1. The Atmosphere as a Chemical Reactor OutputsInputs Chemistry Radiation (energy) 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 N 2 is 0.80 or 80% –The fraction of N 2 O 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. –[N 2 O] at 1010 mbar = 8.86x10 12 molecules/cm 3 –[N 2 O] at 500 mbar = 4.38x10 12 molecules/cm 3 The atmosphere has a density of 2.69x10 19 molecules/cm 3 at sea level

5. Chemical Composition of the Atmosphere CompoundMixing Ratio N2N2 0.78 O2O2 0.21 Ar0.0093 CO 2 3.6x10 -4 Ne8x10 -6 He5.2x10 -6 CH 4 1.7x10 -6 Kr1.1x10 -6 H2H2 5.0x10 -7 N2ON2O3.6x10 -7 Xe9.0x10 -8 O3O3 1 – 10x10 -8 H2OH2O

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. 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( 3 P) is a bi-radical O( 1 D) is not a radical, but it is very reactive

16. The OH Radical

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

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

19. Oxidation of CO

20. The Chemical Family NO x

22. Coupling of NO x and HO x NO slow fast

23. Sinks for NO x and HO x

24. O 3 Production

25. Oxidation of Formaldehyde Maximum O 3 production = 3 molecules (high NO x ) Maximum HO x production = 2 molecules (high NO x ) Minimum O 3 production = 0 molecules (low NO x ) Minimum HO x producion = -2 molecules (low NO x )

26. Oxidation of Methane Can oxidize NO to NO 2 just like HO 2 formaldehyde

27. O 3 Production by Methane High NO x (maximum O 3 and HO x production): Low NO x (minimum O 3 and HO x production):