Investigating the Sources of Organic Carbon Aerosol in the Atmosphere

Colette L. HealdNOAA Climate and Global Change Postdoctoral Fellow

University of California, Berkeley(heald@atmos.berkeley.edu)

Daniel J. Jacob, Rokjin J. Park, Solène Turquety, Rynda C. Hudman, Rodney J. Weber, Rick Peltier, Amy Sullivan, Lynn M. Russell

Barry J. Huebert, John H. Seinfeld, Hong Liao

Young Scientists’ Global Change Conference, BeijingNovember 7, 2006

AEROSOL IMPACTS ON AIR QUALITY

AIR QUALITY / HEALTH VISIBILITY

Clear Day

April 16, 2001

Visibility reduction at Glen Canyon, Arizona due to transpacific transport of Asian dust

Particulates contribute to urban smog:

[Environmental Working Group Report, 2005]

Beijing

AEROSOL IMPACTS ON CLIMATE

DIRECT EFFECT INDIRECT EFFECT

1. Scattering Radiation = COOLING

2. Absorbing Radiation = WARMING

Reflection

Refraction

Absorption

Increase cloud albedo = COOLINGIncrease cloud lifetime = COOLING

ESTIMATED RADIATIVE FORCING OF CLIMATE

Secondary OC currently not included in forcing estimates is it important?

[IPCC, 2001]

ORGANIC CARBON AEROSOL

ReactiveOrganicGases

Oxidation by OH, O3, NO3

Direct Emission

Fossil Fuel Biomass Burning

Monoterpenes

Nucleation or Condensation

Aromatics

ANTHROPOGENIC SOURCESBIOGENIC SOURCES

OC

Fossil Fuel: 10-30 TgC/yrBiomass Burning: 45-80 TgC/yr

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

*Numbers from IPCC [2001]

Isoprene

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 Reactions1. Precursors

2. Chemistry• Production more efficient at low NOx • Multi-step oxidation

3. 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 in the FT globally ~ 100 TgC/yr

AOD @ 50% RH: 0.014TOA Radiative Forcing = -0.3 W/m2