Ozone layer depletion is primarily caused by certain human-made substances known as ozone-depleting substances (ODS). The most significant of these substances are chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform. Among these, CFCs are the most notorious agents responsible for the depletion of stratospheric ozone.
The process of ozone depletion by CFCs can be summarized as follows:
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Release of CFCs into the atmosphere: CFCs are released from products like aerosol sprays, refrigeration, and foam-blowing agents. Once released, they can take many years to reach the stratosphere.
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Breakdown of CFCs by UV radiation: In the stratosphere, ultraviolet (UV) radiation from the sun breaks down CFCs, releasing chlorine atoms:
\[ \text{CCl}_3\text{F} \xrightarrow{UV} \text{CCl}_2\text{F} + \text{Cl} \]
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Chlorine atoms catalyze ozone destruction: The free chlorine atoms can react with ozone (O₃) molecules to form oxygen (O₂) and chlorine monoxide (ClO):
\[ \text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \]
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Regeneration of chlorine atoms: The chlorine monoxide can react with a free oxygen atom and release the chlorine atom, allowing it to continue the cycle of ozone destruction:
\[ \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \]
This cycle allows a single chlorine atom to destroy thousands of ozone molecules before it is removed from the stratosphere. Therefore, the presence of CFCs and other similar substances has a significant and detrimental impact on the ozone layer.
Summary of the Equations:
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CFC breakdown: \[ \text{CCl}_3\text{F} \xrightarrow{UV} \text{CCl}_2\text{F} + \text{Cl} \]
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Ozone destruction: \[ \text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \]
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Regeneration of chlorine: \[ \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \]
These reactions highlight the mechanism through which CFCs contribute to ozone layer depletion.