[short_answer] Explain how ozone is formed naturally in the upper atmosphere. Name the group of chemicals mainly responsible for the depletion of the ozone layer, and state two harmful consequences of ozone layer depletion.
Generated by claude-sonnet-4-6 · 2026-06-26 00:59 · grounding rag
Model Answer
Formation of Ozone:
UV radiation from the Sun splits oxygen molecules (O₂) into free oxygen atoms (O). These free atoms then combine with other oxygen molecules to form ozone:
$$O_2 \xrightarrow{UV} O + O$$
$$O + O_2 \rightarrow O_3 \text{ (Ozone)}$$
Chemicals responsible for depletion:
Chlorofluorocarbons (CFCs), used as refrigerants and in fire extinguishers.
Two harmful consequences:
- Increased UV radiation reaching Earth causes skin cancer in humans.
- UV radiation is highly damaging to all living organisms/ecosystems.
Source: Chapter 13, Section 13.2.1
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Explanation
- Examiners expect the two chemical equations for ozone formation — writing them earns key marks.
- "CFCs" must be written in full at least once: Chlorofluorocarbons.
- The textbook explicitly mentions skin cancer as a consequence; always include it. For the second consequence, any reference to harm to organisms/UV damage is acceptable.
- Do not confuse ground-level ozone (pollutant) with stratospheric ozone (protective layer).