Chlorofluorocarbons destruction

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."... 

Despite their instability (or perhaps because of it) the oxides of chlorine have been much studied and some (such as CI2O and particularly CIO2) find extensive industrial use. They have also assumed considerable importance in studies of the upper atmosphere because of the vulnerability of ozone in the stratosphere to destruction by the photolysis products of chlorofluorocarbons (p. 848). The compounds to be discussed are ... 

The following mechanism has been suggested to explain the contribution of chlorofluorocarbons to the destruction of the ozone layer ... 

C15-0130. If chlorofluorocarbons catalyze O3 decomposition, which is exothermic by 392 kJ/mol, they must also catalyze O3 production from O2. Using the energies shown in Figure 15-20. explain why catalysis results in net O3 destruction even though reactions in both directions are accelerated. 

The term CFCs is a general abbreviation for ChloroFluoroCarbons. They have been extensively used since their discovery in the thirties, mainly as refrigerant, foam blowing agent, or solvent because of their unique properties (non toxic, non flammable, cheap). However, after the first warning of Rowland and Molina [1] in 1974 that CFCs could destroy the protective ozone layer, the world has moved rapidly towards a phase-out of CFCs. Because the destruction of stratospheric ozone would lead to an increase of harmful UV-B radiation reaching the earth s surface, the production and use of CFCs is prohibited (since January 1, 1995 in the European Union and since January 1, 1996 worldwide). 

For the next thirty years, Thomas Midgley was revered as a scientist who had made our lives healthier and happier. Only in the closing decades of the twentieth century could other scientists detect the far-reaching damage caused by our reliance on his leaded gasoline and chlorofluorocarbon refrigerants. Yet such was his creativity that many years ago he and his associates also invented some of today s substitutes for their destructive CFCs. 

In order to calculate the steady-state concentration of ozone in the stratosphere, we need to balance the rate of production of odd oxygen with its rate of destruction. Chapman originally thought that the destruction was due to the reaction O + 03 —> 2O2, but we now know that this pathway is a minor sink compared to the catalytic destruction of 03 by the trace species OH, NO, and Cl. The former two of these are natural constituents of the atmosphere, formed primarily in the photodissociation of water or nitric oxide, respectively. The Cl atoms are produced as the result of manmade chlorofluorocarbons, which are photodissociated by sunlight in the stratosphere to produce free chlorine atoms. It was Rowland and Molina who proposed in 1974 that the reactions Cl + 03 —> CIO + O2 followed by CIO + O —> Cl + O2 could act to reduce the concentration of stratospheric ozone.10 The net result of ah of these catalytic reactions is 2O3 — 3O2. 

You probably know that compounds called chlorofluorocarbons (CFCs) are responsible for depleting the ozone layer in Earth s stratosphere. Did you know, however, that CFCs do their destructive work by acting as homogeneous catalysts Use the Internet to find out how CFCs catalyze the decomposition of ozone in the stratosphere. To start your research, go to the web site above and click on Web Links. Communicate your findings as a two-page press release. 

Chemical Family a group of elements that share similar chemical properties and share the same column in the periodic table, for example, halogens, alkali earth Chirality condition that describes the handedness of a molecule or whether a molecule exists in forms that can be superimposed on each other Chlorofluorocarbons also called CFCs, compounds consisting of chorine, fluorine, and carbon that are responsible for stratospheric ozone destruction Coagulation precipitation or separation from a dispersed state Coefficient of Thermal Expansion measure of the rate at which a substance will expand when heated... 

Methane is removed continually from the atmosphere by reaction with OH radicals (Section 8.3). In contrast, chlorofluorocarbons and related volatile compounds are inert under the conditions of the lower atmosphere (troposphere), so atmospheric concentrations of these refrigerants and solvents will tend to increase as long as releases continue. The chief concern over chlorofluorocarbons is that they are a major factor in destruction of the stratospheric ozone layer (Section 8.3). They have been banned under the Montreal Protocol of 1988, but it is important that whatever substitutes (inevitably greenhouse active) are introduced to replace them degrade relatively quickly in the troposphere to minimize any contribution they may be capable of making to greenhouse warming. 

In 1974, F. Sherwood Rowland and Mario Molina, who shared the 1995 Nobel Prize in Chemistry with Crutzen, showed that chlorine from photolyzed chlorofluorocarbons (CFCs) such as CF2C12 and CFCI3, which were used as supposedly inert refrigerants, solvents for cleaning electronic components, plastic foam blowing agents, and aerosol spray propellants, can also catalyze ozone loss. Subsequently, the chlorine monoxide molecule CIO, which is involved in the chlorine-catalyzed ozone destruction cycle, has been shown to be present in the holes in the ozone layer and to correlate inversely with... 

What role do chlorofluorocarbons play in the catalytic destruction of ozone ... 

The answer is a definite yes. Ever since Mendeleyev transformed a simple list of elements into a useful scientific tool, the periodic table has been the doorway through which researchers of all kinds can explore the universe of matter. Old elements are put to new uses, like the zinc nanoparticles in sunscreen. Familiar reactions are found to create serious problems, such as the destruction of the ozone layer by chlorofluorocarbons. Like Mendeleyev himself, scientists are predicting the existence of brand-new elements that have never been seen but are certain to be built someday in the laboratory. 

All of the chlorofluorocarbons and halons discussed above have been implicated in the halogen atom-catalyzed destruction of atmospheric ozone. As a result of U.S. Environmental Protection Agency regulations imposed in accordance with the 1986 Montreal Protocol on Substances that... 

On the global-scale, the destruction of ozone by halocarbons was addressed in the U.S. by banning chlorofluorocarbons in aerosol products. The release of carbon dioxide to the atmosphere from fossil fuel combustion wil1 continue well into or through the twenty-first century. Energy requirements of nations of the temperate zone will require combustion of gas, oil and coal and the atmospheric burden of carbon dioxide will continue to increase with uncertain consequences. 

Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of the ozone layer is due to the breakdown of certain chlorine- or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules. 

Chlorofluorocarbon 12, a freon, was used in refrigeration systems and air conditioners and as an aerosol propellant because of its high stability and low toxicity. Its stability results in environmental problems. It does not decompose until it reaches the upper atmosphere, where ultraviolet light causes the carbon-chlorine bonds to break.The resulting chlorine atoms catalyze the destruction of ozone, resulting in the infamous ozone hole.The use of this and other stable freons has recently been phased out. 

In the current publication we shall discuss the specific features of the reactions of nanoscale MgO and Ti02 with chlorofluorocarbons and the effect of carbon on the performance of the destructive sorbents. 

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