Organic Carbon Aerosol:Insight from recent aircraft field campaigns

Colette L. HealdNOAA Climate and Global Change Postdoctoral Fellow

(heald@atmos.berkeley.edu)

Department of Civil and Environmental Engineering, Stanford UniversityOctober 27, 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

LA

Particulates contribute to urban smog:

[Environmental Working Group Report, 2005]

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

Biogenic 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

OBSERVING TROPOSPHERIC COMPOSITION ON ALL SCALES

SATELLITESAIRCRAFT CAMPAIGNSSURFACE SITES

Long-term monitoringat the surface

Chemical characterizationthroughout the

troposphere

Continuous,global

measurements

AIR QUALITY CLIMATE

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

FIRST SUGGESTIONS OF HIGH ORGANIC CARBON AEROSOL CONCENTRATIONS IN THE FREE TROPOSPHERE

Single particles over NA [Murphy et al., Science, 1998]

High organic loadingin the UT

TARFOX (E US) [Novakov et al., JGR, 1998]

High organicloading

in the FT

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 during ACE-Asia

Mean ObservationsMean Simulation (GEOS-Chem)

Scavenging ScavengingSecondaryproduction

Sulfate Elemental Carbon

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 indication of a primary source for OC in FT

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)

IMPLICATIONS FOR TRANSPACIFIC TRANSPORT

NORTHAMERICA

ASIA

High concentrations of OCaerosols measured in the FT

over Asia (not captured by models)[Heald et al., 2005]

ObservedSimulated

Asian air massesSulfate: 0.24 µgm-3

OC: 0.53 µgm-3

Twice as much OC aerosol as sulfate

observed at Crater Lake[Jaffe et al., 2005]

PACIFIC

SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA

[Volkamer et al., 2006]

Global underestimate in SOA?

ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH

ATLANTIC IN SUMMER 2004 2004 fire season in North America:

• worst fire season on record in Alaska

Multi-agency, International Collaboration

Emissions derived from MODIS hot spots [Turquety et al., submitted]

OC emissions from biomass burning were 4 times climatological average!

OC: 1.4 TgC

MOPITT Observations of CO Transport (July 17-19) [Turquety et al., submitted]

WHAT CONTRIBUTES TO OC AEROSOL OVER NORTH AMERICA?

NOAA WP-3 Flight tracksObserved boreal fireInfluence down-wind

Simulated source attribution for “background” OC

*includes isoprene as a source of SOA [Kroll et al., 2005]

OC concentrations in the free troposphere doubled as a result of Alaskan boreal fires. Is model attribution of remaining OC sources correct?

BB filtered using CH3CN

DO WE UNDERSTAND OC AEROSOL OVER NORTH AMERICA?

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.

OC aerosol concentrations 3x lower than observed off of Asia

[Heald et al., accepted]

ObservedSimulated

Sulfur Oxides (SOx) Water soluble OC Aerosol (WSOC)

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

CONSTRAINTS FROM SATELLITES?AEROSOL OPTICAL DEPTHS 2001/2005

Simulated AOD overestimated over land and underestimated over

oceans.

Retrieval uncertainties larger than SOA signal.

MODIS MISR CAM Community Atmospheric Model (NCAR ESM with MOZART chemistry)

Land (difficult to characterize reflectance)

MODIS/MISR

Aerosols

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

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)

Land Use Change

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