Explain atmospheric pollution and exposure
Trace air pollutants from sources to environmental and health impacts, using concentration, exposure and monitoring evidence.
Section 7.1 · Acid deposition
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
- Describe sources and impacts of sulfur dioxide, nitrogen oxides, particulates and VOCs
- Explain how weather, terrain and settlement affect exposure
- Distinguish emissions from measured concentrations and health outcomes
Explain acid deposition and photochemical smog
Acid deposition is acidic wet deposition with pH below 5.6 (rain, snow, hail or fog) or dry deposition (dust and gases). Sulfur dioxide from burning sulfur-containing fuels can react with oxygen and water to form sulfuric acid; nitrogen monoxide from hot engines can react further to form nitric acid. Acid deposition can affect fish gills and populations, defoliate vegetation and reduce crops, and chemically weather stone and brick.
Photochemical smog forms when oxides of nitrogen and volatile organic compounds react in sunlight, producing a mixture of pollutants and particulates including ground-level ozone. It can irritate eyes and respiratory systems, lower crop yields and damage plastics and rubber. These processes are different from stratospheric ozone depletion.
Follow exposure and management
Combustion, transport, industry, agriculture and household products can release sulfur dioxide, oxides of nitrogen, particulates and volatile organic compounds. Wind, temperature inversions, topography, rainfall and settlement patterns influence concentration; emissions are not the same as exposure.
Record site, time, instrument, units and averaging period. One reading may not represent annual exposure; compare with a suitable baseline or standard and use aggregate health data carefully.
Make measurements comparable
Record site, time, instrument, units and averaging period. One reading may not represent annual exposure; compare with a suitable baseline or standard.
Case studies should identify a named event and place, impacts and management strategies. Health claims need suitable aggregate data and careful handling of privacy and causation.
Sources for this lesson
Pause and explain
What is the difference between emission and exposure?
Worked example
Particulate readings rise beside a road at rush hour but are lower at a park monitor. Explain two possible causes and one limit.
Show the worked solution
- Compare traffic timing and source proximity.
- Consider wind, barriers and monitor placement.
- State what one set of readings cannot establish.
Answer Traffic and proximity may contribute to higher rush-hour readings near the road. Wind, street-canyon effects and monitor placement may also explain the difference. These readings alone do not establish long-term exposure or health effects; repeated calibrated measurements and context are needed.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
A city installs catalytic converters and nitrogen dioxide falls at one station. What supports an intervention claim?
Give me a hint
Check repeated readings, other sources and comparison.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply describe sources and impacts of sulfur dioxide, nitrogen oxides, particulates and vocs to the stated context.
- Explain the inference and one limitation or trade-off.
Use repeated calibrated measurements at multiple locations with traffic and weather records. A baseline or comparison area helps separate the intervention from other source changes or weather effects.
Look for these in your work
- Describe sources and impacts of sulfur dioxide, nitrogen oxides, particulates and VOCs
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
A temperature inversion occurs during a pollution episode. Explain how it can affect near-surface concentration.
Give me a hint
Consider vertical mixing.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply explain how weather, terrain and settlement affect exposure to the stated context.
- Explain the inference and one limitation or trade-off.
A warmer layer above cooler surface air limits vertical mixing. Pollutants can remain concentrated near the ground until conditions change or emissions are reduced.
Look for these in your work
- Explain how weather, terrain and settlement affect exposure
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Hospital admissions rise during a pollution episode. What should an investigation check before making a causal claim?
Give me a hint
Temporal association is a signal, not proof.
Compare my reasoning
- Identify the relevant data, place or process in the prompt.
- Apply distinguish emissions from measured concentrations and health outcomes to the stated context.
- Explain the inference and one limitation or trade-off.
Check timing and pollutant measurements, but also account for weather, infections, age structure and healthcare access. Use appropriate aggregate health data, protect privacy and compare against a suitable baseline.
Look for these in your work
- Distinguish emissions from measured concentrations and health outcomes
- Uses relevant evidence and explains the environmental mechanism
- Distinguishes observation, inference and limitation
Common mistakes
- Treating emissions as identical to exposure
- Using one monitor reading as a trend
- Claiming a health outcome was caused by one pollutant from correlation alone
What can you explain now?
What is the difference between emission and exposure?
Compare with the explanation
An emission is released at a source; exposure is concentration experienced at a place and time
Transport and local conditions can change the concentration people experience.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Why does an emissions inventory not directly measure human exposure?
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.