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Difficulty: EasyGreenhouse Effect, Global Warming, and Ozone Layer Depletion

In atmospheric chemistry, certain active species initiate catalytic cycles that destroy stratospheric ozone. Which of the following species acts as a direct catalyst in the destruction of stratospheric ozone?

  1. Chlorine free radicals (Cl∙\text{Cl}^\bullet)Answer
  2. B
    Carbon(IV) oxide (CO2\text{CO}_2)
  3. C
    Methane (CH4\text{CH}_4)
  4. D
    Water vapour (H2O\text{H}_2\text{O})

Answer

Chlorine free radicals (Cl∙\text{Cl}^\bullet)
Chlorine free radicals participate directly in a catalytic cycle in the stratosphere, converting ozone molecules into oxygen molecules without being permanently consumed in the overall process.

Step-by-Step Solution

1
Identify the cause of catalytic ozone layer depletion in the stratosphere.
Ultraviolet light breaks down chlorofluorocarbon (CFC) molecules, releasing reactive chlorine free radicals (Cl∙\text{Cl}^\bullet).
Photolysis produces reactive atomic chlorine species in the upper atmospheric layers.
2
Examine the catalytic reaction step.
Chlorine radicals react with ozone: Cl∙+O3→ClO∙+O2\text{Cl}^\bullet + \text{O}_3 \rightarrow \text{ClO}^\bullet + \text{O}_2, depleting the ozone layer.
The chlorine radical is regenerated during subsequent reactions, allowing a single radical to break down thousands of ozone molecules.

Key Concept

Catalytic Role of Chlorine Free Radicals in Stratospheric Ozone Depletion
Estimated Time:45s
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Topics

Greenhouse Effect, Global Warming, and Ozone Layer Depletion

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