P. J. Crutzen, My Life with 03, NO, and Other YZO Compounds, Angew. Chem. lnt. Ed. Engl. 1996,35, 1759 M. J. Molina, Polar Ozone Depletion, ibid., 1779 F. S. Rowland, Stratospheric Ozone Depletion by Chlorofluorocarbons, ibid., 1787. 

Progress has been made in some areas since 1970. Emissions of pollutants from point sources into air and water have decreased. Toxic releases are decreasing. Some Superfund sites have been cleaned up. Businesses would no longer think of dumping a barrel of waste solvent on the ground at the landfill site so that the barrel could be used again for the same purpose. Control of pollutants from nonpoint sources is still a problem. There is now more international cooperation and discussion of global problems, such as ozone depletion by chlorofluorocarbons and the effect of... 

This chapter has outlined the history and conceptual understanding of the processes responsible for ozone depletion by chlorofluorocarbons in the stratosphere. In brief, the long lifetimes of chlorofluorocarbons are reflected in their observed worldwide accumulation in the atmosphere. Their role in stratospheric ozone depletion depends critically on... 

Ozone is one of the strongest oxidants known. We briefly touched on the ozone layer and the chemistry of ozone depletion by chlorofluorocarbons. 

Free-radical chain reactions also occur during the chlorination of methane (Chapter 10) and of the methyl group of methylbenzene. Ozone depletion by chlorofluorocarbons (CFCs), acid rain formation and formation of photochemical smog (Chapter 25 on the accompanying website) also involve free-radical reactions. (Free-radical reactions are also operating in unpolluted atmospheres and play an important role in all chemical reactions that occur in the gas phase.) The combustion of hydrocarbons, such as petrol, also proceeds via a free-radical mechanism, which has important consequences for the smooth running and performance of combustion engines. Chain reactions may also have ions as intermediates, as opposed to free radicals. 

Another important mutagen is ultraviolet light. Recent concern about the depletion of the atmospheric ozone layer by chlorofluorocarbon compounds (CFCs) is due to the role of the ozone in absorbing UV radiation before it can cause mutations in the organisms at the earth s surface. All the DNA bases efficiently absorb UV and become chemically reactive as a result. The formation of pyrimidine dimers from adjacent thymidine residues in DNA interferes with replication and transcription of DNA. See Figure 8-14. 

The major chlorine oxides, CIO, CI2O, CIO2, and CI2O7, are rather unpleasant, explosive substances. Chlorine oxide is of central importance in accounting for the depletion of the ozone layer by chlorofluorocarbons and is discussed in Section 18.6. Dichlorine oxide is a powerful chlorinating agent and an important commercial bleach. It is used industrially to produce household bleaching powder, Ca(OCl)2, as shown in Equation (18.26) ... 

As we also saw in Section 6.10, the layer of ozone in the upper atmosphere plays an important role in the absorption of harmful ultraviolet radiation from the sun. It absorbs the UV radiation and breaks apart to O2 and O. This oxygen atom will often react with another O2 molecule to re-form as ozone. During this cycle, each ozone molecule absorbs many ultraviolet photons. Recall also from Section 6.10 that the ozone layer has been depleted by chlorofluorocarbons (CFCs). However, legislation has banned CFCs in the hope that their reduction will help the ozone layer to recover. 

Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

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."... 

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... 

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... 

Amorphous fluoropolymers have many applications in the areas of advanced materials where they are used in applications requiring thermal and chemical resistance. Their manufacture is hindered by their low solubility in many solvents. Many fluoropolymerizations cannot be carried out in hydrocarbon solvents because the radical abstraction of hydrogen atoms leads to detrimental side reactions. Chlorofluorocarbons (CFCs) were thus commonly used, but their use is now strictly controlled due to their ozone depleting and greenhouse gas properties. Supercritical carbon dioxide is a very attractive alternative to CFCs and it has been shown that amorphous fluoropolymers can be synthesized by... 

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