Which anthropogenic compound is a major cause of stratospheric ozone depletion?

• A. Carbon dioxide
• B. Chlorofluorocarbons
• C. Methane
• D. Nitrogen oxides

Answer: (B)

Stratospheric ozone depletion is driven by halogen radicals released from human-made chlorinated compounds. Chlorofluorocarbons are very stable in the lower atmosphere, so they travel up to the stratosphere intact. There, sunlight breaks them apart and releases chlorine atoms. Those chlorine atoms act as catalysts in reactions that repeatedly destroy ozone: Cl + O3 → ClO + O2, then ClO + O → Cl + O2, and the chlorine atom is freed to destroy many more ozone molecules. This catalytic cycle means a single chlorine atom can destroy thousands of ozone molecules, making CFCs the major anthropogenic cause of ozone loss. Other gases like carbon dioxide and methane are primarily greenhouse gases and don’t drive stratospheric ozone depletion in the same way, while nitrogen oxides can influence ozone chemistry but are not the main culprits on a global scale.