Explain ozone depletion conceptually and how CFCs contribute.

• A. Ozone absorbs UV radiation and exists independently of CFCs.
• B. Ozone destruction is promoted primarily by methane oxidation products, not chlorine.
• C. Ozone concentration remains constant despite UV exposure and pollutants.
• D. CFCs release chlorine radicals that catalytically destroy ozone, reducing ozone concentration.

Answer: (D)

Ozone depletion is driven by catalytic cycles that involve halogen radicals released from stable compounds like CFCs. The ozone layer’s job is to absorb most of the sun’s UV radiation, so when ozone is destroyed, UV can reach the surface more readily. CFCs are very stable in the lower atmosphere and can travel up to the stratosphere, where sunlight breaks them apart to release chlorine atoms. Those chlorine atoms kick off cycles that destroy ozone efficiently: a chlorine atom reacts with ozone to form chlorine monoxide and oxygen, and then the chlorine monoxide reacts with a separate oxygen atom to regenerate the chlorine atom and produce another molecule of O2. The chlorine radical is regenerated each cycle, so one chlorine atom can destroy many ozone molecules, dramatically lowering ozone concentration. That’s why CFCs are linked to ozone depletion. Methane-derived species do play a role, but in the stratosphere the chlorine-catalyzed cycle from CFCs is the dominant mechanism, and ozone levels are not constant or independent of UV exposure.