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Ozone Layer and Depletion

Explain how stratospheric ozone protects life, how CFCs deplete it and why ultraviolet exposure increases.

  • SEC G3 Pure Chemistry 2027
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Learning objectives

  • discuss the importance of the ozone layer and the problems involved with the depletion of ozone by reaction with chlorine-containing compounds, chlorofluorocarbons (CFCs)

Outcome: explain ozone’s protective role, CFC-driven depletion and the resulting biological risk without confusing the chain with global warming. Prerequisite: distinguish ultraviolet (UV) from infrared (IR) radiation.

1. Definition

The ozone layer is a region of the stratosphere containing ozone that absorbs much harmful ultraviolet radiation.

2. Key Ideas

CFCs can persist to the stratosphere, where ultraviolet radiation releases reactive chlorine species. These species participate repeatedly in ozone-destroying reactions. Less ozone means more harmful UV reaches Earth.

Retrieval check
Which radiation belongs to greenhouse warming? Infrared. Ozone protection concerns ultraviolet.

3. Detailed Explanations

Ozone protects Earth from ultraviolet radiationThe left panel shows a thick ozone layer absorbing most incoming ultraviolet arrows. The right panel shows CFC use leading to a thinner ozone layer and more ultraviolet arrows reaching Earth.Ozone depletion lets more ultraviolet reach EarthIntact ozone layerozone absorbs UVlittle harmful UV reaches EarthCFCs deplete ozonethinner ozone layermore UV reaches Earth
An intact ozone layer absorbs much of the harmful UV. CFC-driven ozone depletion allows more UV to reach Earth.
Atmospheric issueDecisive substanceRadiationConsequence
enhanced greenhouse effectCO₂ and CH₄infraredreduced heat loss and warming
ozone depletionCFC-derived chlorine species reduce O₃ultravioletmore harmful UV exposure

The required causal chain is CFC release → ozone depletion → more UV reaches Earth → increased risk of skin cancer, cataracts and harm to plants or aquatic organisms. Reducing CFC emissions limits additional depletion. Detailed orbital or photochemical kinetics are not required.

4. Common Mistakes

  • Ozone depletion and global warming are not two names for one mechanism.
  • Stratospheric ozone is protective; ground-level ozone is a pollutant.
  • Ozone absorbs UV, not outgoing infrared radiation.
  • Reactive chlorine can be regenerated, so one species can affect more than one ozone molecule.

5. Exam Tips

Name the layer, radiation and consequence. “The ozone layer protects Earth” is incomplete unless you say it absorbs harmful ultraviolet radiation.

6. Worked Examples

Modelled example 1

Model: read the protection diagram

Core

Problem

Use the two panels to explain the changed surface exposure.
Study the worked solution

  1. Compare panels

    Method

    The depleted layer absorbs less UV, so more reaches the surface.

    Reason

    The right panel shows more arrows passing through the thinner layer.

    Working

    less O₃ → less UV absorbed → greater surface UV exposure.

Guided practice 2

Guided: changed claim

About 4 min

Problem

A report says ozone fell and surface radiation exposure increased. Which radiation is directly implicated?

Try this before viewing the solution

Radiation

Hints

Hint 1: recall the shield
Identify the radiation that protective stratospheric ozone absorbs.
View solution step by step

  1. Match the atmospheric function

    Method

    Select ultraviolet.

    Reason

    Ozone shielding is separate from greenhouse-gas infrared absorption.

    Working

    ozone loss → more UV reaches Earth.

Challenge 3

Transfer: explain a CFC control

Minimal support

Problem

Why can replacing CFCs reduce future biological risk?

Try this before viewing the solution

Interrupted chain

Hints

Hint 1: trace the ozone chain
Begin with CFC release, then follow ozone abundance and surface ultraviolet exposure.
View complete solution

  1. Trace the interrupted chain

    Method

    Fewer CFCs means fewer ozone-depleting chlorine species reach the stratosphere.

    Reason

    More ozone protection leaves less harmful UV reaching living organisms.

    Working

    lower CFC release → less ozone depletion → lower added UV exposure.

7. Mind Stretchers

Independent: Correct: “CFCs warm Earth because they create a hole that lets infrared radiation in.”

Show answer
The assessed ozone chain is CFC-driven ozone depletion allowing more ultraviolet radiation to reach Earth. Greenhouse warming concerns absorption and re-emission of outgoing infrared radiation by greenhouse gases.

8. Quiz

Practise this lesson
Start focused practice, then practise with more questions across this topic.