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Techniques + methods used to investigate the chemistry of the stratosphere And links to CFCs

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OPEN BOOK PAPER 1997 TECHNIQUES + METHODS USED TO INVESTIGATE THE CHEMISTRY OF THE STRATOSPHERE AND LINKS TO CFCS It is now an internationally accepted scientific fact that the reactions involving man-made CFCs emitted are responsible for some ozone depletion in the stratosphere. This can be proved in numerous different ways, one early way was to send up helium balloons or planes, With this we are can find out what molecules are present in the stratosphere by the use of infra-red and ultra-violet absorption spectra [1]. All chemicals have different characteristic absorption spectrums. Ozone has a specific absorption range at Ultraviolet radiation of wavelengths below 360nm. By analysing the strength of absorption at these wavelengths, we can work out the concentration of the Ozone present. Measurements are taken in a wide variety of conditions to give us an insight into the normal composition of the stratosphere, but to measure a rate of change we require continuous measurements. Because of the random nature of balloon and plane flights, ground-based stations were setup to take measurements continuously by looking directly upwards into sky, using the sun's rays as the light source. ...read more.


James Loverlock developed a method to detect CFCs in the troposphere and found that they are so stable that they will accumulate in the atmosphere. Then, Sherwood Rowland found that CFCs will absorb the high energy ultra-violet radiation and release Cl in the stratosphere, which can react with 100,000 molecules of ozone. Ten years later, in 1987, Farman discovered the ozone hole by measurement. Scientist also flew over the hole and found that there is a drop in Ozone where ClO concentration is highest. This is shown below in the diagram which also shows the corresponding ClO concentrations. A satellite image showing a hole in the ozone layer over Antarctica (right) & Arctic (left), http://www.jpl.nasa.gov/archive/mpe.html In the South Pole, the sun disappears in winter and a vortex of cold air forms. This cause clouds to be formed in the stratosphere and they are usually frozen sulphuric acid with nitric acid trihydrate (HNO3�3H2O) coated around them. At 190K, water vapour will condense as ice on these particles as well. ...read more.


HFCs don't destroy ozone because fluorine is strongly bound to the carbon and even the energy given by ultraviolet rays is not enough to liberate the fluorine. Some of these replacements have less energy efficiency than the original CFCs. HFCs are also used as a replacement in the short term - they again have similar properties to CFC but they can still cause small amounts of ozone depletion. The cost for manufacturing HFCs are higher then CFCs as was equipment is needed to suit the properties of HFCs (equipment needed to work at slightly higher pressures). In some cases, a replacement is not even needed at all - many aerosols are being replaced by air pumps or electrostatic charged sprays. This reduces the amount of chemical released into the atmosphere. But they are expensive to implement and are inconvenient. ABSTRACT Scientists have linked that the use of CFCs the release of chlorine radicals which destroy the steady state of ozone and oxygen, this was done though such methods as spectroscopy and flash photolysis. CFCs were used in refrigeration, aerosols and cleaning products. HFCs where introduced but there were some difficulties in doing this. ...read more.

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