Unit 7: Atmospheric Pollution focuses on the causes, types, effects, and mitigation of air pollution. On the APES exam, this unit is heavily tested in both MCQs and FRQs, often in the context of human health, ecosystem impacts, and pollution control strategies.
This RevisionDojo review breaks down everything you need to know.
🌫 Key Topics in Unit 7
- Types of air pollutants (primary vs. secondary)
- Sources of air pollution
- Smog formation (photochemical vs. industrial)
- Acid deposition
- Indoor air pollution
- Air pollution control technologies
- Laws and regulations (Clean Air Act, Kyoto Protocol, etc.)
🛑 Primary vs. Secondary Pollutants
Primary pollutants: Directly emitted into the atmosphere
- Examples: CO, SO₂, NOx, particulate matter (PM), VOCs
Secondary pollutants: Formed in the atmosphere through chemical reactions
- Examples: Ozone (O₃) in photochemical smog, sulfuric acid in acid rain
☀️ Photochemical Smog
- Caused by: Sunlight + NOx + VOCs
- Location: Common in sunny, urban areas with lots of traffic
- Main pollutant: Ground-level ozone (O₃)
- Impacts: Respiratory problems, crop damage, reduced visibility
🏭 Industrial Smog
- Caused by: Burning coal → SO₂ + particulates
- Location: Industrial cities, especially in cold/damp climates
- Impacts: Respiratory illness, reduced sunlight
🌧 Acid Deposition (Acid Rain)
- Formation: SO₂ & NOx → acids in precipitation
- Effects: Damages forests, acidifies lakes, corrodes buildings
- Solutions: Reduce SO₂ and NOx emissions, switch to cleaner fuels
🏠 Indoor Air Pollution
- Common sources:
- Radon (naturally occurring radioactive gas)
- Asbestos (insulation material)
- Tobacco smoke
- VOCs from paints/cleaners
- Biomass burning in poorly ventilated homes
- Health impacts: Lung cancer, respiratory diseases, headaches
🛠 Air Pollution Control Technologies
- Catalytic converters – Reduce CO, NOx, VOCs in cars
- Scrubbers – Remove SO₂ from coal plant emissions
- Electrostatic precipitators – Remove particulates from smokestacks
📜 Key Laws & Agreements
- Clean Air Act (U.S.) – Sets limits on major pollutants, established National Ambient Air Quality Standards (NAAQS)
- Montreal Protocol – Phased out CFCs to protect the ozone layer
- Kyoto Protocol / Paris Agreement – International climate change agreements
🧠 APES Exam Tips for Unit 7
- Memorize the differences between primary and secondary pollutants.
- Be able to explain smog formation with a diagram.
- Know key pollution control devices and how they work.
- Be prepared to analyze pollution data trends in FRQs.
💡 FAQ – Unit 7: Atmospheric Pollution
Q: Why is ozone good in the stratosphere but bad at ground level?
A: In the stratosphere, ozone protects from UV radiation. At ground level, it’s a harmful pollutant causing respiratory issues.
Q: What’s the biggest source of NOx in the U.S.?
A: Motor vehicle emissions.
Q: Which law saved the ozone layer?
A: The Montreal Protocol (1987).
Final Word from RevisionDojo:
Unit 7 is all about understanding pollution sources, effects, and solutions. On the APES exam, you’ll often be asked to propose mitigation strategies — make sure your answers link the strategy directly to the pollutant it reduces.
