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 of molecular 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

9. AIRS CO2
Spatial scales in atm. are a function of residence time and spatial scale of source

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