Organic Carbon Aerosol

Colette L. Heald University of California, Berkeley

NOAA Summer Institute, Steamboat Springs, CO July 12, 2006

CURRENT UNDERSTANDING: SOURCES OF ORGANIC CARBON AEROSOL *Numbers from IPCC [2001] Reactive Organic Gases Secondary Organic Aerosol (SOA): 8-40 TgC/yr Nucleation or Condensation OC Oxidation by OH, O 3 , NO 3 Monoterpenes Aromatics FF: 45-80 TgC/yr BB: 10-30 TgC/yr Direct Emission BIOGENIC SOURCES Fossil Fuel Biomass Burning ANTHROPOGENIC SOURCES

ORGANIC AEROSOLS: AIR QUALITY, CHEMISTRY AND CLIMATE Climate Forcing 1. Direct: Scatter solar radiation 2. Indirect: ↑ cloud albedo ↑ cloud lifetime Formation and Transport Emissions: 1. Anthropogenic 2. Natural/Biogenic Air Quality Impacts: 1. Visibility 2. Health

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.

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] +

Mean Observations Mean Simulation Observations

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]

CONTRAST: OTHER AEROSOLS IN ASIAN OUTFLOW Secondary production Scavenging Scavenging

Mean Observations Mean Simulation (GEOS-Chem)

Model simulates both the magnitude and profile of sulfate and elemental carbon (EC) during ACE-Asia

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

SECONDARY ORGANIC AEROSOL Secondary Organic Aerosol SOA parameterization

[

Chung and Seinfeld

, 2002]

VOC i + OXIDANT j

 a

i,j P1 i,j +

a

i,j P2 i,j Condensation of low vapour pressure ROGs on pre existing aerosol Reactive Organic Gases P i,j G i,j

Equilibrium (Kom i,j )  also f(POA)

A i,j

Parameters ( a ’s K’s) from smog chamber studies

Oxidation by OH, O 3 , NO 3 Simulated April Biogenic SOA Biogenic VOCs (eg. monoterpenes) FT observations ~ 4

m

g/m 3 Simulated SOA far too small!

SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA Global underestimate in SOA?

[

Volkamer et al

., 2006]

OC AEROSOL OVER NORTH AMERICA: ICARTT CAMPAIGN NOAA WP-3 Flight tracks Emissions derived from MODIS hot spots [Turquety et al., submitted] 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 (R=0.21)



incomplete understanding of formation.

Note: biomass burning plumes were removed [

Heald et al

., submitted]

WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION?

1. Production more efficient at low NOx 2. Multi-step oxidation Additional Precursors

Cloud Processing

New formation pathways

Nucleation or Condensation ROG Heterogeneous Reactions Oxidation by OH, O 3 , NO 3 Isoprene Monoterpenes Aromatics SOA: ?? TgC/yr OC FF: 45-80 TgC/yr BB: 10-30 TgC/yr Direct Emission BIOGENIC SOURCES Fossil Fuel Biomass Burning ANTHROPOGENIC SOURCES

CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS

4 μg/m 3 (ACE-Asia)

AOD @ 50% RH: 0.057

TOA Radiative Forcing = -1.2 W/m 2 OC AEROSOL

1 µg/m 3 from 2-7 km globally =

105 TgC/yr VOC EMISSIONS 500-1000 TgC/yr

[IPCC, 2001]

DISSOLVED ORGANIC CARBON IN RAINWATER 430 TgC/yr

[Wiley et al., 2000]

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

Biogenic Emissions of precursors:

T/light/moisture

Anthropogenic Emissions: Precipitation:

Enhanced removal Increasing aromatic emissions More surface area for aerosol condensation

ACKNOWLEDGEMENTS

Daniel Jacob, Rokjin Park, Sol ène Turquety, Rynda Hudman Barry Huebert Lynn Russell Rodney Weber, Amy Sullivan Rick Peltier ITCT-2K4 Science Team John Seinfeld, Hong Liao Hosts: Inez Fung & Allen Goldstein