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
Oxidation by OH, O3, NO3
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
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]
ORGANIC CARBON AEROSOL
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 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
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