Black Carbon:Global Budget and Impacts on Climate

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Black CarbonGlobal Budget and Impacts on Climate
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Soot Particle from a Wood-Burning Stove
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Scanning electron microscope image of particles
collected in Xianghe, W of Beijing.
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Structure of Soot
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Outline

• Soot What is it?
• Climate Impact
• Physics
• Prior budgets
• INDOEX
• Budget evaluation
• Conclusions

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Climate forcing for atmospheric gases and
aerosolsIPCC (2001)
Forcing Agent Climate Forcing Wm-2 (Up to year 2000)
Greenhouse Gas
CO2 1.3 to 1.5
CH4 0.5 to 0.7
Tropos. O3 0.25 to 0.75
N2O 0.1 to 0.2
Fine Aerosol
SO4 2- 0.3 to 1.0
Black Carbon 0.1 to 0.8
Jacobson Nature, 2001.
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Radiation and fine particles
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Optical Properties Visibility

• Change in intensity of light reflecting off an
  object
• ?I / I exp(-bext ?X)
• where I incident intensity of light
• ?I change in intensity of light
• bext extinction coefficient (m-1)
• ?X distance (m)

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Extinction Coefficient, bext

• Sum of scattering and absorption coefficients
• bext bscat babs
• Decomposed further from gases and particles
• babs bag bap
• bscat bsg bsp
• Where
• bag absorption coefficient due to gases
  (Beer's law)
• bap absorption coefficient due to particles
• bsg scattering coefficient due to gases
  (Rayleigh scattering)
• bsp scattering coefficient due to particles
  (Mie scattering)

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Atmospheric Aerosols
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Optical Properties of Small Particles

• bscat/bext
• Single scattering albedo
• m n ik
• m complex index of refraction
• n scattering (real part)
• k absorption (imaginary part)

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Refractive indicies of aerosol particles at ?
589 nm
m n ik
Substance n k
Water 1.333 10-8
Ice 1.309 10-8
NaCl 1.544 0
H2SO4 1.426 0
NH4HSO4 1.473 0
(NH4)2SO4 1.521 0
SiO2 1.55 0
Black Carbon (soot) 1.96 0.66
Mineral dust 1.53 0.006
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Radiative Effects (Climate Impact) of Soot

• External mixture 0.27 Wm-2
• Coated core 0.54 Wm-2
• Well-mixed internally 0.78 Wm-2
• (Jacobson, GRL., 2000)

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External vs. Internal Mixtures
Sulfate Soot mixed externally.
Soot with sulfate coating (coated core).
Well-mixed internally.
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Global Fossil Fuel Black Carbon Emissions(Cooke
et al., JGR., 1999 Penner et al., 1993)
Region BC Emissions Tg yr-1
W. Europe 0.58
Eastern Europe 0.68
Africa 0.17
N. America 0.49
C. S. America 0.26
Former USSR 0.69
China Oceania 1.18
Rest of Asia 0.89
Total fossil fuel 5.06
Biomass Burning 5.97
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Indian Today, 1996
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INDOEX, 1999
INDOEX Experimental Design
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NOAA R/V Ronald Brown
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Impactor Samples from Ship during INDOEX
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Origin of Soot?

• Ratio of BC/OC near unity means origin should be
  fossil fuel
• combustion (Novakov et al., 2001).

• Low single scattering albedo, 0.81, indicates 70
  from fossil
• fuel combustion (Mayol-Bracero et al, 2001).

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Emissions InventoriesGg yr-1 Black Carbon from
South AsiaHigh Estimate for 1999
Industry Domestic Mobile Sources Power Generation Field Combustion Total
263 550 139 2.7 37 1009
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Estimate of BC Emissionfrom Ambient Measurements
EBC ECOBC/CO/LBC Fort Meade, MD EBC 90
Tg(CO)/yr 0.0034 0.31 Tg(BC)/yr for N
America (vs. 0.49 Tg(BC)/yr) INDOEX EBC 87
Tg(CO)/yr 0.0125/0.5 2.2 Tg(BC)/yr for South
Asia (vs. 0.5 to 1Tg(BC)/yr)
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Two-Stroke Engine

• No Valves
• Oil mixed with gasoline
• Part of fresh charged exhausted
• Fuel adulteration

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Source Strength Black Carbon in China
Estimated annual BC emissions from
China 1300-2600 Gg/yr Inventory 1049 Gg/yr
Streets et al., 2003 Better agreement compared
to a similar study for India Dickerson et al.,
2002
Single Scattering Albedo (SSA) Morning 0.81,
Afternoon 0.85
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• The ambient EC concentration decreases 50 in
  the recent 11 years.

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• The ambient OC concentration decreases 10 in
  the recent 11 years.

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• EC and OC are correlated (95-00) but show no
  obvious trend.

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• EC shows a decreasing trend but no correlation
  with OC.

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• At SHEN, EC decrease by 15 in 8 years
  (1989-1997) while CO decrease by 20 during the
  same period.

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Summary

• Black Carbon (soot) may provide more forcing than
  methane.
• Properties of aerosols suggest that fossil fuel
  combustion is main source of black carbon from
  South Asia.
• Inventories suggest biofuels contribute
  substantially, and cannot support emissions above
  1 Tg(BC) a-1.
• Ambient measurements suggest major role for
  biomass burning and indicate 2-3 Tg(BC) a-1.
• Combustion in S Asia is unlike anything seen in N
  America or Europe.
• Time for direct measurements.

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Black Carbon References