The First Lecture of ATS 113 by Ejx7jD8z

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									The First Lecture
  of ATS 113
  Jon M. Schrage
   Overview of the Atmosphere:




• The atmosphere is very thin:

     Earth : apple :: atmosphere : apple’s skin
     Overview of the Atmosphere:


Actually, there is no “top”
to the atmosphere…
     Overview of the Atmosphere:


Actually, there is no “top”
to the atmosphere…

• 90% is below 16 km (10 miles)
• 99% is below 50 km (30 miles)
• 99.999997% is below 100 km (60 miles)
            “Air”
A mixture of gases and aerosols
            “Air”
A mixture of gases and aerosols
            Each gas has:
• sources – processes that add (“input”) the
  gas into the atmosphere



• sinks – processes that remove (“output”)
  the gas from the atmosphere
             Each gas has:
• sources – processes that add (“input”) the
  gas into the atmosphere
  – For water vapor, this would be
    EVAPORATION.
• sinks – processes that remove (“output”)
  the gas from the atmosphere
  – For water vapor, this would be
    CONDENSATION.
           Each gas has a:
• reservoir – the amount of the gas currently
  being held in to the atmosphere

• residence time – how long a typical
  molecule of the gas is going to be in the
  atmosphere before being removed by a
  sink
                        reservoir
      residence time 
                       input rate
                        reservoir
      residence time 
                       input rate
• Consider the case of water vapor:
  – The “reservoir” of water vapor is relatively
    small (compared to other gases).
  – However, the input rate is very, very fast—
    there is lots of evaporation.
  – Therefore, the residence time is pretty short—
    about 10 days.
                        reservoir
      residence time 
                       input rate
• Consider the case of oxygen:
  – The “reservoir” of water vapor is relatively
    large (compared to other gases).
  – The input rate is fairly fast (photosynthesis in
    plants).
  – Therefore, the residence time is pretty
    moderate—about 500 years.
                        reservoir
      residence time 
                       input rate
• Consider the case of nitrogen:
  – The “reservoir” of nitrogen is huge (compared
    to other gases).
  – However, the input rate is very, very slow—
    there is almost no production of N2.
  – Therefore, the residence time is very long—
    about 42 million years.
“Residence time” is important…
…because it helps explain the difference
  between two types of gases in the
  atmosphere:
                                     Occur in about the same
                                     concentration at every
                                     location in the atmosphere.
1. Constant (“permanent”) constituents
2. Variable constituents

                  Occur at a range of concentrations at
                  different locations in the atmosphere.
       Constant (“Permanent”)
           Constituents
• Their concentration is in “steady state”.
• Their sources and sinks are in some kind
  of “equilibrium”.
        Constant (“Permanent”)
            Constituents
•   Nitrogen 78%
•   Oxygen 21%
•   Argon .9%
•   Neon .0018%




                       Nitrogen   Oxygen   Argon   Neon
         Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
•   Ozone (averages about 0.01%)
•   Methane (average about 0.00017%)
Variability of Water Vapor
         Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
•   Ozone (averages about 0.01%)
•   Methane (average about 0.00017%)
   Variability of Carbon Dioxide




• Trend (due to the burning of fossil fuels)
• Annual Cycle (due to the fact that there are more
  plants in the Northern Hemisphere than the
  Southern Hemisphere)
         Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
•   Ozone (averages about 0.01%)
•   Methane (average about 0.00017%)
Variability of Ozone
         Variable Constituents
•   Water Vapor 0-4% (averages about 0.25%)
•   Carbon Dioxide (averages about 0.038%)
•   Ozone (averages about 0.01%)
•   Methane (average about 0.00017%)
        Variability of Methane




• Sources of methane: cattle flatulence, termites,
  rice paddies…
Aerosols
               Aerosols
• The atmosphere also contains
  “aerosols”— suspended solid and liquid
  particles (other than water and ice).
• Soot, smoke, dust, salt, pollen…
Origin of the
Atmosphere
   First
Atmosphere:
Formed about 4
billion years ago.
Mostly hydrogen
 and helium.
  We lost this
  atmosphere.
  Second
Atmosphere:
Formed by volcanic
   outgassing.
 Nitrogen, carbon
  dioxide, water
      vapor…
Oxygen
                Oxygen



• Does not occur due to volcanic
  outgassing.
• Byproduct of photosynthesis.
• Concentrations rose (from zero) once life
  evolved.

								
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