Which of the following chemical species is responsible for the depletion of the ozone layer in the stratosphere through a catalytic cycle?

Solution

1. Chlorofluorocarbons (CFCs) release chlorine atoms in the stratosphere upon UV irradiation: ${\text{CF}}_2{\text{Cl}}_2\stackrel{h\nu }{\to }\cdot {\text{CF}}_2\text{Cl}+\text{Cl}\cdot$.
2. The chlorine radical reacts with ozone: $\text{Cl}\cdot +{\text{O}}_3\to \text{ClO}\cdot +{\text{O}}_2$.
3. The chlorine monoxide radical then reacts with atomic oxygen: $\text{ClO}\cdot +\text{O}\to \text{Cl}\cdot +{\text{O}}_2$.
4. The chlorine radical is regenerated, continuing the catalytic cycle.
5. Hence the answer is (A).