Chemistry of the atmosphere

• The Earth was formed roughly 4.6 billion years ago
• For the first billion years of the Earth’s existence, highly active volcanoes populated the surface
• Volcanoes frequently erupted


  This released lots of carbon dioxide
• Early atmosphere


  Carbon dioxide dominated the early atmosphere in a similar way to modern-day Mars and Venus
• Volcanic activity released


  • Nitrogen
  • Water vapour
  • Smaller quantities of methane and ammonia
• The formation of oceans removed carbon dioxide from the atmosphere
• Some of the dissolved carbon dioxide reacted with seawater to produce carbonate precipitates
• Photosynthesis increased the atmospheric concentration of oxygen
• Photosynthesis


  1. Light energy used

  2. Convert carbon dioxide and water into glucose and oxygen
• Algae were the first photosynthetic organisms to evolve approximately 2.7 billion years ago
• Over the next billion years, photosynthesising plants began to evolve
• A threshold concentration of oxygen was reached


  This allowed more complex life forms to evolve, such as animals
• Factors that caused atmospheric carbon dioxide to decrease

  • Oceans
  • Photosynthesis
  • Marine animals
• The formation of oceans removed large amounts of carbon dioxide from the atmosphere
• Carbon dioxide is 1 of the reactants of the equation for photosynthesis
• Marine animals evolved, removing carbonates from the oceans
• Human activities that cause the atmospheric concentrations of greenhouse gases to increase

  • Burning fossil fuels
  • Deforestation
  • Landfill sites
  • Agriculture
• Burning fossil fuels releases carbon, in the form of carbon dioxide
• Fewer trees means less photosynthesis
• Landfill sites are increasing, leading to more decomposition and methane release
• Farm animals release methane during digestion
• Greenhouse effect


  Helps keep the Earth warm enough for life but can cause global warming
• Greenhouse effect process


  1. Sun emits radiation

  2. Earth absorbs some radiation

  3. Long wavelength radiation reflected

  4. Greenhouse gases absorb longer wavelength radiation

  5. Gases re-radiate energy
• The current scientific consensus is that increased greenhouse gas emissions caused by changes to human activity will lead to global climate change
• The global climate system is very complicated
• Some people may have reasons to play down the contribution of greenhouse gas emissions to climate change
• Potential consequences of global climate change

  • Melting of polar ice cap
  • Meteorological events
  • Changes in water availability
  • Changes in precipitation
  • Food shortages
• Melting of polar ice caps

  Causes sea levels to rise, leading to flooding and erosion of coastal regions
• Melting of polar ice caps


  Some species to be less successful hunters
• Changing water availability


  Affects species distributions
• Changes in precipitation


  Regions could receive much less or much more than they are used to
• A carbon footprint is a measure of the total amount of greenhouse gases emitted as a result of a particular service, event or product
• Ways to minimise carbon footprints

  • Maximising energy efficiency
  • Minimising waste
  • Using renewable energy sources
  • Emission-based taxes
  • Emission caps
  • Emissions licenses
  • Carbon capture and storage
  • Carbon off-setting
  • Carbon-neutral products
• Carbon capture and storage captures carbon dioxide before it's released into the atmosphere
• Carbon off-setting compensates emissions by planting trees
• Carbon-neutral products don't change the atmospheric carbon dioxide concentration
• Barriers to reducing carbon footprints

  • Scientific factors
  • Economic factors
  • Political factors
  • Social factors
• Burning fossil fuels is a major cause of air pollution
• Common atmospheric pollutants from fossil fuels

  • Carbon monoxide
  • Particulates
  • Sulfur dioxide
  • Nitrogen oxides
• Incomplete combustion produces carbon monoxide and particulates