Question

How is the ozone layer depleted?

Answer 1

• Main cause: long‑lived human chemicals (CFCs, halons) reach the stratosphere and release chlorine and bromine atoms that destroy ozone.
• How it works (mechanism): a free Cl (or Br) atom reacts with O₃ to make ClO and O₂, then ClO reacts with an O atom to regenerate Cl and form more O₂. The net result is O₃ + O → 2 O2, so one halogen atom can destroy many ozone molecules.
• Polar amplification: In very cold polar winters, polar stratospheric clouds convert inert reservoir compounds (like HCl and ClONO₂) into reactive forms (Cl₂) that, when sunlight returns in spring, produce a burst of reactive Cl. This causes the large seasonal Antarctic ozone “hole.”
• Other contributors: Nitrogen oxides, volcanic sulfur emissions, and solar events can also change stratospheric chemistry and speed ozone loss.
• Why CFCs are especially damaging: They are stable in the lower atmosphere, so they persist and reach the stratosphere, but UV there releases halogen atoms that then catalytically destroy ozone over long timescales.