Atmospheric Chemistry: Topics

1
Atmospheric Chemistry Topics

• Sources, sinks, lifetimes and equilibrium
• Earths chemical cycles, and current trends in
  atmospheric composition
• Review of chemistry
• Reactions rates and equilibria
• Photochemistry
• Aqueous chemistry
• Applications of chemical kinetics to the
  atmosphere
• Troposphere air pollution
• Stratosphere ozone chemistry
• Applications of aqueous chemistry to the
  atmosphere
• pH of precipitation
• Acid rain
• Aerosols in the atmosphere sources and sinks

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Sources, sinks, lifetimes and equilibria
chemical budgets

• See Figure 3-1, Jacob. This applies to any gas
  (or aerosol) in the earths atmosphere. Equation
  3.7.
• Lifetime, or residence time, of a chemical is the
  ratio of the total amount of chemical X to the
  rate of removal of chemical X from the
  atmosphere. (eq 3.1).
• Example. Residence time of water in the
  atmosphere (ex. 3-1)
• Sinks are often proportional to the amount of X
  present. If so, lifetime is independent of the
  amount of X present.
• Example. CFC-12. (ex 3-3)
• With a source and a sink, concentrations approach
  a dynamic equilibrium value. Eq (3.12), Fig 3-2.
• Example. Ozone in the stratosphere.

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Eulerian vs. Lagrangian budgets

• Eulerian budget Stay at one point in space.
  Gases flow in and out undergo chemical
  reactions. Equation 3.7. Suitable, e.g., for
  global budgets or analysis of pollution levels
  over a city.
• Lagrangian budget Follow an air parcel. No
  transport terms (except for turbulent diffusion).
  Equation 3.18. Suitable for tracking, for
  instance, a smokestack plume.

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Two-box model

• Treats transport between two boxes of air, e.g.
• Northern and southern hemispheres
• Troposphere and stratosphere
• Boundary layer and free troposphere
• If the gases within each box are well-mixed
  (equilibrium time gtgt mixing time for the box),
  then we can say the transport from box 1 to box 2
  is proportional to the mass (or density, or
  partial pressure, or mixing ratio) of the gas in
  box 1.