4. Chemistry of the atmosphere

• Proportion of gases in the atmosphere

  • 4/5th (approx 80%) nitogren
  • 1/5th (approx 20%) oxygen
  • Small proportion of various other gases :

  -carbon dioxide

  -water vapour

  -Nobel gases
• the earths early atmosphere


  evidence limited because of the time sale of 4.6 billion years

  • first billion years of earths existence, intense volcanic activity that released gases that formed the early atmosphere
  • water vapour condensed to form oceans
  • start of period earths atmosphere was like Mars + Venus today consisting mainly co2 with little to no o2 gas
  • volcano produced nitrogen which gradually built up in the atmosphere
  • may have been small / portions of methane and ammonia
  • when oceans formed , co2 dissolved in the water and carbonates were predicated producing sediments
  • reduce co2
• how oxygen increased

  • algae and parts produces oxygen by photosynthesis
  • 6 co2 + 6 h2o —> C6H12O6 + 6 o2
  • algae first produced oxygen about 2.7 billion years ago and soon after oxygen appeared in the atmosphere
  • over the next billion years plants evolved and the % if o2 gradually increases it a level that enabled animals to evolve
• how carbon dioxide decreased


  • algae and plants decreased the % of co2 in the atmosphere by photosynthesis
  • CO2 was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon
• formation of:

  • limestone - (sedimentary rocks) mostly made of calcium carbonate deposits from the shells and skeletons of marine organisms
  • coal - thick plant deposits that don’t decompose , covered in sediment and compressed
  • crude oil - deposits of plankton. From reservoirs under the seabed when they get trapped in rock.
  • natural gas - (hydrocarbon methane ) formed from plankton
• Greenhouse gases

  • maintain temperatures on earth high enough to support life

  Eg water Vapor , co2 , methane gas

  • energy from the sun travels to earth as short wave length radiation
  • Some SWLR reflects back off the earth + most passes through
  • Energy of radiation is absorbed by surface of the earth + re radiate LWLR in all directions
  • LWLR (thermal radiation), trapped in atmosphere causing warming of the surface of earth
• Human activities + evidence pros / cons

  • human activities : burning fossil fuels , deforestation , agriculture = increases co2 and methane
  • based on peer reviewed evidence , many scientist believe human activities will cause the temperature of the Earths surface to increase and result in global climate change
  • However difficult to model such complex systems as global climate change
  • Leads to simplified models , speculations presented in the media that may be based on only paths of the evidence which may be biased
• global climate change

  rising temperatures :

  • polar ie caps melting
  • rise in sea levels
  • increased flooding and coastal erosion
  • waster availability
  • affect wild species and leading to changed distribution
• Carbon footprint + reduction

  • total amount of carbon dioxide and other greenhouse gases house gases emitted over the full life cycle of a process , service or event

  Carbon dioxide:

  • renewable energy sourves
  • Carbon capture + storage
  • public transport / walk / cycle
  • Energy efficient appliance

  Methane:

  • eat less beef + diary products
  • Trapping methane and burning to produce electricity
• atmospheric pollutants from fuels

  combustion fuels - major source of atmospheric pollutants

  • coal contain carbon / hydrogen may also contain some sulfur
  • gases released into the atmosphere when a fuel is burned
  • may include co2 , water vapour , carbon monoxide , sulfur dioxide , oxides of nitrogen
  • solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere
• properties and effects of atmospheric pollutants

  • carbon oxide is a toxic gas - it’s colourless and odourless so its not easily detected
  • sulfur dioxide and oxides of nitrogen cause respiratory problems in humans and acid rain
  • particulates causes global dimming and health problems for humans