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QUESTIONS

QUESTIONS. 1. Is the general atmospheric circulation stronger (i.e., are the winds faster) in the winter or in the summer hemisphere?

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QUESTIONS

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  1. QUESTIONS 1. Is the general atmospheric circulation stronger (i.e., are the winds faster) in the winter or in the summer hemisphere? 2. Concentrations of CO2, krypton-85, and other gases emitted mainly inthe northern hemisphere DECREASE with altitude in the northernhemisphere but INCREASE with altitude in the southern hemisphere.Explain. 3. Kuwaiti oil fires during the Persian Gulf war produced large clouds of soot a few km above the Earth's surface. Soot absorbs solar radiation. How would such soot clouds affect atmospheric stability? 4. Where in the world would you expect the atmosphere to be most unstable? 5. Consider a pollutant emitted from the surface at a constant rate. Is its surface air concentration higher in the day or at night? In summer or winter?

  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 cyclingof 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 ATMOSPHERE N2 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. 0.4 Gy B.P. 3.5 Gy B.P. present

  5. COMPARING THE ATMOSPHERES OF EARTH, VENUS, AND MARS

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

  7. Atmospheric Composition (average)1 ppm= 1x10-6red = increased by human activity ¶ Ozone has increased in the troposphere, but decreased in the stratosphere.

  8. NOAA GREENHOUSE GAS RECORD

  9. OXIDATION STATES OF NITROGENN has 5 electrons in valence shell a9 oxidation states from –3 to +5 Increasing oxidation number (oxidation reactions) 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=> 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 [2007]

  13. PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N2O IPCC [2001] Although a closed budget can be constructed, uncertainties in sources are large! (N2O atm mass = 5.13 1018 kg x 3.25 10-7 x28/29 = 1575 Tg )

  14. 1.57 103 N2O 6 8 3 Inventories in Tg N Flows in Tg N yr-1 BOX MODEL OF THE N2O CYCLE 12

  15. OXIDATION STATES OF SULFURS has 6 electrons in valence shell a oxidation states from –2 to +6 Increasing oxidation number (oxidation reactions) Decreasing oxidation number (reduction reactions)

  16. 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

  17. 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

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

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

  20. 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

  21. 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

  22. 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

  23. 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 1500 1000 2000 2020 2040 2000 Year Year

  24. Recent slow-down in growth rate Pinatubo Fires Tropical wetlands Low T / precip

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