How are chlorofluorocarbon responsible for the depletion of ozone layer ?

Chlorofluorocarbons (CFCs) are responsible for ozone layer depletion through the following mechanisms:

1. Stability and Longevity: CFCs are highly stable and inert in the troposphere, allowing them to reach the stratosphere where ozone is concentrated.

2. UV Radiation Breakdown: In the stratosphere, strong ultraviolet (UV) radiation breaks CFCs into free chlorine radicals (Cl·) and fluorine radicals (F·). The key reaction is: $$\mathrm{CFCl}{}_3\to \mathrm{CFCl}{}_2+\mathrm{Cl}\cdot$$

3. Catalytic Destruction of Ozone: Chlorine radicals act as catalysts in the destruction of ozone ($O_3$) through a series of reactions:

   • Initiation: $$\mathrm{Cl}\cdot +\mathrm{O}{}_3\to \mathrm{ClO}\cdot +\mathrm{O}{}_2$$
   • Propagation: $$\mathrm{ClO}\cdot +\mathrm{O}\to \mathrm{Cl}\cdot +\mathrm{O}{}_2$$ The chlorine radical (Cl·) is regenerated, allowing it to destroy thousands of ozone molecules in a catalytic cycle.

4. Net Effect: Each chlorine atom can destroy up to 100,000 ozone molecules before being removed from the stratosphere, leading to significant ozone depletion.

The presence of CFCs in the stratosphere disrupts the natural balance of ozone formation and destruction, resulting in the thinning of the ozone layer.