C9 - Chemistry of the atmosphere

• The proportions of different gases in the atmosphere

  For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:

  • about 80 % nitrogen
  • about 20 % oxygen
  • small proportions of various other gases, including carbon dioxide, water vapour and noble gases.
• The earth's early atmosphere - theories

  Theories about what was in the Earth’s early atmosphere and how the atmosphere was formed have changed and developed over time. Evidence for the early atmosphere is limited because of the time scale of 4.6 billion years.
• Earth early atmosphere - Volcanic activity

  • One theory suggests that during the first billion years of the Earth’s existence there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans.
  • At the start of this period the Earth’s atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas.
  • Volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia.
• Earth early atmosphere - oceans

  When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of carbon dioxide in the atmosphere. 
• How did oxygen increase?

  Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis.

  Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere. Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve.
• How carbon dioxide decreased?


  Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon.
• Describe and explain the formation of deposits of limestone, coal, crude oil and natural gas.

  Over millions of years, heat and pressure turned the dead material into fossil fuels (coal, crude oil and natural gas) or limestone. Coal is a fossil fuel which is formed from dead trees. The dead trees were buried by flooding, which prevented oxidation of the wood taking place due to a lack of oxygen.
• Greenhouse gases

  Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life. Water vapour, carbon dioxide and methane are greenhouse gases.
• Describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter.

  1. electromagnetic radiation at most wavelengths passes through the Earth's atmosphere
  2. the Earth absorbs most of the radiation and warms up
  3. the Earth radiates energy as infrared radiation
  4. some of the infrared radiation goes into space
  5. some of the infrared radiation is absorbed by greenhouse gases in the atmosphere
  6. the lower atmosphere warms up

  
• What human activities increase the amount of greenhouse gasses in the atmosphere?

  Burning fossil fuels, deforestation, agriculture, driving
• Climate change - scientific predictions

  Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change.

  However, it is difficult to model such complex systems as global climate change. This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.
• Global climate change effects

  The climate describes the average weather over a long time and over a large area. The enhanced greenhouse effect is leading to climate change. The effects of this include:

  • glaciers and polar ice melting
  • sea levels rising
  • rainfall changing, producing floods or droughts
  • habitats changing
• Carbon footprint and its reduction

  The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.The carbon footprint can be reduced by reducing emissions of carbon dioxide and methane.
• Ways to reduce carbon footprint

  There are international treaties aimed at reducing the emissions of carbon dioxide and other greenhouse gases. However, even if these emissions could fall significantly, it would take a long time for the Earth’s temperature to stabilise then decrease.
• Ways to mitigate the effects of climate change

  These include:

  • building flood defences to manage floods from rivers and seas
  • building irrigation systems to provide water in droughts
  • planting different crops, better adapted to a new climate

  These steps are expensive, need to be on a large scale, and may themselves harm the environment.
• Atmospheric pollutants from fuels

  The combustion of fuels is a major source of atmospheric pollutants.Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur.The gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen. Solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere.
• Describe how carbon monoxide, soot (carbon particles), sulfur dioxide and oxides of nitrogen are produced by burning fuels

  • Carbon monoxide, CO - Incomplete combustion of any fuel containing carbon atoms
  • Particulate carbon, C (soot) - Incomplete combustion of any fuel containing carbon atoms
  • Unburned hydrocarbons - Hydrocarbon fuel molecules which have not been oxidised at all
  • Sulfur dioxide, SO2 - Combustion of a fossil fuel which contains sulfur impurities
  • Nitrogen oxides, NOx - Oxidation of atmospheric nitrogen inside the engine of a car, lorry, etc
• Properties and effects of atmospheric pollutants

  • Carbon monoxide is a toxic gas. It is colourless and odourless and so is not easily detected.
  • Sulfur dioxide and oxides of nitrogen cause respiratory problems in humans and cause acid rain.
  • Particulates cause global dimming and health problems for humans.
• Properties and effects of atmospheric pollutants


  • Carbon monoxide is a toxic gas. It is colourless and odourless and so is not easily detected.
  • Sulfur dioxide and oxides of nitrogen cause respiratory problems in humans and cause acid rain.
  • Particulates cause global dimming and health problems for humans.