Eats 1011 Lecture 1

Course information

Textbook – 'essentials of meteorology – an invitation to the atmosphere'.

Website - http://horsehead.ccs.yorku.ca/moodle/login/index.php

 

Introduction

 

• Earth's radius – 6370km
  
• Tropical cloud tops ~ 14km
  
• What is our atmosphere made of?
  
  • Permanent gases
    
    • 78.08% nitrogen
      
    • 20.95% oxygen
      
      • If there is too much oxygen things would burst into flames
        
      • If there is too little oxygen then we couldn't breathe properly
        
    • .93% argon
      
    • .0018% neon
      
    • .0005 helium
      
    • .00006 hydrogen
      
    • .000009 xenon
      
  • Mixing ratios by volume =
  • Composition constant to stand up to ~ 90km
  • Permanent gases all have very long lifetimes
  • O₂ is consumed by burning fossil fuels but released by photosynthesis, changes by ~ 20 ppmv in 10 years
  • Ppmv =     Parts per million volume
  • Variable gases
    • 0-4% water vapor
      • Water exists in 3 phases on earth
        • vapour
        • liquid
        • solid
      • most is in the bottom 3km
      • latent heat release is important
      • vapour 'invisible', but absorbs light in near IR and throughout the IR – Greenhouse Gas(GHG)
      • condensed cloud and water droplets
      • frozen air ice pellets, crystals and snow
    • .037% carbon dioxide (375 ppm)
      • Greenhouse gas (GHG) – 370 ppmv
      • Increasing at ~.4% / year
      • 16% from 1958 (figure 1.3 ahrens)
      • 32% from beginning of industrial revolution
      • 'lifetime' ~ 250 years
      • Sources of CO₂
        • reverse photosynthesis
        • O₂ + sugar / food à CO₂ + H₂O
          • Wintertime CO₂ increases
        • decay of vegetation
        • exhalations of animals / people (burning)
        • burning of fossil fuels(coal, oil, natural gas)
        • deforestation (burned or left to rot)
        • volcanic eruptions
      • Sinks
        • removal by photosynthesis
        • CO₂ + H₂O + Visible light à O₂ + sugar
        • ocean sinks
          • CO₂ dissolves in oceans (à 50 times the total atmospheric CO₂)
          • Phytoplankton(tiny plants) fix CO₂ into organic tissues
          • Mixes downward in oceans
          • Summertime CO₂
    • .00017 methane (1.7ppm)
      • CH₄ = Methane
      • GHG – 1.7 ppmv
      • Increasing by .5% per year
      • Lifetime – 10 years
      • Sources
        • termites (biological activity). Anaerobic (no oxygen) breakdown of plant material by bacteria
          • rice paddies
          • wetlands
        • enteric fermentation
          • cows, elephants flatulence
          • landfills
          • pipeline loss
      • Sinks
        • loss by chemical reactions in the atmosphere
    • .00003 nitrous oxide (.3 ppm)
    • .000004 ozone (.04ppm)
      • O₃ - ozone
      • Most of the ozone is in the stratosphere (20-50km)
      • Serves as a UV filter (<300nm)
      • Secondary pollutant
        • mixture of NOx and hydrocarbon gases
        • causes respiratory problems
    • .000001 particles (dust, soot, etc) (.01 - .15ppm)
      • Aerosols
        • Natural sources
          • Volcanoes, forest fires, blown dust, sea salt, trees
        • Anthropogenic sources
          • Roads, biomass burning, emissions, reactions in the atmosphere
        • Health issues, smaller particles are more lethal
          • PM 2.5µm
        • N.B. cloud/rain not normally included as aerosols
    • .00000002 chlorofluorocarbons (CFC's) (.0002ppm)
  • 1.7 ppmv means that for every million air molecules in a volume 1.7 are methane molecules
• Ice cores from Arctic and Antarctic
  • Greenland is about 3000 m
  • Antarctica 3000 m
  • was our atmosphere always like this?
    • Our universe is about 15 billion years old
    • Solar system formed from rotating debris
      • Planets planetsimals asteroids comets
    • Earth formed about 4.5 billion years ago
      • Pulverized by colliding bodies
      • Atmosphere of H₂, He
      • Swept away by early solar wind
    • It is likely that we have a secondary or tertiary atmosphere
    • Likely there was a volcanic outgassing
    • Emissions from current volcanoes
      • 80% water
      • 10% CO₂
      • 2% nitrogen
      • Variable% SO₂
        
    • Cooling
      • water formed oceans
        • not much land
    • collisions
      • formation of moon
      • possible cometary source of water
    • sun
      • 1bya
        • Earth was almost completely frozen
        • Atmosphere
          • Water, CO₂,
            • completely different from today
    • early atmosphere had no capacity for shielding from UV radiation from the sun
      • absorption limits
      • **
    • So where did our O₂ atmosphere come from?
      • Water photolysis generates O₂ and ozone (.3µ)
    • Photosynthesis
      • N(CO₂ + H₂O) + sunlight à (H₂CO)n + nO₂(day)
      • O₂ + H₂CO à CO₂ + H₂O (night) "burning": energy release
      • Death/burial of C à O₂ remains in atmosphere
    • Summary

Most of the carbon is in sedimentary rocks so that the CO₂ – N₂ budget is similar to that of Venus in absolute amounts and to mars in ratio