Organic Carbon Aerosol

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Organic Carbon Aerosol
Colette L. Heald University of California,
Berkeley
NOAA Summer Institute, Steamboat Springs, CO July
12, 2006
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CURRENT UNDERSTANDING SOURCES OF ORGANIC CARBON
AEROSOL
Numbers from IPCC 2001
Secondary Organic Aerosol (SOA) 8-40 TgC/yr
Reactive Organic Gases
Nucleation or Condensation
OC
Oxidation by OH, O3, NO3
FF 45-80 TgC/yr BB 10-30 TgC/yr
Monoterpenes
Aromatics
Direct Emission
Fossil Fuel Biomass
Burning
ANTHROPOGENIC SOURCES
BIOGENIC SOURCES
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ORGANIC AEROSOLS AIR QUALITY, CHEMISTRY AND
CLIMATE
Climate Forcing 1. Direct Scatter solar
radiation 2. Indirect ? cloud albedo ?
cloud lifetime
Formation and Transport

• Air Quality
• Impacts
• Visibility
• Health

• Emissions
• Anthropogenic
• Natural/Biogenic

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ORGANIC CARBON AEROSOL AT THE SURFACE
2004 NARSTO Assessment
Organic carbon constitutes 10-70 of aerosol mass
at surface. Difficult to distinguish primary from
secondary contributions.
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ACE-ASIA FIRST OC AEROSOL MEASUREMENTS IN THE
FREE TROPOSPHERE
(ACE-Asia aircraft campaign conducted off of
Japan during April/May 2001)
Mader et al., 2002
Huebert et al., 2003
Maria et al., 2003
GEOS-Chem Global Chemical Transport model
Concentrations of OC in the FT were
under-predicted by a factor of 10-100!
Heald et al., 2005
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CONTRAST OTHER AEROSOLS IN ASIAN OUTFLOW
Secondary production
Scavenging
Scavenging
Model simulates both the magnitude and profile of
sulfate and elemental carbon (EC) during ACE-Asia
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ANY INDICATION THAT DIRECT EMISSIONS ARE
UNDERESTIMATED?

• Biomass Burning
• Satellite firecounts show no active fires in
  Siberia
• Agricultural fires in SE Asia do not contribute
  in the FT.

• Pollution
• There is a free tropospheric background of 1-4
  µg sm-3 that is not correlated with CO or sulfate.

No apparent underestimate in primary emissions
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SECONDARY ORGANIC AEROSOL
Secondary Organic Aerosol
Condensation of low vapour pressure ROGs on
pre- existing aerosol
Reactive Organic Gases
Oxidation by OH, O3, NO3
Simulated April Biogenic SOA
Biogenic VOCs (eg. monoterpenes)
FT observations 4mg/m3 Simulated SOA far too
small!
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SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA
Volkamer et al., 2006
Global underestimate in SOA?
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OC AEROSOL OVER NORTH AMERICA ICARTT CAMPAIGN
Emissions derived from MODIS hot spots
Turquety et al., submitted
NOAA WP-3 Flight tracks
Water soluble OC Aerosol
Observed Simulated
2004 worst fire season on record in Alaska
OC aerosol concentrations 3x lower than observed
off of Asia
OC aerosol concentrations captured by the model,
BUT we cannot simulate variability in
observations (R0.21) ? incomplete understanding
of formation.
Heald et al., submitted
Note biomass burning plumes were removed
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WHAT DONT WE UNDERSTAND ABOUT SOA FORMATION?
Cloud Processing
1. Production more efficient at low NOx 2.
Multi-step oxidation
SOA ?? TgC/yr
New formation pathways
Nucleation or Condensation
OC
ROG
Heterogeneous Reactions
Additional Precursors
Oxidation by OH, O3, NO3
FF 45-80 TgC/yr BB 10-30 TgC/yr
Monoterpenes
Aromatics
Isoprene
Direct Emission
Fossil Fuel Biomass
Burning
ANTHROPOGENIC SOURCES
BIOGENIC SOURCES
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CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS
4 µg/m3 (ACE-Asia) AOD _at_ 50 RH 0.057 TOA
Radiative Forcing -1.2 W/m2
OC AEROSOL 1 µg/m3 from 2-7 km globally 105
TgC/yr
DISSOLVED ORGANIC CARBON IN RAINWATER 430 TgC/yr
Wiley et al., 2000
VOC EMISSIONS 500-1000 TgC/yr IPCC, 2001
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CURRENT WORK HOW WILL SOA FORMATION RESPOND TO A
FUTURE CLIMATE?
Using a coupled land-atmosphere model (NCAR CCSM)
Oxidant levels Effected by hydrological cycle
and anthropogenic pollution levels
Precipitation Enhanced removal
Biogenic Emissions of precursors T/light/moisture
Anthropogenic Emissions Increasing aromatic
emissions More surface area for aerosol
condensation
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ACKNOWLEDGEMENTS
Daniel Jacob, Rokjin Park, Solène Turquety, Rynda
Hudman
Barry Huebert
John Seinfeld, Hong Liao
Lynn Russell
Rodney Weber, Amy Sullivan Rick Peltier
ITCT-2K4 Science Team
Hosts Inez Fung Allen Goldstein