Organic Carbon Aerosol: Insights from the ACE-Asia and ICARTT field campaigns

Organic Carbon Aerosol:Insights from the ACE-Asia and ICARTT field campaigns

Colette L. Heald([email protected])

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

Stony Brook UniversityApril 26, 2006

RADIATIVE FORCING OF CLIMATE

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

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]

MEASURING OC IN THE ATMOSPHERE

Ambient AirDenuder to

remove gas-phaseorganics

Quartz Filter (#1)

Backup (#2)(to capture OC

evaporated from filter #1)

Filter samples: Need to correct for volatilization of particles (negative artifact) and adsorption of gas-phase organics (positive artifact)

Thermal Optical analysis to determine

OC Concentration

CHALLENGE: To measure suite of compounds classified as organic carbon

DISTINGUISHING SOA FROM POA: EC/OC RATIO

Example from Pittsburg Air Quality Study [Cabada et al., 2004]

EC/OC ratio for primaryemissions are well-correlated(triangles).

Deviations from the slopeare indicative of a secondaryOC source (squares).

Uncertainties:• changing EC/OC emission ratios for sources• mixing of air masses

DISTINGUISHING SOA FROM POA:AEROSOL MASS SPECTROMETER (AMS)

Reduce complexity of observed spectra to 2 signals:

[Zhang et al., 2005]

~2/3 of OC is SOA (in urban site!)

m/z 44: oxygenated organic aerosol

SOA

m/z 57: hydrocarbonlike organic aerosol

POA

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 organic loadingin the FT

ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE

Mean ObservationsMean Simulation (GEOS-Chem global CTM)Observations+

What is the sourceof this FT organiccarbon aerosol?

High Levels of OC were observed in the FT during ACE-Asia by 2 independent measurement techniques. We cannot simulate this OC with direct emissions

Seinfeld group Huebert group Russell group

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

DO WE UNDERSTAND OTHER AEROSOLS?

GEOS-Chem simulates both the magnitude and shape of sulfate and ECconcentrations throughout the troposphere what is different about OC?

Mean ObservationsMean Simulation (GEOS-Chem)

Scavenging ScavengingSecondaryproduction

ANY INDICATION THAT DIRECT EMISSIONS ARE UNDERESTIMATED?

Biomass Burning:• Satellite firecounts show no active fires in Siberia• OC aerosol from agricultural burning in SE Asia emitted earlier in the season, at lower latitudes and is not injected into the FT

Pollution:• Although the highest aerosol observations are associated with elevated CO, there is a free tropospheric background of 1-3 μg sm-3 that is not correlated with CO or sulfate.

SECONDARY ORGANIC AEROSOL SIMULATION

Biogenic VOCs(eg. monoterpenes)

ReactiveOrganic Gases


SecondaryOrganic Aerosol

Condensation of low vapour pressure ROGs on pre-existing aerosol

SOA parameterization [Chung and Seinfeld, 2002]

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

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

FT observations ~ 4g/m3

Biogenic SOA far too small!

Ai,j

GGi,ji,j

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

GEOS-CHEM April Biogenic SOA

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

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/sm3 from 2-7 km globally = 105 TgC/yr

4 ug/sm3 (ACE-Asia)AOD @ 50% RH: 0.057

TOA Radiative Forcing = -1.2 W/m2

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., in prep]

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., in prep]

UNDERESTIMATE OF OC AEROSOL DURING ICARTT

NOAA ITCT-2K4 flight tracks(R. Weber’s PILS instrument aboard)

Note: biomass burning plumes were removed

OC aerosol underestimate observed over North America as well

[Heald et al., in prep].

WS=water soluble (10-80% of total OC, primarily SOA)Observed WSOC

GEOS-Chem WSOCGEOS-Chem SOA

BIOMASS BURNING & INJECTION HEIGHTSFires over boreal regions generate enough energy to inject emissions into FT.Following Turquety et al. [in prep], we inject 60% of emissions directly into FT

(3-5km) thus avoiding scavenging during lifting.

Large contribution of WSOC from boreal fires in plumes and background. Injection of BB emissions into the FT increases the OC observed in the FT

down-wind. Model may underestimate boreal fires, or overestimate scavenging or dilution.

ITCT-2K4 “Background”

ObservationsGEOS-Chem Simulation solid=60% injected dashed=BL emissions dotted=no BB

ITCT-2K4 BB plumes

UNDERESTIMATE AT SURFACE SITES AS WELL…

Sulfate

OC

IMPROVE GEOS-Chem

(IMPROVE network established in 1987 to monitor visibility in national parks)

Uniform ~0.9 μgCm-3 underestimate in OC across the U.S. Smaller contribution from Alaskan boreal fires at the surface than aloft.

INCLUDING ISOPRENE AS A SOURCE OF SOA

Recent study: yield of SOA from isoprene is 0.9-3.0%[Kroll et al., 2005].Isoprene oxidation products have been observed in the particulate phase

[Claeys et al., 2004; Matsunaga et al., 2005]

Isoprene is the second most abundant hydrocarbon emitted to the atmosphere (~500 Tg/yr). Even with a modest yield this could be an

important source of SOA.

