The Atmosphere

The Atmosphere

1. Composition

   • Gases
     • Nitrogen - 78%
       • used in proteins
     • Oxygen - 21%
       • Used in aerobic repiration
     • Carbon Dioxide - 0.04%
       • Used in photosynthesis
     • Methane - 0.00017%
       • Source of Carbon for chemoautotrophs
     • Ozone - 0.000007%
       • Absorbs UV radiation in the stratosphere
     • Water Vapour - up to 4%
       • Water in the water cycle is distributed in the atmosphere
   • Changes with time
     • [CO2] in the atmosphere rises at night and drops in the day
       • Rises at night - respiration occurs but photosynthesis doesn't Drops in the day - Photosynthesis is much quicker than respiration so more CO2 is used up
       • Fluctuations are greater in Summer than in Winter
         • higher light levels and temperatures make both processes much more rapid
     • [H2O] in the atmosphere varies, vegetation releases water vapour by transpiration
       • Evaporation and precipitation rates are effected by temperature
         • Water vapour variations are greatest near the ground
   • Changes with altitude
     • More ozone naturally occurs in the Stratosphere where UV interacts with O2
     • In the troposphere temperature decreases with increasing altitude due to heating from IR radiation from the ground (re-radiated)
       • In the stratosphere temperature increases with increasing altitude due to heating from UV radiation from the Sun
         • These changes in temperature, pressure and energy produce a sequence of layers in the atmosphere
           • 1) Toposphere
           • 3) Mesosphere
           • 2) Stratosphere
           • 4) Thermosphere
   • Solar radiation
     • Nuclear fusion in the sun releases lots of energy as electromagnetic radiation
     • The electromagnetic radiation that reaches the Earths atmosphere includes: visible light, infrared and ultraviolet radiation
       • Some of this radiation is absorbed by the atmosphere, especially UV being absorbed by ozone
         • Water vapour and CO2 also absorb some wavelengths of radiation

2. Human Impacts

   • The composition of the atmosphere is being changed by humans many processes in the atmosphere are interconnected
   • Climate Change
     • The Greenhouse Effect
       • Natural process that controls heat + energy balance of earths surface and the atmosphere
         • Visible light passes through atmosphere easily and is absorbed by the earth, it is then converted to heat energy and emitted as IR radiation
           • This IR radiation is partly absorbed by gases in the atmosphere, causing the atmosphere to become warmer until it is re-radiated into space
       • The enhanced greenhouse effect is the increase of gases that absorb IR radiation because of human activity
     • Consequences of Climate Change
     • Predicting Climate Change
     • Feedback Mechanisms
     • Strategies to Control Climate Change
   • Ozone Depletion
     • UV light absorption