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Atmospheric Chemistry. Texts: W+H, Chap 5 S+P, selected readings from Chaps. 1-7 Divided into Two Parts Gas Chemistry Aerosol Chemistry – Next semester Relevance Pollution/Air Quality/Acid Rain Climate Ozone layer. Atmospheric Composition Revisited. Atmospheric Composition Revisited.

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atmospheric chemistry
Atmospheric Chemistry
  • Texts:
    • W+H, Chap 5
    • S+P, selected readings from Chaps. 1-7
  • Divided into Two Parts
    • Gas Chemistry
    • Aerosol Chemistry – Next semester
  • Relevance
    • Pollution/Air Quality/Acid Rain
    • Climate
    • Ozone layer
units
Units
  • Normally, units of mixing ratio used, xi
    • Mole fraction = Volume Fraction
      • ppm = 10-6
      • ppb = 10-9
      • ppt = 10-12
      • “ppx” = “ppxv”
    • Mass fraction is different – also called mixing ratio – beware
    • Must multiply volumetric mixing ratio by the ratio of molecular weights to get mass fraction.
review of conversions
Review of Conversions
  • Mixing Ratio (volumetric), xi
  • Mixing Ratio (by mass), ri
  • Partial Pressure, pi
  • Molar concentration (moles/m3), ci
  • Mass concentration (mg/m3), ri
  • Molecular concentration (#/m3), ni
mixing ratio vs molar concentration
Mixing Ratio vs. Molar Concentration
  • n is a strong function of p (i.e. z)
  • Consider vertical profiles in each quantity
lifetimes and spatial scales of molecular species
Lifetimes and spatial scales ofmolecular species

t = Q/R

Q = abundance

R = removal rate

P = production rate

t = mean lifetime

dQ/dt = P – R

Assumes a closed system

Very often,

R  krQ

tropospheric o 3
Tropospheric O3

http://aura.gsfc.nasa.gov/science/top10_omi-mls-maps.html

airs co 2
AIRS CO2

Spatial scales in atm. are a function of residence time and spatial scale of source

http://www-airs.jpl.nasa.gov/images/AIRS_CO2_July2003_550x396.jpg

the key elemental players
The key elemental players
  • Oxygen and Hydrogen
    • O 6 valence electrons – highly electronegative
    • O2 accumulation the result of photosynthesis
    • H2O main reservoir for H
    • Key reactive species are O3 O, OH, HO2, all produced by photochemistry
    • Result in an oxidizing atmospheric environment
the key elemental players1
The key elemental players
  • Nitrogen
    • N – 5 valence electrons
    • N2 VERY stable in atmosphere
    • Rest of species called “fixed nitrogen”, having oxidation states from +3 to -5
    • Key sources of reactive nitrogen are bacteria lightning, and fertilizer production
    • Key atmospheric players are N2O, NO, NO2, and NH3.
    • Also present in many organic species
the key elemental players2
The key elemental players
  • Carbon
    • C – 4 valence electrons
    • CO2 is the key atmospheric reservoir
    • Other players are CO (a pollutant) CH4 (a greenhouse gas), and the countless organic species
    • Cycles involve the land surface, biosphere, oceans, and anthropogenic processes
    • Much of the atmospheric aerosol is of organic composition
the key elemental players3
The key elemental players
  • Sulfur
    • S – 6 valence electrons; a chalcogen like O
    • SO2 and DMS are the key sources
    • Strongly influenced by fossil fuel emissions, esp. coal burning
    • Some dry deposition – mostly converted to sulfate aerosol (SO42-) – source of east-coast smog
    • Much of the atmospheric aerosol is sulfate
sources
Sources
  • Biogenic
  • Terrestrial
  • Anthropogenic
  • Oceanic
sinks
Sinks
  • Deposition
    • Dry deposition
    • Wet deposition
  • In situ reactions
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