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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
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?

chapter 6 geochemical cycles
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
biogeochemical cycling of elements examples of major processes
BIOGEOCHEMICAL CYCLING OF ELEMENTS:examples of major processes

Physical exchange, redox chemistry, biochemistry are involved

Surface

reservoirs

history of earth s atmosphere
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

atmospheric composition average 1 ppm 1x10 6 red increased by human activity
Atmospheric Composition (average)1 ppm= 1x10-6red = increased by human activity

¶ Ozone has increased in the troposphere, but decreased in the stratosphere.

oxidation states of nitrogen n has 5 electrons in valence shell a 9 oxidation states from 3 to 5
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)

the nitrogen cycle major processes
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

box model of the nitrogen cycle
BOX MODEL OF THE NITROGEN CYCLE

Inventories in Tg N

Flows in Tg N yr-1

n 2 o low yield product of bacterial nitrification and denitrification
N2O: LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION AND DENITRIFICATION
  • Important as
    • source of NOx radicals in stratosphere
    • greenhouse gas

IPCC

[2007]

present day global budget of atmospheric n 2 o
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 )

box model of the n 2 o cycle

1.57 103 N2O

6

8

3

Inventories in Tg N

Flows in Tg N yr-1

BOX MODEL OF THE N2O CYCLE

12

oxidation states of sulfur s has 6 electrons in valence shell a oxidation states from 2 to 6
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)

the global sulfur cycle
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

fast oxygen cycle atmosphere biosphere
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

slide18
…however, abundance of organic carbon in biosphere/soil/ocean reservoirs is too small to control atmospheric O2 levels
slow oxygen cycle atmosphere lithosphere
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

atmospheric carbon
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

slide21

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

sinks of atmospheric methane
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

ipcc 2001 projections of future ch 4 emissions tg ch 4 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

1500

1000

2000

2020

2040

2000

Year

Year

slide24

Recent slow-down in growth rate

Pinatubo

Fires

Tropical wetlands

Low T / precip