chemistry of the atmosphere

• air now

  21% oxygen

  78% nitrogen

  1% argon

  0.04% carbon dioxide and water vapour
• early atmosphere- mainly carbon dioxide and no oxygen

  4.6-3.6 b years ago- volcanoes erupt releasing nitrogen and water vapour, water vapour condensed and cools, forming oceans, carbon dioxide dissolved by oceans and locked in fossil fuels and sedimentary rock

  2.7-1.7 b years ago- plants evolve and release oxygen in photosynthesis and take in carbon dioxide
• reduction of CO2 by formation of deposits

  • coal- plants absorb CO2 die and decay, layer compressed to form coal
  • oil and natural gas- plankton absorb CO2, die and deposited in mud on sea floor. covered and compressed over millions of years
  • limestone- shelled animals absorbed CO2 to form their calcium carbonate shells. remains of these animals compressed to form limestone
• carbon monoxide (CO)- pollutant made by incomplete combustion of a hydrocarbon fuel. toxic gas, colourless and odourless so hard to detect.
• sulfur dioxide (SO2)- pollutant- caused by burning coal or petrol which contains sulfur that reacts with oxygen in the air- cause respiratory problems and combine with water vapour to produce acid rain.
• nitrogen oxide (NOx)- caused by car engines, nitrogen and oxygen from air react at high temperatures. cause respiratory problems and combine with water vapour to produce acid rain.
• greenhouse gases- trap heat in earth's atmosphere preventing it escaping into space. main greenhouse gases are water vapour, methane and carbon dioxide. increase in concentration leads to global warming.
• global warming- rise in temperature of earth's surface and lower atmosphere. leading to melting ice caps, rising sea levels, more frequent extreme weather events such as droughts and floods.
• water vapour- most abundant greenhouse gas, formed when liquid water evaporates. traps long wave radiation emitted by earth but not shortwave radiation from sun. increases temperature of earth
• particulates (C) - pollutant- caused by incomplete combustion of a hydrocarbon fuel- leads to global dimming