1. Chemistry of the Atmosphere
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23/04/2019
Chemistry of the Atmosphere
AQA 2016 Chemistry topic 9
W Richards
The Weald School

2. 9.1 The Composition and Evolution of the Atmosphere
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9.1 The Composition and Evolution of the Atmosphere

3. The Earth’s Atmosphere
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For the last 200 million years the atmosphere has remained roughly the same – it contains 78% nitrogen, 21% oxygen, 1% noble gases and about 0.03% CO2
Carbon dioxide, water vapour
Oxygen
Nitrogen
Noble gases

4. Evolution of the Earth’s Atmosphere
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Carbon
dioxide
Methane
Ammonia
Oxygen
Nitrogen
Others
The early atmosphere was like the present-day atmosphere of Venus or Mars
4 Billion years
3 Billion years
2 Billion years
1 Billion years
Present day

5. Evolution of the Earth’s Atmosphere
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Volcanic activity releases nitrogen, CO2, methane, ammonia and water vapour into the atmosphere. The water vapour condenses to form oceans.
Evidence for the early atmosphere is limited. Why is that?
4 Billion years
3 Billion years
2 Billion years
1 Billion years
Present day
Carbon from CO2 becomes locked up in sedimentary rocks as carbonates and fossil fuels. As the oceans form by condensing water vapour the carbonates and fossil fuels become locked underground, decreasing the amount of CO2.

6. Changes in Oxygen and CO2
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Somewhere around 2.7 billion years ago, algae and plants arrived and started taking in carbon dioxide and producing oxygen. A billion years later, there was enough oxygen for animals to evolve.
4 Billion years
3 Billion years
2 Billion years
1 Billion years
Present day
Q. What are the equations for photosynthesis?
Carbon dioxide + water glucose + oxygen
6CO H20 C6H12O O2
Sunlight
Chlorophyll

7. Decreasing Carbon Dioxide
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As well as photosynthesis by plants and algae, atmospheric carbon dioxide levels were also decreased by the formation of carbonate rocks, e.g.:
Chalk
Limestone
Marble (made from chalk or limestone)

8. Formation of oil and gas
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1) Layers of dead sea _____ settle on the seabed.
2) Layers of __________ rock build up on top.
3) The heat and ________ from these rocks, along with the absence of ______, mean that oil and gas are formed over ______ of years.
Words – sedimentary, millions, oxygen, creatures, pressure

9. 9.2 Carbon Dioxide and Methane as Greenhouse Gases
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9.2 Carbon Dioxide and Methane as Greenhouse Gases

10. Carbon Dioxide and Global Warming
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Global levels of Carbon Dioxide in PPM
Is there a link?

11. The Greenhouse Effect
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1) Heat and light energy reach us from the sun (higher wavelengths such as visible light)…
3) …some of the heat escapes back into space…
4) …while some of it is reflected back to the Earth by a layer of greenhouse gases (water vapour, CO2 and methane) – this is called The Greenhouse Effect
2) …a lot of this heat is reflected off the Earth’s surface as lower wavelength infra red…

12. What problems do these next pictures show?
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What problems do these next pictures show?

13. 23/04/2019

14. Humans Causing Greenhouse Gases
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How do the following activities affect the amount of greenhouse gases in the atmosphere?
Excessive burning of fossil fuels…
Large scale deforestation…
3) Large scale cattle farming

15. Carbon Dioxide and Global Warming
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Global levels of Carbon Dioxide in PPM
Many scientists believe that human activities will cause global warming.
What reasons would people have for believing this?
What reasons would stop people believing global warming is happening?

16. Effects of Global Climate Change
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What possible effects of climate change do these pictures show?

17. Carbon Footprint
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The “carbon footprint” is defined as the total amount of carbon dioxide and other greenhouse gases emitted over the full cycle of a product or event.
Q. Consider the humble plastic bag. What steps are involved in its life cycle and how can the carbon footprint of each step be reduced?
Steps in the bag’s life cycle
Ways to reduce the footprint
Drill for crude oil
Put the oil through fractional distillation
Crack alkanes to make ethene
Use heat to polymerise ethene
Transport plastic bags to shops
Transport bags to landfill sites
Use recycled materials
Reduce consumption of the bags
Manufacture them closer to shops
Recycle the bags after use

18. Other ways to reduce the footprint
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Here are some other ways to reduce the carbon footprint:
Use better insulation
Offset with renewable energy
Increase recycling
What factors might limit these options?
Carbon capture
Personal choice

19. 9.3 Common Atmospheric Pollutants and their Sources
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9.3 Common Atmospheric Pollutants and their Sources

20. Pollution Some examples of pollution…
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Some examples of pollution…
Carbon dioxide, water vapour, carbon monoxide are caused by the burning of ____ _____. Carbon monoxide is a ____ gas and is not easily detected due to being ________.
Sulfur dioxide and nitrogen dioxide cause ____ ____ which damages trees and buildings and _________ problems in humans.
Particulates (unburned _______) can make buildings dirty and worsen breathing difficulties and cause global ______.
Words – hydrocarbons, dimming, fossil fuels, odourless, acid rain, respiratory, toxic

21. Combustion of Fuels Lots of oxygen: Some oxygen: Methane Oxygen +
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Lots of oxygen:
Methane
Oxygen +
Carbon dioxide
Water +
Water + O H
Methane C H
Oxygen + O C O
Some oxygen:
Carbon monoxide

22. Other products of burning fuels
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Sulphur dioxide
Sulphur dioxide: S O
Sulphur
Oxygen +
Nitrogen monoxide N O
Oxygen + O
Nitrogen N
Nitrogen monoxide: O
Oxygen +
Nitrogen monoxide N
Nitrogen dioxide N O
Nitrogen dioxide:

23. Incomplete Combustion
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As well as producing carbon monoxide, incomplete combustion can also produce soot:
Little oxygen: C H
Methane O
Oxygen +
Water
Carbon
“Soot”