Atmospheric composition, evolution and vertical structure

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Chapter 1

• Atmospheric composition, evolution and vertical
  structure

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• What elements and compounds are in the
  atmosphere?
• How did these constituents get there?
• What variables do we use to describe the weather?

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• Gases, liquids and solids exist
• 1- abundant gases N2 , O2
• 2- trace gases very small amounts but crucial
  for energy transfer and for life
• H2O
• CO2
• O3
• CH4
• N2O, NO2, SO2
• hydrocarbons, chloroflurocarbons

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• 3- aerosols liquids and solids
• examples rain, snow, dust, smoke,
• volcanic ejecta
• The big, counter-intuitive surprise is that the
• most abundant gas, N2 does not affect
• conditions on the planet like several of the
• trace gases

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• How did we end up with these gases?
• Key factors include
• gravitation f(mass of the earth)
• mean speed of a gas f(molecular weight)
• temperature f(distance to the sun, suns T)
• radiation f( suns T)
• rise of life forms

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• Big bang!? initially copious amounts of H
• and He? rapid escape of these ? volcanic
• outgassing provides H2O (85), CO2 , N2,
• and SO2? uv radiation causes
• disassociation of H2O resulting in O2?
• cooling of atmosphere causes clouds and
• rain ? oceans develop? life forms,
• photosynthesis converts CO2 to O2? CO2
• trapped in sediments? inert N2 and O2
• dominate atmosphere

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• photosynthesis
• 6CO2 6H2O C6H12O6 6O2
• Evidence for the evolutionary scenario
• 1- present day volcanoes yield H2O and CO2
• 2- moon has no atmosphere (weak gravity)
• 3- sun is essentially H and He
• 4- lots of CO2 in sediments

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• The composition of the atmosphere, save for
• one gas, is remarkably steady or very slow
• to change, so how do we describe the
• weather?
• Candidate variables are?
• 1- density mass/volume
• 2- pressure P F/A force acting on an area
• 3- temperature
• 4- winds
• 5- moisture (water vapor does vary)
• 6- pollutants
• 7-visibility

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• Density mass per unit volume
• For air at sea-level, ? 1.2 kg per m3
• 2.65 lbs
  
• for water, ? 1000 kg per m3
• Pressure force per unit area
• weight of the air column above
• lbs per sq. inch, inches of mercury, but
• millibars is easiest
• 1 bar 1000 mb 105 N /m2

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Payne Stewart crash -1999
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• 99 of the air is below 30 km, radius of earth is
  
• 6400 km .atmosphere is 0.5

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Summary CH1

• air is mainly N2 (78) and O2 (21), but
• trace gases (H2O, CO2, O3) play major role
• in the radiation budget (greenhouse gases)
• H2O is the only constituent that changes
• phase naturally, huge amounts of energy
• are absorbed or released as it goes from
• gas to liquid to ice

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• Aerosols solids or liquids in the air, dust
• particles alter radiation and play a major role
• in droplet formation and growth
• ?, P, water vapor all decrease rapidly with
• height but T shows layers the troposphere
• is about 10 km thick, contains all weather,
• stratosphere is stable and radiation driven
• O3 absorbs uv radiation in stratosphere H2O and
• CO2 traps radiation from the earth global
• warming

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