Chemistry of the Atmosphere

• what has the atmosphere been like for the last 200 million year

  the proportion of different gases in the atmosphere have been the essentially the same

  • approx 80% nitrogen
  • approx 20% oxygen
  • small proportions of some other gases (e.g. CO2 + H2O) and noble gases
• why is our knowledge of earths early atmosphere limited

  the time scale

  • 4.6B years have passed
  • theories have changed + developed over time
• how do we predict earths early atmosphere was


  in the first billion years of earths existence :

  • there was intense volcanic activity releasing gases forming the early atmosphere
  • we then had a similar atmosphere to mars or venus -> high CO2 levels + tiny or no O2 levels
  • volcanoes also produce N2 that built up in the atmosphere + small proportions of CH4 (methane) + NH3 (ammonia)
  • water vapour then condensed to form oceans
  • CO2 dissolved in the water + carbonates were precipitated producing sediments
  • this reduced the amount of CO2 in the atmospher
• how did levels of oxygen in the atmosphere increase

  algae + plants produced O2 in the atmosphere today through photosynthesis

  -> 6CO2 + 6H2O -> C6H12O6 + 6O2

  • algae first produced oxygen about 2.7B years ago + it soon appeared in the atmosphere
  • over the next billion years plants evolved + the % of oxygen increased to a level enabling animals to evolved
• how did levels of carbon dioxide in the atmosphere decrease


  algae + plants decreased CO2 through photosynthesis

  -> 6CO2 + 6H2O -> C6H12O6 + 6O2

  • CO2 also decreased through the formation of sedimentary rocks that contain carbon (e.g. limestone + coal) + through the production of fossil fuels from dead remains when decayed
• what are greenhouse gases

  gases in the earths atmosphere that main temperatures on earth high enough to support life

  • examples are CH4 + water vapour + CO2
• what is the greenhouse effect

  • electromagnetic radiation at most wavelengths from the sun passes through earths atmosphere
  • earth absorbs some radiation + warms up earth as needed for human life
  • some heat is radiated from the earth as infrared radiation
  • some of this infrared radiation is absorbed by greenhouse gases in the atmosphere
  • the atmosphere warms up leading to global warming
• what are human activities that contribute to an increase in greenhouse gases in the atmosphere

  activities that increases levels of CO2 + CH4

  
  

  CO2 releases from

  • driving
  • consuming electricity

  CH4 releases from

  • raising livestock like cows
  • decay of organic waste in landfill sites
• how do scientists predict human activity will effect the temperature of earths atmosphere

  increases surface temperature of earths atmosphere

  • this will lead to global climate change
  • it is difficult to mode such a complex system
  • this results in simplified models + speculation that is based on only parts of biased evidence
• what are the potential effects of global climate change

  • extinction of species
  • raising sea levels as polar ice caps melt
  • migration away from areas of drought / flooding
  • decrease in crop yield for all major world crops
• what is a carbon footprint


  the total amount of CO2 + other greenhouse gases emitted over the full life cycle of a product / service / event
• how can you reduce a carbon footprint

  reducing emissions of CO2 + CH4

  • using less electricity -> use alternative energy sources
  • reducing travel times -> of goods or people
  • planting more trees
• why can it be difficult to reduce carbon footprints

  • its more difficult
  • its more expensive
  • planting trees used land that could be used to grow crops
• why is the combustion of fuels enhancing global warming

  it is a major source of atmospheric pollutants
• what happens in the combustion of hydrocarbons

  energy is released

  • carbon + hydrogen in fuels are oxidised to form CO2 + H2O
• what are the properties of carbon monoxide

  • it is a toxic gas
  • colourless + odourless so it is not easy to detect
• what are the properties of sulfur dioxide + nitrogen oxides

  • cause acid rain
  • cause respiratory problems in human
• what are the properties of particulates

  • causes global dimming
  • causes human health problems