The atmosphere, greenhouse gases and pollution
The air today is very different from Earth's early atmosphere. This topic covers how it changed, why some gases trap heat, how human activity adds to them, and the pollutants made when we burn fuels.
Part 1 of 3: Learn it
In short
- Today's air is about four-fifths nitrogen and one-fifth oxygen, with small amounts of argon, carbon dioxide and water vapour.
- Oxygen built up because algae, and later plants, photosynthesised; carbon dioxide fell as it was locked into rocks and fossil fuels and dissolved in the oceans.
- Carbon dioxide, methane and water vapour are greenhouse gases.
Where this is in your specification
Spec points: AQA 4.9.1 to 4.9.3 (Combined Trilogy 5.9), Edexcel Topic 8, OCR C6.3 (J250 C6.2)
| Board | Topic: The atmosphere and using resources |
|---|---|
| AQA 8462 | 4.9 and 4.10 (8462); 5.9 and 5.10 (8464) |
| Edexcel 1CH0 | Topics 2, 4 and 8 (1CH0 also Topics 5 and 9) |
| OCR J248 | C6.1 and C6.3 (J250: C6.1 and C6.2) |
| Eduqas C410 | 11, 12 |
| Cambridge IGCSE 0620 | 10.1 to 10.3 |
| National 5 C813 75 | 3(c) Fertilisers |
The early atmosphere
Scientists think intense volcanic activity in Earth's first billion years released mostly carbon dioxide, with water vapour and nitrogen and small amounts of methane and ammonia, and very little oxygen. As the Earth cooled, the water vapour condensed to form the oceans.
Evidence is limited because this happened billions of years ago, so these ideas are models that can change.
How it changed
- Carbon dioxide dissolved in the oceans, and some formed carbonate rocks on the sea floor.
- Algae, and later plants, used carbon dioxide in photosynthesis and released oxygen.
- Carbon was locked away in sedimentary rocks such as limestone and in fossil fuels: coal, crude oil and natural gas.
The greenhouse effect
The Sun's short-wavelength radiation passes through the atmosphere and warms the Earth's surface. The surface gives out longer-wavelength infrared radiation. Greenhouse gases absorb some of that infrared and re-emit it in all directions, including back towards the surface, which keeps the Earth warm enough for life.
Human activities add more: burning fossil fuels and deforestation raise carbon dioxide; cattle farming, rice fields and landfill raise methane. Most climate scientists agree that this is causing global temperatures to rise, with effects such as rising sea levels, more extreme weather and changes to where species can live.
Pollutants from fuels
| Pollutant | Source | Effect |
|---|---|---|
| Carbon monoxide | incomplete combustion | toxic, colourless and odourless; reduces the oxygen blood can carry |
| Soot (particulates) | incomplete combustion | global dimming and lung damage |
| Sulfur dioxide | sulfur impurities in fuels | acid rain and breathing problems |
| Oxides of nitrogen | nitrogen and oxygen reacting in hot engines | acid rain and breathing problems |
Name the two main gases in today's atmosphere and give their rough proportions.
Show the answer
Nitrogen, about 78% (four-fifths), and oxygen, about 21% (one-fifth).
Part 2 of 3: See it worked
Worked examples
Example 1
About how much oxygen is in a 500 cm³ sample of dry air?
- Oxygen is about 21% of the air
- 0.21 × 500 = 105
Answer: About 105 cm³.
Example 2
Explain how an increase in carbon dioxide in the atmosphere can raise the Earth's temperature.
- Radiation from the Sun warms the surface, which emits infrared radiation
- Carbon dioxide absorbs some of that infrared and re-emits it, some back towards the Earth
- More carbon dioxide means more energy is kept in the lower atmosphere
Answer: More infrared radiation is absorbed and re-emitted towards the surface, so less escapes to space and the average temperature rises.
Common mistakes
- Saying the early atmosphere was mostly oxygen. It had very little.
- Mixing up the greenhouse effect with the hole in the ozone layer.
- Saying carbon monoxide causes acid rain. Sulfur dioxide and nitrogen oxides do.
- Saying greenhouse gases reflect radiation. They absorb and re-emit it.
Give two human activities that increase the amount of methane in the air.
Show the answer
Any two of: cattle farming, rice growing, landfill sites.
Part 3 of 3: Test yourself
Check yourself
Answer each one in your head or on paper first, then open it to check.
Name the two main gases in today's atmosphere and give their rough proportions.
Nitrogen, about 78% (four-fifths), and oxygen, about 21% (one-fifth).
Give two human activities that increase the amount of methane in the air.
Any two of: cattle farming, rice growing, landfill sites.
Why is carbon monoxide dangerous?
It is toxic, cannot be seen or smelled, and reduces the amount of oxygen the blood can carry.
Jobs that use this
- Meteorologist (se abre en otra pestaña)
- Chemist (se abre en otra pestaña)
- Ecologist (se abre en otra pestaña)
Each link opens the job profile on the National Careers Service (England). In the rest of the UK: My World of Work (Scotland), Careers Wales, nidirect careers (Northern Ireland).
Estos apuntes están en inglés porque siguen los programas de examen del Reino Unido.
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