Compare pollution controls and explain ozone depletion
Match air-pollution controls to pollutant chemistry and explain the evidence and mechanism for ozone depletion.
Exam scope and assessment notes
Original StudyForA teaching and practice, not Cambridge-authored questions, mark schemes or official grades. Cambridge expects candidates to study all eight topics, carry out investigative work and learn teacher-selected case studies. This course does not replace a centre's named case-study examples, current local environmental data, supervised fieldwork or the candidate's own investigation. Practice datasets are illustrative, not observations from a real place. No official assessment or certification is provided. The examples and practice datasets in these lessons are fictional and formative; learners must add their centre's verified case studies and current local evidence.
Before you begin
- Cambridge recommends prior environmental/science study equivalent to IGCSE or O Level. This is an AS-only qualification; use the exam-year syllabus and confirm centre entry details.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What makes environmental evidence useful?
What you will learn
- Match flue-gas desulfurisation, catalytic converters and precipitators to pollutants
- Explain CFC movement and ultraviolet breakdown in the stratosphere
- Describe how hypotheses gain support through further research and corroboration
Controls must match the pollutant
Reducing fossil-fuel use can lower several emissions. Fuel or flue-gas desulfurisation targets sulfur dioxide; catalytic converters reduce oxides of nitrogen; electrostatic precipitators capture particulates. Safe household-product use, storage and disposal can limit VOCs. Vehicle restrictions, legislation and the polluter-pays principle change incentives.
Evaluate compliance, monitoring, cost and whether pollution shifts to another source or location. Use the named control for the pollutant in the question; a particle filter does not remove every gas.
Ozone depletion is distinct from climate change
Chlorofluorocarbons can reach the stratosphere, where ultraviolet light releases chlorine that catalytically destroys ozone. The syllabus also uses the ozone hole threshold of average concentration below 100 Dobson Units and asks why depletion is greatest over Antarctica, including the polar vortex, polar stratospheric clouds and temperature.
Ozone depletion increases ultraviolet exposure, affecting human health, crops, ecosystems and materials. International agreements have reduced and phased out ozone-depleting substances; alternatives such as HCFCs and fluorinated gases can have environmental impacts. The Rowland–Molina hypothesis illustrates how later experimental and observational evidence supported an initially disputed mechanism. Evaluate agreements and alternatives without assuming they have no trade-offs.
Sources for this lesson
Pause and explain
In which atmospheric layer is the ozone layer located?
Worked example
A factory lowers particulate emissions but sulfur dioxide remains high. Select another control and explain why the first may not solve both problems.
Show the worked solution
- Identify the remaining pollutant.
- Select a sulfur-specific control.
- Explain that controls depend on pollutant chemistry.
Answer Fuel or flue-gas desulfurisation targets sulfur dioxide. An electrostatic precipitator removes particles but does not automatically remove gaseous sulfur dioxide, so controls should be matched to pollutant chemistry and monitored separately.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how a CFC released near the surface can contribute to ozone depletion.
Give me a hint
Trace transport, photodissociation and chlorine chemistry.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply match flue-gas desulfurisation, catalytic converters and precipitators to pollutants to the stated context.
- Explain the inference and one limitation or trade-off.
CFCs can persist through the troposphere and reach the stratosphere. Ultraviolet light breaks them down, releasing chlorine radicals that participate in reactions converting ozone to oxygen. The mechanism involves catalytic cycles.
Look for these in your work
- Match flue-gas desulfurisation, catalytic converters and precipitators to pollutants
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
A city uses electrostatic precipitators and vehicle restrictions. Which problems do these target, and what remains to assess?
Give me a hint
Different measures affect different sources and pollutants.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply explain cfc movement and ultraviolet breakdown in the stratosphere to the stated context.
- Explain the inference and one limitation or trade-off.
Precipitators capture charged particles from industrial exhaust; vehicle restrictions can reduce traffic emissions and exposure in controlled zones. Assess other sources, compliance, displacement to nearby streets and monitored air quality.
Look for these in your work
- Explain CFC movement and ultraviolet breakdown in the stratosphere
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
How did later research help assess an initially disputed ozone-depletion hypothesis?
Give me a hint
Explain the path from mechanism to corroborating evidence.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply describe how hypotheses gain support through further research and corroboration to the stated context.
- Explain the inference and one limitation or trade-off.
Researchers proposed that CFC breakdown releases chlorine that depletes stratospheric ozone. Later observations and experiments tested related predictions and supported the mechanism. Confidence increased through converging evidence, not simply because an early paper asserted it.
Look for these in your work
- Describe how hypotheses gain support through further research and corroboration
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Common mistakes
- Confusing ozone depletion with the enhanced greenhouse effect
- Using a particle filter as a control for every pollutant
- Presenting science as one experiment proving a theory
What can you explain now?
In which atmospheric layer is the ozone layer located?
Compare with the explanation
The stratosphere
The syllabus links ozone depletion there to CFC chemistry under ultraviolet light.
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Make it stick
How is ozone depletion mechanistically different from the enhanced greenhouse effect?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.