Ozone layer depletion is primarily caused by several man-made chemicals, most notably chlorofluorocarbons (CFCs), halons, carbon tetrachloride (CCl₄), and methyl chloroform (CH₃CCl₃). These substances release chlorine and bromine atoms in the stratosphere, which catalyze the breakdown of ozone (O₃) into oxygen (O₂).
Key Chemical Reactions
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Release of Chlorine from CFCs: Chlorofluorocarbon (CFC) molecules, when exposed to ultraviolet (UV) radiation, can break down and release chlorine atoms.
For example, the breakdown of trichlorofluoromethane (CFC-11 or CCl₃F): \[ \text{CCl}_3\text{F} \xrightarrow{\text{UV}} \text{CCl}_2\text{F} + \text{Cl} \]
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Destruction of Ozone: The free chlorine atom then reacts with an ozone molecule (O₃). This reaction converts ozone into oxygen.
\[ \text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \]
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Regeneration of Chlorine: The chlorine monoxide (ClO) can react with another free oxygen atom, releasing the chlorine atom to destroy more ozone.
\[ \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \]
Overall Reaction Cycle:
Combining these steps, we see how one chlorine atom can destroy many ozone molecules:
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Ozone Destruction: \[ \text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \]
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Chlorine Regeneration: \[ \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \]
In total, one chlorine atom can destroy thousands of ozone molecules before it is removed from the stratosphere via other reactions. The primary impact is a depletion of the ozone layer, which protects the Earth from harmful ultraviolet radiation.
Summary
In summary, substances like CFCs release chlorine, which then participates in a cycle that leads to the degradation of ozone in the stratosphere, resulting in ozone layer depletion.