GEIA Emissions July/August 2004

3% yield = 0.4 Tg SOA

10% yield = 0.8 Tg SOA

INCLUDING ISOPRENE AS A SOURCE OF SOA: COMPARISON WITH ITCT-2K4 OBSERVATIONS

Including isoprene as a precursor to SOA formation (using low NOx yields)leads to modest increase in SOA simulated over the northeastern NA.

Observed WSOCSimulated WSOC solid =SOA terpenes only dotted = SOA terpenes+isopreneSimulated SOA solid =SOA terpenes only dotted = SOA terpenes+isoprene

SHARED CHEMICAL ORIGINS OF WSOC?

No single species can explain more than 16% of the variability in WSOC.Toluene in combination with other tracers can explain over half the variability.

Anthropogenic SOA?

Note: BB plumes removed

Correlation Coefficient Matrix

IS SCAVENGING OF OC AEROSOLS OVERESTIMATED IN MODELS?

Hydrophillic aerosols are wet scavenged assuming 100% solubility.Recent analysis of cloud events at Puy de Dome suggest scavenging efficiency of

OC is much lower [Sellegri et al., 2003].However aerosols observed at Jungfraujoch are internally mixed [Baltensperger]

A large decrease in scavenging efficiency increases OC throughout the troposphere, however this assumes a large degree of external mixing.

ITCT 2K4

ObservationsGEOS-Chem Simulation

dashed: scavenging =0.14dottted: HSOG=103-107 M/atm

OTHER STUDIES SUGGESTING UNDERESTIMATE OF SOA

ANTHROPOGENIC ORGANIC CARBON BUDGET

“The increase in sub-µm POM could not be explained by the removal of

aromatic precursors alone, suggesting that other species must have

contributed and/or that the mechanism for POM formation is more efficient

than previously assumed.”

[de Gouw et al., 2005]

Growth in POM largerthan decrease In

aromatics

[Volkamer et al., 2006]

MEXICO CITY SURFACE OC

Surface measurements of OC alsounderestimated at an urban polluted

location.

SMOG CHAMBER STUDIES: AMBIENT RELEVANCE

[Presto et al., 2005]

NITROGEN OXIDE LEVELS TEMPERATURE

[Takekawa et al., 2005]

[Johnson et al., 2005]

Terpene ozonolysis

303K

283K

m-xylene photoxidation

SOA yield at 283K ~2x yield at 303K

Cold Temperature Chemistry:

RO*(alkoxy radicals)

decomposition

Add O2aerosol

formation?

SOA yields zero at VOC/NOx = 4.5

[Song et al., 2005]

m-xylene photoxidation

FORMATION MECHANISMS FOR ADDITIONAL SOA

[Kalberer et al., 2004]

OLIGOMERIZATION

[Volkamer et al., 2006]

Polymerization (oligomerization) produces higher mass compounds with lower vapour pressure SOA

2.5 hrs

4.5 hrs

6.5 hrs

Growth of higher mass

TMB

UPTAKE OF GLYOXAL ON AEROSOLS

Uptake of glyoxal can increase SOA by at least 15%

CLOUD PROCESSING

EvaporationOxidation by OH

[Lim et al., 2005]

VOC

Mechanism for cloud-processing of isoprene has been demonstrated in

the lab.

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

CONSTRAINTS FROM SATELLITES?GLYOXAL: AROMATIC OXIDATION PRODUCT

Space-based observations can test:1. Evidence of glyoxal uptake on aerosols?2. General test on VOC chemistry

Courtesy: Rainer Volkamer

BEFORE: ORGANIC CARBON AEROSOL

ReactiveOrganicGases


Direct Emission


Monoterpenes


Aromatics


OC


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

*Numbers from IPCC [2001]

ORGANIC CARBON AEROSOL

ROG


Direct Emission

Monoterpenes


Aromatics

OC

Isoprene

CloudProcessing


SOA: ?? TgC/yr



Heterogeneous Reactions

CONCLUSIONS

• Concentrations observed in the FT off of Asia during ACE-Asia were 1-2 orders of magnitude greater than simulated.– Cannot be reconciled with uncertainties in current models– Important implications for transpacific transport

• Concentrations of WSOC observed over NE North America during ITCT-2K4 were underestimated by a factor of 2– Much larger biomass burning influence – No clear indication from the observations on the source of

background OC in the free troposphere anthropogenic SOA?– Uncertainties in sources and sinks can resolve the disagreement

• Processes leading to SOA formation not clearly understood and not captured with current model parameterizations. Expect that estimates of the global source of SOA will be revised upwards.

FUNDING ACKNOWLEDGEMENTS: EPA, EPRI, NASA ESS Fellowship, NOAA Global & Climate Change Postdoctoral Fellowship

Documents

Organic Carbon Aerosol: Insights from the ACE-Asia and ICARTT field campaigns