Organic Carbon Aerosol

Colette L. Heald

University of California, Berkeley

NOAA Summer Institute, Steamboat Springs, COJuly 12, 2006

CURRENT UNDERSTANDING: SOURCES OF ORGANIC CARBON AEROSOL

ReactiveOrganicGases

Oxidation by OH, O3, NO3

Direct Emission

Fossil Fuel Biomass Burning

Monoterpenes

Nucleation or Condensation

Aromatics

ANTHROPOGENIC SOURCESBIOGENIC SOURCES

OC

FF: 45-80 TgC/yrBB: 10-30 TgC/yr

Secondary Organic Aerosol (SOA): 8-40 TgC/yr

*Numbers from IPCC [2001]

Formation and Transport

Emissions:1. Anthropogenic2. Natural/Biogenic

ORGANIC AEROSOLS: AIR QUALITY, CHEMISTRY AND CLIMATE

Air Quality Impacts:1. Visibility

2. Health

Climate Forcing1. Direct: Scatter solar radiation2. Indirect: ↑ cloud albedo

↑ cloud lifetime

ORGANIC CARBON AEROSOL: AT THE SURFACE

Organic carbon constitutes 10-70% of aerosol mass at surface.Difficult to distinguish primary from secondary contributions.

2004 NARSTO Assessment

ACE-ASIA: FIRST OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE

Mean ObservationsMean SimulationObservations+

Concentrations of OC in the FT were under-predicted by a factor of 10-100!

(ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)

GEOS-Chem:Global ChemicalTransport model

[Heald et al., 2005]

[Mader et al., 2002] [Huebert et al., 2003] [Maria et al., 2003]

CONTRAST: OTHER AEROSOLS IN ASIAN OUTFLOW

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

Mean ObservationsMean Simulation (GEOS-Chem)

Scavenging ScavengingSecondaryproduction

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.

No apparent underestimate in primary emissions

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

SECONDARY ORGANIC AEROSOL

Biogenic VOCs(eg. monoterpenes)

ReactiveOrganic Gases

Oxidation by OH, O3, NO3

SecondaryOrganic Aerosol

Condensation of low vapour pressure ROGs on pre-existing aerosol

Simulated April Biogenic SOA

FT observations ~ 4g/m3

Simulated SOA far too small!

SOA parameterization [Chung and Seinfeld, 2002]

VOCi + OXIDANTj i,jP1i,j + i,jP2i,j

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

Ai,j

GGi,ji,j

Pi,jEquilibrium (Komi,j) also f(POA)

SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA

[Volkamer et al., 2006]

Global underestimate in SOA?

OC AEROSOL OVER NORTH AMERICA: ICARTT CAMPAIGN

NOAA WP-3 Flight tracks

Note: biomass burning plumes were removed

OC aerosol concentrations captured by the model, BUT we cannot simulate variability in observations (R=0.21) incomplete understanding of formation.

ObservedSimulated

Water soluble OC Aerosol

OC aerosol concentrations 3x lower than observed off of Asia

[Heald et al., submitted]

2004: worst fire season on record in Alaska

Emissions derived from MODIS hot spots

[Turquety et al., submitted]

WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION?

ROG

Oxidation by OH, O3, NO3

Direct Emission

Monoterpenes

Nucleation or Condensation

Aromatics

OC

Isoprene

CloudProcessing

FF: 45-80 TgC/yrBB: 10-30 TgC/yr

SOA: ?? TgC/yr

Fossil Fuel Biomass Burning

ANTHROPOGENIC SOURCESBIOGENIC SOURCES

Heterogeneous ReactionsAdditionalPrecursors

1. Production moreefficient at low NOx2. Multi-step oxidation

New formation pathways

CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS

VOC EMISSIONS500-1000 TgC/yr

[IPCC, 2001]

DISSOLVED ORGANIC CARBON

IN RAINWATER430 TgC/yr

[Wiley et al., 2000]

OC AEROSOL1 µg/m3 from 2-7 km globally = 105 TgC/yr

4 μg/m3 (ACE-Asia)AOD @ 50% RH: 0.057

TOA Radiative Forcing = -1.2 W/m2

CURRENT WORK: HOW WILL SOA FORMATION RESPOND TO A FUTURE CLIMATE?

Biogenic Emissionsof precursors:T/light/moisture

Anthropogenic Emissions:Increasing aromatic emissionsMore surface area for aerosol condensation

Precipitation:Enhanced removal

Oxidant levels:Effected by

hydrological cycle and anthropogenic

pollution levels

Using a coupled land-atmosphere model

(NCAR CCSM)

ACKNOWLEDGEMENTS

Daniel Jacob, Rokjin Park, Solène Turquety, Rynda Hudman

Barry HuebertLynn Russell John Seinfeld, Hong Liao

Rodney Weber,Amy SullivanRick Peltier

ITCT-2K4 Science Team

Hosts: Inez Fung & Allen Goldstein