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Topic 9 Chemistry of the atmosphere By Bethan Poole (9.1 The Composition…
Topic 9 Chemistry of the atmosphere
By Bethan Poole
9.1 The Composition and Evolution of the Earth's atmosphere
9.1.1 The proportions of different gases in the atmosphere :
For 200 million years proportions of gas in atmosphere been the same
Made up of...
78% Nitrogen
21% Oxygen
Small proportions of other gases including Carbon dioxide, water vapour and noble gases
9.1.2 The Earth's early atmosphere
4 billion years ago
Event
Intense volcanic activity produced
Mainly Carbon Dioxide
Water Vapour (condensed to form oceans)
Small amounts of methane and ammonia
Nitrogen
Atmosphere very similar to that on Venus and Mars today
Atmosphere mainly made up of CO2
2.5 billion years ago
Events
Green plants and algae evolve causing
Reduced CO2- Take it in and give out O2
Microorganisms that can't tolerate O2 killed
Carbon becomes locked up in sedimentary rocks
Gases react with O2- produces N2
N2 produced also by bacteria removing nitrates from decaying plant material
Atmosphere mostly CO2, about 25% N2 and about 15% oxygen, Small amounts of other gases
NOW
Atmosphere 78% N2, 21% O2
Amount of CO2 has significantly decreased
Same proportions of gases for about 200 million years
Some water vapour in air
9.1.3 How oxygen increased
Algae and plants photosynthesise
Produces oxygen
Carbon dioxide + water -> Glucose + Oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
Algae started producing oxygen 2.7 billion years ago
Plants evolved over the next billion years- amount of oxygen in atmosphere increased
Oxygen levels eventually increased enough for animals to evolve
9.1.4 How carbon dioxide decreased
Plants and algae evolved
CO2 levels decrease
They take in Carbon Dioxide when they photosynthesise
Sedimentary rocks
Carbon become locked up in sedimentary rocks and fossil fuels
Limestone
Contains Calcium Carbonate
Formed from shells and skeletons
Coal
:
Formed from plant deposits that were buried and compressed over millions of years
Reaction between Carbon Dioxide and Sea Water
Produces
Insoluble Carbonates
Soluble hydrogen carbonates
Too much CO2 in oceans harms marine life
9.2 Carbon Dioxide and methane as greenhouse gases
9.2.1 Greenhouse gases :green_heart:
Greenhouse effect
1) High energy, short wavelength infrared radiation from sun passes through the atmosphere and reaches the earth's surface
2) Some of the radiation is absorbed by the earth
3) But lower energy, longer wavelength infrared radiation is reflected off the earth's surface
4) Greenhouse gases in the Earth's atmosphere absorb the outgoing infrared radiation- increases earth's temperature
Without them...
Earth too cold to support life
Too cold for water to be a liquid
Examples
Carbon Dioxide
Water Vapour
Methane
9.2.2 Impact of Human activity
Human activities can increase the levels of CO2 + methane in atmosphere
Burning of fossil fuels
Fossil fuels contain carbon that's been locked up for millions of years - burning releases CO2
Amount of CO2 has increased over last 100 years- correlates to the amount of fossil fuels burnt
Deforestation
Fewer trees taking in CO2
Tree are a carbon store- when burnt release CO2
Other factors
Decomposition of rubbish in landfill sites
Increase in animal farming
Many scientist believe increase in greenhouse gases will increase temp of Earth's surface
Models + the Media
Understanding the Earth's climate fully is hard because
It's complex
There are many variables so hard to make a model that's not oversimplified
Led to speculation on the links between CO2 and climate change particularly in the media
Peer Review
1) Scientists come up with a hypothesis and test it
2) They share their finding in peer review journals or at conferences
Peer review
where other scientists check the results and the scientific explanations before they're published
3) If not correct, hypothesis can be modified or scrapped
9.2.3 Global climate change :warning:
If average global temp. increases global climate change could happen
Can cause
Rise in sea level (cause devastating floods + coastal erosion)
More frequent and severe storm events
Changes to amount and timing of rainfall
Increased amount of heatwaves
More droughts
Changes to distribution of plants and animals (too hot or cold for them)
Food shortages (amount of food produced by a country will change)
9.2.4 The carbon footprint and its reduction :recycle:
Total amount of Carbon Dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event
For products it includes
Production
Use
Disposal
Can be reduced through
Using more renewable power supplies
Wasting less energy
Carbon capture and storage
Prevents carbon dioxide being released into the atmosphere
Carbon taxes and licences- deters from the use of greenhouse gases
Carbon off-setting, through activities like tree planting
Encouraging the use of carbon-neutral products
Reducing it isn't easy
Due to....
Disagreements over causes and consequences of climate change
Lack of info and knowledge in general public
Reluctance of people to change lifestyle
Economic considerations (expensive to produce electricity from other sources)
Disagreement between countries on what to do
9.3 Common atmospheric pollutants and their sources
9.3.1 Atmospheric pollutants from fuels + 9.3.2 Properties and effects of atmospheric pollutants
Combustion of fuel= major source of atmospheric pollutants
When burnt gases are released into atmosphere including CO2, water vapour, CO, sulphur dioxide and nitrogen oxides
Carbon dioxide
Complete Combustion
Made when methane reacts with lots of oxygen
methane + oxygen -> carbon dioxide + water
CH4 + 2O2 -> CO2 + 2H2O
Useful- Greenhouse gas- maintains temp. on earth
Dangerous- Contributes to global warming- greenhouse gas
Reduce by reducing amount of fossil fuels burnt
Carbon Monoxide + Particulate Carbon (soot)
Incomplete combustion
Made when methane reacts with a bit of oxygen
methane + oxygen -> carbon monoxide + water + carbon
3CH4 + 4O2 -> 2CO + 6H2O + C
Soot pollutes the air making it black
Carbon monoxide bad- causes respiratory problems- binds to oxygen in blood
Reduce by making sure combustion is complete
Sulfur Dioxide
Made when sulfur reacts with oxygen
sulfur + oxygen -> sulfur dioxide
S + O2 -> SO2
Sulfur dioxide dissolved in water makes sulphuric acid
Negative- contributes to acid rain- harms plants, animals, erodes buildings
Reduce by taking out impurities before burning it
Nitrogen oxides
made when nitrogen reacts with oxygen
Nitrogen + Oxygen -> Nitrogen monoxide
N2 + O2 -> 2NO
Nitrogen monoxide + oxygen -> nitrogen dioxide
2NO + O2 -> 2NO2
Nitrogen oxides dissolve in water to make nitric acid
Negative- contributes to acid rain- harms plants, animals, erodes buildings
Reduce by taking out impurities before burning