Chemistry of the stratosphere
This information business lead to the conclusion that Cl radicals any very long lifetime and one radical could destroy 100 1000 molecules of ozone. Considerable global monitoring of CFCs was carried out in addition to this amount was in comparison with the amounts introduced in troposphere and that was concluded that most of the molecules released were still there. The chemicals reactions by which ozone is depleted in the stratosphere and why ozone depletion is most severe above Antarctica inside the southern springtime. Ozone depletion occurs by the release of CFCs and some other ozone-depleting substances. A single chlorine atom can break about 1million ozone molecules.
When CFCs reach the stratosphere, the sturdy ultraviolet radiation from the particular sun breaks them aside, releasing chlorine which react with ozone. Cl & O3 ClO + O2 ClO formed is one more radical which reacts along with oxygen atoms. ClO & O2 Cl + O2 This could start the particular chemical cycles of ozone destruction depleting the ozone layer. Cl atoms are regenerated and can go on to react with more O3 Following is another way that the ozone could be removed. O + O3 O2 + O2 Hydroxyl radicals can also play a part inside the depletion of ozone. HO + O3 HO2 + O2 The HO2 could then react with oxygen atoms. HO2 + O HO + O2
The ozone depletion is most severe over Antarctica in the southern spring which results from the weather conditions in winter because the sun disappears for a period of six months. Air cools down making the temperature fall and clouds form in the stratosphere. These clouds contain particles of nitric acid triydrate (HNO33H2O) below 195K which are frozen around the sulphuric acid nuclei. A reduction in temperature leads to the condensation of water vapour as ice on the surface of these particles. The solid particles offer a surface for the chemical reactions to take place. Chlorine reservoirs collect on these surfaces and react.
HCl + ClONO2 cloud Cl2 + HNO3 surface These chlorine atoms are released in to the stratosphere. Te return of sunlight after six months splits the chlorine molecules into chlorine atoms which leads to dramatic fall in the ozone concentration. Why the CFCs have been used so widely and the advantages and disadvantages of their replacements Chlorofluorocarbons are found to combine lox toxicity, high chemical stability and non-flammability with good performance. CFCs and the HCFCs were use as refrigerants because they have appropriate boiling point which is low enough to evaporate efficiently but high enough to liquefy by compression.
They also have a freezing point low enough to prevent the liquid from solidifying. CFCs were used for several applications, which include air conditioners, water chillers, aerosols, domestic fridges and freezers, dry cleaning and biomedical freezers. After discovering regarding the ozone depletion related to the use of CFCs, various other substances may be found which would be eco-friendly. HFCs seemed like the solution. The hydro fluorocarbons (HFCs) compounds contain only carbon, hydrogen and fluorine. They are chosen because they contain fluorine because their only halogen.
Free fluorine atoms can only be liberated from a fluorine-containing substance by putting in a considerable amount of energy. This required energy input is far more than comes in the solar radiation I the stratosphere. If the fluorine atom was to be produced, it would be highly reactive and would abstract a hydrogen atom from a molecule like water to form an inert hydrogen fluoride. No free fluorine atoms in the stratosphere would certainly lead to no ozone destruction. Also, HFCs are usually destroyed in the reduced atmosphere by hydroxyl foncier so only a tiny proportion can reach the stratosphere.
Typically the disadvantage of using HFCs is that the products was designed to optimise the performance of CFCs and HCFCs and typically the usage of HFCs would entail the redesigning of just about all the equipment. In upcoming, cooling technologies not involving HFCs maybe introduced, specifically where they have technical advantages and where typically the potential hazards can be very easily controlled.
1) Exactly how do we know of which CFCs destroy the ozone layer? By Mike Pilling. Chemistry Review, March 1993. Philip Allan Publishers Limited. 2) The rise in addition to fall of CFCs by Dr Richard Dick Powel. Chemistry Review, September 1996. Philip Allan Publishers Ltd: http://www.epa.gov