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Ozone Destruction

NASA Earth Observatory (Illustration courtesy Barbara Summey, SSAI)

 

The stratospheric ozone layer shields life on Earth from the Sun’s harmful ultraviolet radiation. Chemicals that destroy ozone are formed by industrial and natural processes. With the exception of volcanic injection and aircraft exhaust, these chemicals are carried up into the stratosphere by strong upward-moving air currents in the tropics. Methane (CH4), chlorofluorocarbons (CFCs), nitrous oxide (N2O) and water are injected into the stratosphere through towering tropical cumulus clouds. These compounds are broken down by the ultraviolet radiation in the stratosphere. Byproducts of the breakdown of these chemicals form “radicals”—such as nitrogen dioxide (NO2) and chlorine monoxide (ClO)—that play an active role in ozone destruction. Aerosols and clouds can accelerate ozone loss through reactions on cloud surfaces. Thus, volcanic clouds and polar stratospheric clouds can indirectly contribute to ozone loss.  

The animation illustrates how one chlorine atom in the stratosphere can destroy up to 100,000 ozone molecules.

Credit University Of Alaska

Ozone is destroyed by reactions with chlorine, bromine, nitrogen, hydrogen, and oxygen gases. Reactions with these gases typically occurs through catalytic processes. A catalytic reaction cycle is a set of chemical reactions which result in the destruction of many ozone molecules while the molecule that started the reaction is reformed to continue the process. Because of catalytic reactions, an individual chlorine atom can on average destroy nearly a thousand ozone molecules before it is converted into a form harmless to ozone.

Environmental Protection Agency  graphic

Chlorofluorocarbon (CFC): a compound consisting of chlorine(CI), fluorine, and carbon

How ozone is destroyed by CFCs

 

When ultraviolet light waves (UV) strike CFC* (CFCl3) molecules in the upper atmosphere, a carbon-chlorine bond breaks, producing a chlorine (Cl) atom. The chlorine atom then reacts with an ozone (O3) molecule breaking it apart and so destroying the ozone. This forms an ordinary oxygen molecule(O2) and a chlorine monoxide (ClO) molecule. Then a free oxygen** atom breaks up the chlorine monoxide. The chlorine is free to repeat the process of destroying more ozone molecules. A single CFC molecule can destroy 100,000 ozone molecules.

* CFC - chlorofluorocarbon: it contains chlorine, fluorine and carbon atoms.
** UV radiation breaks oxygen molecules (O2) into single oxygen atoms.

 

Chemical equation

CFCl3 + UV Light ==> CFCl2 + Cl
Cl + O3 ==> ClO + O2

ClO + O ==> Cl + O2

The free chlorine atom is then free to attack another ozone molecule

Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2

and again ...

Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2

and again... for thousands of times.

Source: http://www.bom.gov.au/lam/Students_Teachers/ozanim/ozoanim.shtml

 

 

Ozone Depletion in the Antarctic Springtime

1) HCl + ClONO2 → HNO3 + Cl2

2) Cl2 + sunlight → Cl + Cl

3) 2Cl + O32ClO + 2O2

4) 2ClO + 2O → 2Cl + 2O2
______________________

NET = 203 to 302

credit:NOAA

The very thing that makes Ozone good for filtering UV radiation makes it easily destroyed: it is very unstable.

Antarctic Ozone Hole

As winter arrives, a vortex of winds develops around the pole and isolates the polar stratosphere. When temperatures drop below -78°C (-109°F), thin clouds form of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Ozone depletion begins, and the ozone “hole” appears. 

 

Natural events such as Volcanic Eruptions can strongly influence the amount of Ozone in the atmosphere.

However, man-made chemicals such as CFCs or chlorofluorocarbons are now known to have a very dramatic influence on Ozone levels too. CFCs a were once widely used in aerosol propellants, refrigerants, foams, and industrial processes.

 

 

 

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Data compiled from The British Antarctic Study, NASA, Environment Canada, UNEP,EPA and other sources as stated and credited 

Updated Daily-Researched By Charles Welch- 

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