C9 - Chemistry of the Atmosphere

• The proportions of different gases in the atmosphere

  • Approximately 80% is Nitrogen
  • Approximately 20% is Oxygen
  • Small proportions of various other gases, including carbon dioxide, water vapour and noble gases.
• The Earth's Early Atmosphere

  • Evidence is limited because of the time scale of 4.6 billion years and theories have changed/developed over time
• Theory of the Earth's Early Atmosphere

  -> There was intense volcanic activity that released gases that formed the early atmosphere

  • At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus today: mainly CO2 with little or no O2
  • Volcanoes also produced nitrogen N2 which gradually built up in the atmosphere & there may have been small proportions of methane CH4 and ammonia NH3

  -> Water vapour condensed to form the oceans

  • CO2 dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of CO2 in the atmosphere
• How Oxygen Increased

  ->Algae & plants produced the O2 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 % oxygen gradually increased to a level that enabled animals to evolve
• How Carbon Dioxide Decreased

  • Algae and plants decreased the % CO2 in the atmosphere by photosynthesis
  • CO2 was also decreased by the formation of sedimentary rocks that contain carbon (e.g. limestone and coal) and by the production of fossil fuels from the remains of dead plants and animals when they decayed
• Greenhouse gases

  • Maintain temperatures on earth high enough to support life
  • These include CO2 and CH4 ( Methane )
• The Greenhouse Gas Effect

  • Electromagnetic radiation at most wavelengths (both long and short) from the sun passes through the Earth’s atmosphere
  • The Earth absorbs some radiation and thus warms up (essential for life on Earth). But some heat is radiated from the Earth as infrared radiation.
  • Some of this IR radiation is absorbed by greenhouse gases in the atmosphere
  • Atmosphere warms up leading to the greenhouse effect and global warming
• Human activities which contribute to an increase in greenhouse gases in the atmosphere

  • Driving
  • Consuming Electricity
  • Raising Livestock
  • Decay of organic waste in landfill sites
• What do Scientists believe Human Activity will result in?

  • 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.
  • As a result, this leads to simplified models, opinions and speculations presented in the media which are based on PARTS of the evidence which may be BIASED
• Global climate change

  • An increase in average global temperature is a major cause of climate change.
• Possible Effects of Global Climate Change

  • Extinction of Species
  • Raising sea levels due to the melting of polar ice caps
  • Migration - People will move from areas suffering with droughts and floodings
  • Decrease in crop yield for all major world crops
• Carbon Footprint

  • 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.
• How can we reduce a carbon footprint?

  • It can be reduced by reducing emissions of carbon dioxide and methane e.g. by using less electricity (so using less fossil fuels or using an alternative source of electricity)
  • By reducing the amount of travel or transportation (of either goods or people)
  • Planting more trees.
• How may action be limited when reducing a carbon footprint?

  ->Action may be limited because:

  • Economy is dependent on fossil fuels
  • Renewable energy is usually more expensive than burning fossil fuels
  • Having international agreements are difficult as they don't want to sacrifice their economy
  • Not enough education for individuals as to why lifestyle changes are necessary
• Combustion of Fuels

  • Combustion of fuels is a major source of atmospheric pollutants
  • Most fuels contain carbon and/or hydrogen and may also contain some sulfur.
• How is pollution caused by combustion?

  • The gases released into the atmosphere when a fuel burns may include carbon dioxide, water vapour, carbon monoxide, and oxides of nitrogen
  • Solid particles and unburned hydrocarbons may also be released, forming particulates in the atmosphere
• Incomplete Combustion

  • If there’s not enough oxygen, some of the fuel doesn’t burn – this is incomplete combustion
  • Here, solid particles of soot (carbon), carbon monoxide and unburnt fuel are released.
• What are the issues regarding Sulfur Dioxide and Oxides of Nitrogen?

  • Sulfur dioxide and Oxides of Nitrogen can cause respiratory problems in humans
  • Causes acid rain which damages buildings and plants
• What problems do particulates cause?

  • Particulates cause global dimming by reducing sunlight and causes health problems by damaging lungs
• Particulates

  • Solid carbon particles / Soot (or Particulates) is released during incomplete combustion
• Global Warming vs Climate Change

  • Refers to the overall increase in the Earth's temperature
  • Climate Change is a consequence of Global warming and refers to the effects on the climate e.g. Large-scale shifts in weather patterns
• is coal formed?

  • Formed from remains of ferns and trees -> If they die in wetlands, then they do not decompose due to a lock of oxygen and acidic conditions which prevents bacteria from carrying out decomposition
  • Over time, the plant remains are covered in sediment and compressed -> High temperatures and pressure creates coal
• How are oxides of nitrogen formed?

  • Nitrogen from air reacting with oxygen at HIGH TEMPERATURES in car engines