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The Atmosphere as a Chemical Reactor

The Atmosphere as a Chemical Reactor. Radiation (energy). Inputs. Outputs. Chemistry. Biogeochemical Cycling. Temperature Structure of the Atmosphere. from: http://www.uwsp.edu/geo/faculty/ritter/images/atmosphere/structure_ composition/atmospheric_structure.jpg.

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The Atmosphere as a Chemical Reactor

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  1. The Atmosphere as aChemical Reactor Radiation (energy) Inputs Outputs Chemistry Biogeochemical Cycling

  2. Temperature Structure of the Atmosphere from: http://www.uwsp.edu/geo/faculty/ritter/images/atmosphere/structure_ composition/atmospheric_structure.jpg

  3. Pressure Structure of the Atmosphere from: http://okfirst.ocs.ou.edu/train/meteorology/graphics/VertTP.gif

  4. Mixing Ratio vs. Concentration • Mixing Ratio – the fraction of air by volume that is composed of a certain compound. • The fraction of N2 is 0.80 or 80% • The fraction of N2O is 3.6x10-7 or 3.6x10-5% or 360 ppbv. • Concentration (number density) – number of molecules of a specified compound contained in a fixed volume. • [N2O] at 1010 mbar = 8.86x1012 molecules/cm3 • [N2O] at 500 mbar = 4.38x1012 molecules/cm3 The atmosphere has a density of 2.69x1019 molecules/cm3at sea level

  5. Chemical Composition of the Atmosphere H2O

  6. Vertical Mixing of the Troposphere • Boundary Layer – hours to days • Free Troposphere – days to weeks • Tropopause - years

  7. Horizontal Mixing of the Troposphere from: Jacob

  8. Horizontal Mixing of the Troposphere

  9. Kinetics

  10. Kinetics Only true for elementary reactions!

  11. Lifetime, Pseudo First Order • First order reaction: • Second order reaction:

  12. Lifetime • Some compounds have multiple sinks • Methane chemical loss in troposphere by OH ≈ 12yrs physical deposition to the soil ≈ 100 yrs chemical loss in stratosphere ≈ 40 yrs Overall lifetime:

  13. Rate Constants

  14. J Values • Photochemistry

  15. Radical Chemistry • Radicals do the work of the chemistry in the atmosphere. • Produced by photochemical reactions and reactions by other radicals • O(3P) is a bi-radical • O(1D) is not a radical, but it is very reactive

  16. The OH Radical

  17. Production of OH Radical Assume steady-state for O(1D) Production Loss

  18. Production of OH Radical Solve for [O(1D)] Substitute into the production of OH

  19. Oxidation of CO

  20. The Chemical Family NOx

  21. The Chemical Family NOx

  22. Coupling of NOx and HOx fast NO slow

  23. Sinks for NOx and HOx

  24. O3 Production

  25. Oxidation of Formaldehyde Maximum O3 production = 3 molecules (high NOx) Maximum HOx production = 2 molecules (high NOx) Minimum O3 production = 0 molecules (low NOx) Minimum HOx producion = -2 molecules (low NOx)

  26. Oxidation of Methane Can oxidize NO to NO2 just like HO2 formaldehyde

  27. O3 Production by Methane • High NOx (maximum O3 and HOx production): • Low NOx (minimum O3and HOx production):

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