1. QUESTIONS
Atmospheric CO2 has a lifetime (turnover time) of 5 years against photosynthesis and a lifetime of 10 years against dissolution in the oceans. What is its overall atmospheric lifetime?
2. Are the following loss processes first-order (linear with concentration?    A. Uptake of CO2 by the biosphere    B. Photolysis of gases in the stratosphere
   C. Scavenging of aerosol particles by precipitation
3. The Montreal protocol banned worldwide production of CFC-12 as of CFC-12 is removed from the atmosphere by photolysis in the stratosphere and the resulting CFC-12 atmospheric lifetime is 100 years. Assuming full compliance with the Montreal protocol, how long will it take for CFC-12 concentrations to drop to half of present-day values?
4. Consider a 2-box model for the atmosphere where one box is the troposphere ( hPa) and the other the stratosphere
(150-1 hPa).  The lifetime of air in the stratosphere is 2 years.  What is the lifetime of air in the troposphere?
5. . Of the simple models we discussed in chapter 3, which one would be best suited for addressing the following problems?  
a. Is the observed rise of atmospheric CO2 concentrations consistent with the known rate of CO2 emission from fossil fuel combustion? 
b. Large amounts of radioactive particles are released to the atmosphere in a nuclear power plant accident. Which areas will be affected by this radioactive plume? 
c. An air pollution monitoring station in Fort Collins suddenly detects high concentrations of a toxic gas. Where is this gas coming from?

2. CHAPTER 6: GEOCHEMICAL CYCLES
THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTS
Most abundant elements: oxygen (in solid earth!), iron (core), silicon (mantle), hydrogen (oceans), nitrogen, carbon, sulfur…
The elemental composition of the Earth has remained essentially unchanged over its 4.5 Gyr history
Extraterrestrial inputs (e.g., from meteorites, cometary material) have been relatively unimportant
Escape to space has been restricted by gravity
Biogeochemical cycling of these elements between the different reservoirs of the Earth system determines the composition of the Earth’s atmosphere and oceans, and the evolution of life

3. BIOGEOCHEMICAL CYCLING OF ELEMENTS: examples of major processes
Physical exchange, redox chemistry, biochemistry are involved
Surface
reservoirs

4. HISTORY OF EARTH’S ATMOSPHEREN2
CO2
H2O O2
O2 reaches current levels; life invades continents
oceans form
CO2
dissolves
Life forms in oceans
Onset of
photosynthesis
Outgassing
4.5 Gy
B.P
4 Gy
B.P.
3.5 Gy
B.P.
0.4 Gy
B.P.
present

5. COMPARING THE ATMOSPHERES OF EARTH, VENUS, AND MARS
Radius (km)
6100
6400
3400
Surface pressure (atm) 91 1
0.007
CO2 (mol/mol)
0.96
3x10-4
0.95
N2 (mol/mol)
3.4x10-2
0.78
2.7x10-2
O2 (mol/mol)
6.9x10-5
0.21
1.3x10-3
H2O (atm, mol/mol)
3x10-3
1x10-2

6. EVOLUTION OF O2 AND O3 IN EARTH’S ATMOSPHERE

7. Atmospheric Composition (average) 1 ppm= 1x10-6 red = increased by human activity
Gas
Mole fraction
Nitrogen (N2)
0.78
Oxygen (O2)
0.21
Water (H2O)
0.04 to < 5x10-3; 4x10-6 -strat
Argon (Ar)
0.0093
Carbon Dioxide (CO2)
370x10-6 (date: 2000)
Neon (Ne)
18.2x10-6
Ozone (O3) ¶
0.02x10-6 to 10x10 –6
Helium (He)
5.2x10-6
Methane (CH4)
1.7x10-6
Krypton (Kr)
1.1x10-6
Hydrogen (H2)
0.55x10-6
Nitrous Oxide (N2O)
0.32x10-6
Carbon Monoxide (CO)
0.03x10-6 to 0.3x10-6
Chlorofluorocarbons
3.0x10-9
Carbonyl Sulfide (COS)
0.1x10-9
¶ Ozone has increased in the troposphere, but decreased in the stratosphere.

8. NOAA Greenhouse Gas records
Montreal Protocol- 1996

9. Nitrogen:
Nitrogen is a major component of the atmosphere, but an essential nutrient in short supply to living organisms. Why is "fixed" nitrogen in short supply? Why does it stay in the atmosphere at all?
OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell a9 oxidation states from –3 to +5
Increasing oxidation number (oxidation reactions)
Fixed N = odd N -3 +1 +2 +3 +4 +5
NH3
Ammonia
NH4+
Ammonium
R1N(R2)R3
Organic N N2
N2O
Nitrous
oxide NO
Nitric oxide
HONO
Nitrous acid
NO2-
Nitrite
NO2
Nitrogen dioxide
HNO3
Nitric acid
NO3-
Nitrate
N2O5
Nitrogen pentoxide
free radical
free radical
Decreasing oxidation number (reduction reactions)

10. THE NITROGEN CYCLE: MAJOR PROCESSES
combustion
lightning
free radical
ATMOSPHERE N2 NO
oxidation
HNO3
denitri-
fication
biofixation
deposition
orgN
decay
NH3/NH4+
NO3-
BIOSPHERE
assimilation
nitrification
weathering
burial
LITHOSPHERE
"fixed" or "odd" N is less stable globally than N2

