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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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