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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. Atmospheric Composition Revisited. Atmospheric Composition Revisited.

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Atmospheric Chemistry

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  1. 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

  2. Atmospheric Composition Revisited

  3. Atmospheric Composition Revisited

  4. 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.

  5. 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

  6. Mixing Ratio vs. Molar Concentration • n is a strong function of p (i.e. z) • Consider vertical profiles in each quantity

  7. 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

  8. Tropospheric O3 http://aura.gsfc.nasa.gov/science/top10_omi-mls-maps.html

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. Sources • Biogenic • Terrestrial • Anthropogenic • Oceanic

  15. Sinks • Deposition • Dry deposition • Wet deposition • In situ reactions

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