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

Atmospheric pollutants contribute to environmental degradation through distinct chemical and physical processes. Which of the following statements correctly contrasts the mechanism of carbon(IV) oxide (CO2\text{CO}_2) in global warming with that of chlorofluorocarbons (CFCs\text{CFCs}) in ozone layer depletion?

  1. Carbon(IV) oxide absorbs re-radiated terrestrial infrared radiation in the troposphere, whereas chlorofluorocarbons undergo photolysis in the stratosphere to release free radicals that catalytically destroy ozone.Answer
  2. B
    Carbon(IV) oxide decomposes under solar ultraviolet radiation in the stratosphere to destroy ozone, whereas chlorofluorocarbons absorb infrared radiation exclusively in the thermosphere.
  3. C
    Carbon(IV) oxide acts as a homogeneous catalyst for ozone destruction in the troposphere, whereas chlorofluorocarbons reflect incoming solar radiation back into space.
  4. D
    Carbon(IV) oxide traps high-energy ultraviolet radiation near the Earth's surface, whereas chlorofluorocarbons absorb outgoing terrestrial infrared radiation to cause stratospheric cooling.

Answer

Carbon(IV) oxide absorbs re-radiated terrestrial infrared radiation in the troposphere, whereas chlorofluorocarbons undergo photolysis in the stratosphere to release free radicals that catalytically destroy ozone.
The statement accurately distinguishes the physical warming mechanism in the troposphere (absorption of outgoing long-wave thermal infrared radiation by carbon(IV) oxide) from the photochemical catalytic mechanism in the stratosphere (solar UV photolysis of chlorofluorocarbons yielding free chlorine radicals that decompose ozone).

Step-by-Step Solution

1
Analyze the atmospheric role and mechanism of carbon(IV) oxide (CO₂)
CO₂ is a major greenhouse gas located mainly in the troposphere. It allows short-wave solar radiation to pass through but absorbs longer-wave terrestrial infrared (heat) radiation, preventing its loss into space and driving global warming.
Understanding the physical interaction of greenhouse gases with thermal radiation clarifies how global warming occurs.
2
Analyze the atmospheric role and photolysis mechanism of chlorofluorocarbons (CFCs)
CFCs diffuse unchanged into the stratosphere, where high-energy solar UV radiation photolyzes C-Cl bonds to generate reactive chlorine free radicals (Cl•).
UV radiation provides the activation energy needed for homolytic cleavage of chlorofluorocarbons in the upper atmosphere.
3
Examine the catalytic ozone destruction cycle caused by chlorine radicals
The chlorine radical reacts with stratospheric ozone: Cl• + O₃ → ClO• + O₂ followed by ClO• + O• → Cl• + O₂, regenerating the chlorine radical for further destruction.
A single chlorine radical can destroy thousands of ozone molecules via a catalytic propagation cycle.
4
Synthesize the contrast between the two atmospheric phenomena
Global warming involves tropospheric trapping of thermal infrared radiation by gases like CO₂, whereas ozone depletion involves stratospheric catalytic destruction of O₃ by chlorine radicals produced via photolysis of CFCs.
Distinguishing between tropospheric thermal trapping and stratospheric photochemical radical reactions avoids misattributing pollutant functions.

Key Concept

Greenhouse Effect vs Stratospheric Ozone Depletion Mechanisms
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Topics

Greenhouse Effect, Global Warming, and Ozone Layer Depletion

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