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Chemical monitoring and management - composition of the atmosphere and the problems of pollution.

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Introduction

Chemical monitoring and management Part A 1. describe the composition and layered structure of the atmosphere. First of all the atmosphere is a blanket of air which surrounds the earth. The atmosphere has many functions to maintain life on earth. This includes protection of UV radiation, vacuum of space and is part of the process of photosynthesis. There are 4 different layers in the atmosphere of the earth. All of these layers have been recognised due to the chemical composition, the density and thermal composition. Troposphere The troposphere is the first layer of the atmosphere starting from the surface of the earth. It extends about 15 km upwards from the surface of the earth. In this layer the temperature drops from 17 to -52 degrees. 90% of earth's gases are present in the troposphere. The upper region of the troposphere is very stable. This region is called the tropopause. This region helps in reducing the mixture of gases. Stratosphere In this layer the ozone of the earth is present. Hence the temperature of the stratosphere increases to about -3 degrees due to the hot UV radiation present in this region of the atmosphere. Thus this region compared to the troposphere is very dry. ...read more.

Middle

In the 1930's Ammonia was replaced with CFCS because at the time the properties of the CFC's were found to be 'safer' than ammonia. The inertness and low boiling point of the CFC'S led to them being used as solvents, propellants and blowing agents in foam. CFC's were extensively used as refrigerants.Halons (brominated CFC) are haloakanes which was developed to extinguish electrical fires. CFCs once used would gradually make its way up into the atmosphere. Because of their inertness would not disintegrate in the troposphere and would end up in the stratosphere where the C-CL bonds and C-Br bonds break due to the UV radiation hence depleting the ozone layer. 6. Present equations to show the reaction involving CFCs and ozone to demonstrate the removal of ozone from the atmosphere. CFC's undergo a process called photo dissociation which is a type of reaction in which Energy of light is used to break the bonds. Thereupon they release chlorine, bromine atom radicals. It is these radicals which destroy the o3 molecules which make up the ozone. 1) CClF3(g) + UV radiation ? CF3(g) + Cl�(g) 2) Cl�(g) + O3(g) ? ClO(g) + O2(g) 3) ClO(g) + O(g) ? O2(g) + Cl�(g) The above reactions show how the CFC gets broken up into chlorine and CF3. ...read more.

Conclusion

Many international agreements such as the Vienna convention and the Montreal protocol and further agreements in London and Copenhagen ensured that the use of CFC'S will be stopped over time. To the poor countries which still use CFCs financial aid is given in meeting the criteria of the agreements covered in the meetings. Recent research show the successfulness of the meetings. 11. Evaluate the effectiveness of the use of alternative chemical as a replacement for CFCs. Alternative chemicals such as HCFC and HFC have been introduced. HCFC has less chlorine atoms but still disintegrates the ozone layer. On the other hand HFCs have no chlorine bonded to them hence are environmentally and ozone friendly. The only disadvantage of this chemical is that it is expensive and is less efficient than the CFC it replaces. 12. Explain how information on changes in atmospheric ozone concentrations was obtained. Total Ozone Mapping Spectrophotometers or (TOMS) are instruments used onboard satellites to scan and measure ozone concentrations in the stratosphere. Since the ozone layer is present at the stratosphere, the ozone concentrations are usually monitored from balloons, satellite and ground based instruments In the late 80's the ozone spectrometer onboard the nimbus 7 satellite recorded thinning of the ozone layer at a significant rate over Antarctica. This led to the acceptance of the theory of CFCs and the chlorine radicals they produce in disintegrating the ozone layer. Hoon Kim yr 12 ...read more.

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