1. ATS 621 Fall 2012
Lecture 6

2. Tropospheric ozone cycle
The average lifetime of O3 in the troposphere has been estimated at 22 (±2) days (Stevenson et al. 2006); however, it varies with altitude and ranges from 1–2 days in the boundary layer where dry deposition is the major sink, to several weeks in the upper troposphere.
This, in combination with the potential for O3 to be produced from precursors long after they have been emitted, makes O3 a global (hemispheric) pollutant.
4100 Tg yr-1
Notice the link to N
“Ground-level ozone in the 21st century: future trends, impacts and policy implications”; report by The Royal Society, 2008

3. Surface concentrations of ozone
US Standard:
8 hour avg < 75 ppb

4. Trends?
At very low concentrations of NOX (<20 ppt) O3 is destroyed, and this is the main cause of the very low O3 concentrations over remote oceans
In contrast to these remote areas, over the polluted continents, in Europe, North America and large parts of East and South Asia, Africa and South America, there is sufficient NOX to produce O3 .
The hemispheric background O3 concentration in many areas is thought to have roughly doubled between 1900 and 1980 and has risen further since
Rural O3 concentrations have increased in many areas at different rates. In Northern Hemisphere mid-latitudes, where the majority of global population and food production occurs, the increase in background O3 since 1980 was of the order of 5 ppb.
The cause of the increase appears mainly to be an increase in net chemical production in the troposphere, although increases in the stratospheric source of O3 may also have contributed.
“Ground-level ozone in the 21st century: future trends, impacts and policy implications”; report by The Royal Society, 2008

5. Increasing ozone at high mountain sites in the Alps
…..attributed in part to increased stratospheric-tropospheric exchange

7. OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell a9 oxidation states from –3 to +5
Increasing oxidation number (oxidation reactions) -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)
This slide and many of next ones are courtesy Prof. Colette Heald

8. THE NITROGEN CYCLE: MAJOR PROCESSES
ATMOSPHERE
combustion
lightning
free radical
Denitrification is the microorganism- mediated process which reduced fixed N (nitrate), generally into an inert form, N2 or N2O.
Nitrogen fixation is any process in which N2 in the atmosphere reacts to form any N compound. 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=> N2

9. Notice only N2O is shown as being transported to the stratosphere (long lifetime….)
Anthropogenic contributions to fixation occur in production of ammonia fertillizers and in combustion processes which form NOx from N2.
Haber-Bosch process: Under high temperatures and very high pressures, hydrogen and nitrogen (from air) are combined to produce ammonia.
“Fritz Haber and Carl Bosch have probably had a greater impact than anyone in the past 100 years. Their Haber-Bosch process has often been called the most important invention of the 20th century (e.g., V. Smil, Nature, July , p 415) as it "detonated the population explosion," driving the world's population from 1.6 billion in 1900 to 6 billion in 2000.” –

11. “odd nitrogen”: everything except N2 and N2O
Implicated in long-range transport of NOx
Nitrogen reservoirs, including particles
“odd nitrogen”: everything except N2 and N2O

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

13. N2O: LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION AND DENITRIFICATION
Important as
source of NOx radicals in stratosphere
greenhouse gas
IPCC
[2007]

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!

15. BOX MODEL OF THE N2O CYCLE
Inventories in Tg N
Flows in Tg N yr-1 3 6 8
N2O 12

16. OXIDATION STATES OF SULFUR S has 6 electrons in valence shell a oxidation states from –2 to +6
Increasing oxidation number (oxidation reactions) -2 +4 +6
FeS2
Pyrite
H2S
Hydrogen sulfide
(CH3)2S
Dimethylsulfide (DMS)
CS2
Carbon disulfide
COS
Carbonyl sulfide
SO2
Sulfur dioxide
H2SO4
Sulfuric acid
SO42-
Sulfate
Decreasing oxidation number (reduction reactions)

17. THE GLOBAL SULFUR CYCLE
(sources in Tg S y-1)
SO42-
SO2
H2S
ATMOSPHERE
2.8x1012 g S
t = 1 week
SO2
CS2
COS
(CH3)2S 10
deposition 60
runoff 20
plankton
OCEAN
1.3x1021 g S
t = 107 years
coal combustion
oil refining
smelters
volcanoes
SO42-
microbes
vents
uplift
SEDIMENTS
7x1021 g S
t = 108 years
FeS2

18. Global sulfur cycle

19. New interest in OCS “Corralling the carbon cycle”
Published: Thursday, November 13, :23 in Earth & Climate
Scientists may have overcome a major hurdle to calculating how much carbon dioxide (CO2) is absorbed and released by plants, vital information for understanding how the biosphere responds to stress and for determining the amount of carbon that can be safely emitted by human activities. The problem is that ecosystems simultaneously take up and release CO2. The key finding is that the compound carbonyl sulfide, which plants consume in tandem with CO2, can be used to quantify gas flow into the plants during photosynthesis. The research is published in the November 14, issue of Science. "In photosynthesis, plants 'breath' in carbon dioxide from the atmosphere and, with sunlight energy, convert it and water into food and oxygen, which they then 'exhale,'" explained co-author Joe Berry from the Carnegie Institution's Department of Global Ecology. "In ecosystems, plants and other organisms respire producing carbon dioxide. We can measure the net change in CO2, but we do not have an accurate way to measure how much is going in or out and how this is affected by climate. Understanding this photosynthesis-climate feedback riddle is key to understanding how climate change may affect the natural processes that are a sink for human-made carbon emissions."
Previous laboratory research showed that carbonyl sulfide is taken up in step with photosynthesis. But unlike CO2, there is no emission of carbonyl sulfide from plants.

20. Source Regions for DMS
Lana, A., et al. (2011), An updated climatology of surface dimethlysulfide concentrations and emission fluxes in the global ocean, Global Biogeochem. Cycles, 25, GB1004, doi: /2010GB

21. Ocean currents (sources of upwelling)

22. Winds blowing across the ocean surface often push water away from an area. When this occurs, water rises up from beneath the surface to replace the diverging surface water. This process is known as “upwelling.” Subsurface water that rises to the surface as a result of upwelling is typically colder, rich in nutrients, and biologically productive. Therefore, good fishing grounds typically are found where upwelling is common. For example, the rich fishing grounds along the west coasts of Africa and South America are supported by year-round coastal upwelling.
Seasonal upwelling and downwelling also occur along the West Coast of the United States. In winter, winds blow from the south to the north, resulting in downwelling. During the summer, winds blow from the north to the south, and water moves offshore, resulting in upwelling along the coast.  This summer upwelling produces cold coastal waters in the San Francisco area, contributing to the frequent summer fogs. (Duxbury, et al, 2002.)

23. The CLAW Hypothesis
Charlson, R. J., Lovelock, J. E., Andreae, M. O. and Warren, S. G. (1987). "Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate". Nature 326 (6114): 655–661.

24. Halogens (F, Cl, Br, I)

25. Ozone depletion in BL in Arctic
Ozone and BrO concentrations during a low ozone event in spring 1996 in Ny Ålesund, Spitsbergen [Tuckermann et al. 1997]. From

26. Carbon cycle
Isoprene, mono-terpenes