Thermosphere
The thermosphere starts just above the mesosphere and extends to about 600 km high. Temperatures here go up to a staggering 1700 degrees. Chemical reactions occur faster in this part of this atmosphere.
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Identify the main pollutants found in the lower atmosphere and their sources
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Describe how ozone as a molecule is able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant
The ozone is made up of decomposed oxygen molecule reacted with another oxygen molecule.
- The above reactions are exothermic hence explaining why the stratosphere has a high temperature.
The ozone is both a pollutant whilst it also provides protection. This is because ozone molecules have the ability to oxidise many substances. At a lower atmosphere the ozone molecules disrupts biochemical reacting and causes harm to humans by causing irritation and respiratory problems. The picture below shows a leaf discoloured by ozone molecules.
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State the common name , correct iupac name and the correct formula of two cfcs
Common name : Freon
Iupac name : dichlorodifluoromethane
Common name : HCFC-124
Iupac name: chlorotetrafluoroethane
- Identify the source of chlorofluorocarbons and halons in the atmosphere and discuss why they are used.
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.
- 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. The chlorine then reacts with the ozone molecules forming CLO and oxygen. The CLO reacts with oxygen atoms producing oxygen and a chlorine radical which when bonds to another chlorine radical forms chlorine ready to strike again at the ozone.
- Discuss the problems associated with the use of CFCs. Outline the steps taken to address the problems.
As the ozone depletes more UV radiation would reach the surface of the earth causing many problems such as higher water levels and increased rate of cancer. After over 50 years of use, the dangers of the CFC’s were recognised internationally and hence in 1987 the Montreal protocol was signed by nations to alleviate the use of CFCs. The protocol has been extremely affective and all developed countries have ceased used of CFCs, although 3rd world countries still use them. New alternative chemicals have been introduced such as the hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) . Also to help stop the use of CFCs in poor countries assistance is offered.
- Identify the alternative chemical used to replace CFC’s
HCFC’s (hydrochloroflourocarbons) were introduced because They contain less chlorine atoms than in CFC’s providing less damage. HFC ( hydrofluorocarbons) have no chlorine atoms and is not expected to produce unwanted chlorine radicals.
- Describe the changes that occur in atmospheric ozone concentrations.
The changes that occur in atmospheric ozone concentration is dependent on the ozone concentration in that particular place. For example in the Antarctic the ozone concentration is quite low hence this contributes to the fact of rising sea levels thus the melting of the ice.
In 2004 due to the decrease of release of halons and CFCs in to the atmosphere a huge decrease in the rate of ozone depletion has been observed.
- Asses the effectiveness of steps in alleviating the problems associated with the use of CFC’s
First you must understand the only way to stop the ozone depletion is too stop releasing CFC’s into the air. 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.
- 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.
- 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
