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Outline the different techniques and methods of data collection used to investigate the chemistry of the stratosphere

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Introduction

Salters Chemistry Open-book Examination: March, 1997: Ozone and CFCs Ozone is present in the atmosphere in only small amounts, dispersed among other atmospheric gases. Over time, the amount of ozone in the atmosphere has decreased and can be linked to CFCs. Section 1: Outline the different techniques and methods of data collection used to investigate the chemistry of the stratosphere Monitoring involves finding out what chemical species are present in the stratosphere and at what concentrations and includes analysing the air by a form of spectroscopic technique. Measurements can be taken from helium balloons, from satellites and from high altitude planes (Gwen & Mike Pilling 'Do CFCs destroy the ozone layer?' from Chemistry Review, March 1993). Measurements can also be taken from a ground station such as during the British Antarctic Study. Here spectroscopic measurements were taken looking upward through the whole vertical column of air (Gwen & Mike Pilling 'Do CFCs destroy the ozone layer?' from Chemistry Review, March 1993). Laboratory measurements come from laboratory studies of the individual species known to be present in the stratosphere. In order to obtain this information you need to know which species absorb solar radiation, the wavelength of the radiation absorbed and the strength of the absorption. ...read more.

Middle

from Chemistry Review, March 1993). Scientists flew into the ozone hole and measured the concentrations of ClO radicals and ozone. The concentration of ozone fell dramatically at the point where the concentration of ClO radicals soared. This was undeniable evidence that a catalytic cycle involving Cl radicals is involved in ozone depletion. Section 3: Describe the chemical reactions by which ozone is depleted in the stratosphere and explain why ozone depletion is most severe over Antarctica in the southern spring Some gases such as nitrogen dioxide (NO2) and methane (CH4) can react with Cl and ClO radicals and interrupt the catalytic cycle: Cl + CH4 HCl + CH3 ClO + NO2 ClONO2 (Equations from Gwen & Mike Pilling 'Do CFCs destroy the ozone layer?' from Chemistry Review, March 1993). The chlorine atoms become bound up in the stable reservoir molecules, HCl and ClONO2 and remain chemically inactive until released once more when these molecules eventually break down. The formation of such reservoir molecules helps to reduce the loss of ozone at most latitudes. Ozone depletion is dramatic in Antarctic spring due to special weather conditions whereby the sun disappears for 6 months in winter (Salters Chemical Storylines, Second Edition, p75). ...read more.

Conclusion

However, the acceptability of hydrocarbons depends upon the importance of their flammability hazard, the pollution from emissions (photochemical smog) and the energy consumption of the systems (Dr Dick Powell, 'The rise and fall of CFCs' from Chemistry Review, September 1996). After many years of investigation and testing, two refrigerants have emerged as the current industry choice for replacement of CFC-12. They are HFC-134a and MP-39, which is a blend of HCFC-22, HFC-152a and HCFC-124 (http://www.edis.ifas.ufl.edu/EH313). Although less harmful than CFC-12, the HCFCs in MP-39 do have a measurable effect on. HFCs, which contain no chlorine, are more promising. Unfortunately, the ability of HFCs to absorb infrared radiation as a greenhouse gas makes their future acceptability uncertain. HFC-134a, HFC-152a, and HCFC-22 have a Global Warming Potential (GWP) of less than one, as compared with a GWP of 3.0 for CFC-12 (http://www.edis.ifas.ufl.edu/EH313). While HFC-134a appears to be the most environmentally friendly alternative for newly manufactured equipment, MP-39 is more attractive as a replacement for CFC-12 in existing systems. A direct switch to HFC-134a in a system designed for CFC-12 will result in about a 10 percent decrease in refrigeration capacity. This will cause an increase in energy consumption due to the longer run time that will be needed to satisfy the cooling load. ...read more.

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