11. BOX MODEL OF THE NITROGEN CYCLE
Inventories in Tg N
Flows in Tg N yr-1

12. N2O: LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION AND DENITRIFICATION
Important as
source of NOx radicals in stratosphere
greenhouse gas
IPCC
[2001]

13. N2O versus depth in the Greenland Ice sheet.
Constraints on N2O budget changes since pre-industrial time from new firn air and ice core isotope measurements
S. Bernard, T. R¨ockmann, J. Kaiser, J.-M. Barnola, H. Fischer, T. Blunier, and J. Chappellaz, Atmos. Chem. Phys., 6, 493–503, 2006
N2O in the atmosphere

14. PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N2O
SOURCES (Tg N yr-1)
18 (7 – 37)
Natural
10 (5 – 16)
Ocean
3 (1 - 5)
Tropical soils
4 (3 – 6)
Temperate soils
2 (1 – 4)
Anthropogenic
8 (2 – 21)
Agricultural soils
4 (1 – 15)
Livestock
2 (1 – 3)
Industrial
1 (1 – 2)
SINK (Tg N yr-1)
Photolysis and oxidation in stratosphere
12 (9 – 16)
ACCUMULATION (Tg N yr-1)
4 (3 – 5)
IPCC
[2001]
Although a closed budget can be constructed, uncertainties in sources are large!
(N2O atm mass = kg x x28/29 = 1535 Tg )

15. BOX MODEL OF THE N2O CYCLE
Inventories in Tg N
Flows in Tg N yr-1 3 6 8
N2O

18. SULFUR CYCLE
Most sulfur is tied up in sediments and soils. There are large fluxes to the atmosphere, but with short atmospheric lifetimes, the atmospheric S burden is small.
SO2: Anthropogenic (fossil fuel combustion) source comparable to natural sources (soils, sediments, volcanoes)
Sulfur is oxidized in the atmosphere: SO > H2SO4
S(+IV) S(+VI)
Sulfate is an important contributor to
acidity of precipitation. Sulfuric acid has
a low Pvap and thus partitions primarily
to aerosol/aqueous phase
Strongly perturbed by human activities!

19. FAST OXYGEN CYCLE: ATMOSPHERE-BIOSPHERE
Source of O2: photosynthesis
nCO2 + nH2O g (CH2O)n + nO2
Sink: respiration/decay
(CH2O)n + nO2 g nCO2 + nH2O
CO2
O2 lifetime: 5000 years
Photosynthesis
less respiration O2
orgC
orgC
decay
litter

20. …however, abundance of organic carbon in biosphere/soil/ocean reservoirs is too small to control atmospheric O2 levels

21. SLOW OXYGEN CYCLE: ATMOSPHERE-LITHOSPHERE
O2 lifetime: 3 million years
O2: 1.2x106 Pg O
CO2 O2
Photosynthesis
decay
Fe2O3
H2SO4
runoff
weathering
CO2 O2
FeS2
orgC
OCEAN
CONTINENT
orgC
Uplift
burial
CO2
orgC: 1x107 Pg C
FeS2: 5x106 Pg S
microbes
orgC
FeS2
SEDIMENTS
Compression
subduction

22. ATMOSPHERIC CARBON
Unreactive Carbon: CO2: GHG (more to follow…) (tATM~20 yrs)
Reactive Carbon: CH4: GHG, important in oxidant chemistry (tATM~9 yrs)
CO: important in oxidant chemistry (later…) (tATM~2 mos)
NMHCs: source of CO, oxidant chemistry (tATM~sec-mos)
Black Carbon: radiatively important (tATM~days)
CH4 (C= -IV)
CO (C= +II)
CO2 (C= +IV)
Oxidation

23. ATMOSPHERIC METHANE (CH4)
Important: as a GHG and as it affects the oxidizing capacity of troposphere

24. SOURCES OF ATMOSPHERIC METHANE
BIOMASS
BURNING 20
ANIMALS 90
WETLANDS
180
LANDFILLS 50
GLOBAL METHANE
SOURCES (Tg CH4 yr-1)
GAS 60
TERMITES 25
COAL 40
RICE 85

25. SINKS OF ATMOSPHERIC METHANE
Transport to the Stratosphere
Only a few percent, rapidly destroyed  BUT the most important source of water vapour in the dry stratosphere
II. Oxidation
CH4 + OH  CH3O2CO + other products O2
Lifetime ~ 9 years

26. IPCC [2001] Projections of Future CH4 Emissions (Tg CH4) to 2050
ATMOSPHERIC CH4: PAST TRENDS, FUTURE PREDICTIONS
IPCC [2001] Projections of Future CH4 Emissions (Tg CH4) to 2050
Variations of CH4 Concentration (ppbv)
Over the Past 1000 years
[Etheridge et al., 1998]
Scenarios
900
A1B
A1T
A1F1 A2 B1 B2
IS92a
1600
1400
800
1200
700
1000
800
600
1000
1500
2000
2000
2020
2040
Year
Year

27. Pinatubo
Fires
Low T / precip