Ozone layer, destruction

Ozone layer destruction. The upper atmosphere contains a layer rich in ozone. Whilst ozone in the lower levels of the atmosphere is harmful, ozone in the upper levels... 

Ozone (O3) exists in the atmosphere, 20-40 km above sea level. Ozone absorbs UV radiation which would otherwise harm living things. The effects of ozone loss could include increased human cataracts and skin cancer, reduction of plankton in ocean waters and destruction of plants, including crops. Ozone layer destruction in the Antarctic was reported in 1985 a major cause of this was believed to be the release of chlorofluorocarbon compounds, such as CCI2F2 (CFCs). These compounds are chemically unreactive, non-toxic and odourless, properties which at one time caused them to be used as solvents, aerosol propellants, refrigerant fluids and blowing agents for expanded plastic foams. They are so stable, however, that they persist in the atmosphere for years and eventually enter its upper layers, where they are broken down by the powerful UV radiation emitted by the sun. Their decomposition products can then destroy ozone ... 

Problem-induced TA studies are directed toward acute or foreseeable problems in society, for example, the CO2 enrichment of the atmosphere or ozone layer destruction in the stratosphere by fluorine-chlorine hydrocarbons and the resulting consequences. Here the research leads to consideration of so-called macroalternatives, which lead away from the original problem-solution. 

The most prominent instance of ozone layer destruction is the so-called Antarctic ozone hole that was first firmly established in 1985 by the British Antarctic Survey and observed with great alarm in subsequent years. This phenomenon is manifested by the appearance during the Antarctic s late winter and early spring months of September and October of severely depleted stratospheric ozone (up to 50%) over the polar region. The reasons why this occurs are related to the normal effect of NO2 in limiting Cl-atom-catalyzed destruction of ozone by combining with CIO ... 

Chlorofluorocarbons CFCs and hydrochlorofluorocarbons HCFCs are all anthropogenic species and are the causative agents of ozone layer destruction as well as greenhouse gasses. CFCs are the molecules in which aU the hydrogen atoms of hydrocarbons are substituted by chlorine and fluorine atoms. They do not have absorption bands in the tropospheric actinic flux region and also do not react with OH radicals. Therefore, they do not have any dissipation process in the troposphere, and can be photolyzed only after they reached to the stratosphere. On the other hand, HCFCs is molecules in which at least one of chlorine or fluorine atom of CFCs is substituted by hydrogen atom. Since HCFCs react with OH radicals, they are removed in the troposphere, but a portion of them reach the stratosphere and photolyzed, similar to CFCs. 

Among halocarbons (halogenated hydrocarbons), bromochlorofluorocarbons in which at least one chlorine or fluorine atom of chlorofluorocarbons is substituted by bromine is called halons. Halons, as with CFCs, do not have any dissipating process in the troposphere, and reach to the stratosphere and are photolyzed, which affects the ozone layer destruction. Among halons, Cp2ClBr (halon—1211) and CFsBr (halon-1301) have the highest atmospheric concentratiOTis, and these two compounds are taken up here. 

Atkinson et al. 2007 Sander et al. 2011). Numerous measurements of the rate constants of reaction (5.108) have been made due to its importance related to ozone layer destruction by CFCs. The NASA/JPL panel evaluation No. 17 (Sander et al. 2011) recommends the Arrhenius formula,... 

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."... 

Write the Lewis structure of each of the following reactive species, all of which are found to contribute to the destruction of the ozone layer, and indicate which are radicals (a) chlorine monoxide, CIO (b) dichloroperoxide, Cl—O—O—Cl ... 

Susan Solomon and James Anderson showed that CFCs produce chlorine atoms and chlorine oxide under the conditions of the ozone layer and identified the CFCs emanating from everyday objects, such as cans of hair spray, refrigerators, and air conditioners, as the primary culprits in the destruction of stratospheric ozone. The CFC molecules are not very polar, and so they do not dissolve in rain or the oceans. Instead, they rise to the stratosphere, where they are exposed to ultraviolet radiation from the Sun. They readily dissociate in the presence of this radiation and form chlorine atoms, which destroy ozone by various mechanisms, one of which is... 

The contribution to the destruction of the ozone layer caused by high flying aircraft has been attributed to the following mechanism ... 

Events that take place on a grand scale often can be traced to the molecular level. An excellent example is the depletion of the ozone layer in the Earth s stratosphere. The so-called ozone hole was first observed above the Antarctic in the 1980s and is now being observed above both the Arctic and Antarctic poles. The destruction of ozone in the stratosphere is caused primarily by reactions between chlorine atoms and ozone molecules, as depicted in our molecular inset view. 

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 centuries, the production and destruction of ozone in Earth s ozone layer was constant. Explain why in recent decades the ozone has been depleted faster than it was replaced. 

Life on Earth requires the energy from the Sun as a primary energy source but it must be protected from all of the radiation at shorter wavelengths. Radiation shorter than 323 nm can break the C-C bond and this would lead to mutations or complete photolytic destruction of carbon-based life forms. The protection from the short-wavelength radiation is achieved on Earth in two ways the ozone layer and the photic zone. 

Located several kilometres above the Earth s surface is the stratosphere. Here the ozone layer acts as a filter, protecting life on Earth from harmful low-wavelength ultraviolet radiation known as UV-C, which damages biological macromolecules such as proteins and DNA. In order to understand the effects of anthropogenic input into the stratosphere, the production and destruction of the ozone layer has been studied by a variety of photochemical models and experimental methods. 

---