GCSE Chemistry The Atmosphere Notes
Today's atmosphere is roughly 78% nitrogen and 21% oxygen. Human activity is now changing its composition, causing climate change.
Key concepts
- Greenhouse effect
- Greenhouse gases absorb outgoing infrared radiation and re-emit it, warming Earth's surface.
- Greenhouse gases
- Carbon dioxide, methane and water vapour — all absorb infrared radiation.
- Combustion pollutants
- CO (incomplete combustion), soot, SO₂ and NOₓ — cause health and environmental problems.
- Modern air: ~78% N₂, ~21% O₂, ~1% argon, ~0.04% CO₂ and variable water vapour.
- Rising CO₂ from burning fossil fuels enhances the greenhouse effect and warms the planet.
- SO₂ and NOₓ dissolve in rain to form acid rain, damaging plants, buildings and aquatic life.
Worked example
Explain how burning fossil fuels contributes to global warming.
- 1Fossil fuels contain hydrocarbons that release CO₂ when burned.
- 2CO₂ is a greenhouse gas that absorbs infrared radiation emitted from Earth's surface.
- 3This traps energy in the lower atmosphere.
- 4The average global temperature therefore rises, causing climate change.
Answer: Extra CO₂ from combustion traps more infrared radiation, warming the atmosphere.
Common mistakes
✗ Confusing the greenhouse effect with the ozone hole.
✓ They are different issues — one traps IR; the other lets more UV through.
✗ Saying CO₂ 'reflects' heat.
✓ It absorbs and re-emits infrared radiation.
✗ Mixing up pollutants.
✓ CO = toxic gas from incomplete combustion; SO₂ / NOₓ = acid rain.
Quick check
Try these, then reveal the answers.
Two main gases in the atmosphere?Reveal answer
Nitrogen and oxygen.
Give two greenhouse gases.Reveal answer
Carbon dioxide and methane.
Which pollutant causes acid rain?Reveal answer
Sulfur dioxide (SO₂) and nitrogen oxides (NOₓ).
Exam tips
- Link greenhouse gas → absorbs IR → re-emits → warms surface, for full marks.
- Distinguish between the greenhouse effect (essential for life) and enhanced greenhouse effect (climate change).
- Use precise pollutant names — CO not just 'carbon'.
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Frequently asked questions
Why is the greenhouse effect a problem now?+
Human activity has increased the concentration of greenhouse gases, especially CO₂, enhancing the natural effect and raising global temperatures.
What causes acid rain?+
Sulfur dioxide and nitrogen oxides from burning fossil fuels dissolve in water in the atmosphere to form acidic solutions that fall as rain.
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