Chemistry of Ozone Depletion by CFCs

Posted on February 27, 2010

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CFCs destroy the ozone in the stratosphere (15 – 20 km above the earth’s surface)
(Ozone concentrations are measure in Dobsen units, 1 Dobsen unit represents 1 molecule of O3 for every 1 billion air molecules)
Ozone loss is greatest over Antarctica where the ozone depletion has been recorded and is commonly referred to as the “ozone hole”.
Ozone (O3), an allotrope of oxygen, is poisonous to humans if breathed in, but is important to life in that it filters out or absorbs short wavelength ultraviolet radiation (u.v) in the 280 – 320nm range which can cause serious sunburn, skin cancer and eye disorders.
The inertness and lack of water solubilty of CFCs mean they are not destroyed nor are they dissolved in rain water so they stay in the atmosphere for a very long time and diffuse up to the stratosphere
In the stratosphere, CFCs come into contact with short wavelength ultraviolet radiation which is able to split off chlorine atoms from the CFC molecules

CCl2F(g) u.v radiation—————> CCl2F(g) + Cl(g)

These chlorine atoms destroy the ozone layer

Cl(g) + O3(g) ————-> ClO(g) + O2(g)

There are significant numbers of oxygen atoms in the stratosphere (since ozone undergoes a natural photochemical decomposition producing oxygen atoms and molecules) which leads to the regeneration of chlorine atoms in the stratosphere.So, 1 CFC molecule can destroy many ozone molecules.

ClO(g) + O(g) ————-> O2(g) + Cl(g)

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