Chlorofluorocarbons ozone destruction

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... 

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... 

The production of chlorofluorocarbons, or CFCs, has been banned by international treaty because of their deleterious effect on the ozone layer. The ozone layer absorbs much of the Sun s dangerous UV radiation before it reaches the Earth s surface. CFCs are extremely stable in the lower atmosphere (one reason why they are so useful), but when they reach the stratosphere they decompose, producing potent catalysts of ozone destruction. Ozone destruction is most evident above Antarctica during the spring, when this region is exposed to the Sun for the first time in months. Dichlorodifluoromethane (CF2CI2) is a typical CFC. 

Thus these additional reactions in the stratosphere decrease significantly the rate of ozone destrnction processes, especially nnder contamination of the atmosphere by chlorofluorocarbons and nitrous oxides as the catalysts of ozone destruction reactions. 

Chlorofluorocarbons have unique chemical and thermodynamic properties that make them very attractive for a wide variety of applications, ranging from refrigeration and air conditioning to foam blowing and medical sterilants. Unfortunately, as mounting evidence shows, their inertness allows CFCs to be transported to the stratosphere, where their photolysis releases chlorine atoms that participate in catalytic ozone destruction. Consequently, the manufacture and use of these compounds is being phased out. 

Ozone destruction begins with chlorofluorocarbons such as Freon-12 (CCI2F2) from refrigerants. These long-lived compounds diffuse to the stratosphere, where they catalyze ozone decomposition ... 

A major concern with chlorofluorocarbons is destruction of the ozone layer (mentioned in"Chemical Connections Freons Tn this chapter).The ozone-consuming reactions are thought to occur through a radical chain mechanism. The production of one radical species derived from a CFC can destroy a large number of ozone molecules before any termination steps occur. 

In view of the environmental problems such as the greenhouse effect and stratospheric ozone destruction, mainly caused by chlorofluorocarbons (CFC), the database was extended to thermophysical properties of environmentally acceptable refrigerants (Stephan Krauss 1990). 

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 ... 

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). 

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. 

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. 

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

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