Transcript Transpacific transport of anthropogenic aerosols and

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 University
April 26, 2006
RADIATIVE FORCING OF CLIMATE
Biogenic OC currently not included in forcing estimates  is it important?
ORGANIC CARBON AEROSOL
*Numbers from IPCC [2001]
Reactive
Organic
Gases
Secondary Organic
Aerosol (SOA): 8-40 TgC/yr
Nucleation or Condensation
OC
Oxidation
by OH, O3, NO3
Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
MEASURING OC IN THE ATMOSPHERE
CHALLENGE: To measure suite of compounds classified as organic carbon
Filter samples: Need to correct for volatilization of particles (negative
artifact) and adsorption of gas-phase organics (positive artifact)
Ambient Air
Denuder to
remove gas-phase
organics
Quartz
Filter (#1)
Backup (#2)
(to capture OC
evaporated from
filter #1)
Thermal Optical
analysis to determine
OC Concentration
DISTINGUISHING SOA FROM POA: EC/OC RATIO
Example from Pittsburg Air Quality Study [Cabada et al., 2004]
EC/OC ratio for primary
emissions are well-correlated
(triangles).
Deviations from the slope
are indicative of a secondary
OC source (squares).
Uncertainties:
• changing EC/OC emission ratios for sources
• mixing of air masses
DISTINGUISHING SOA FROM POA:
AEROSOL MASS SPECTROMETER (AMS)
m/z 57: hydrocarbon
like organic aerosol
 POA
m/z 44: oxygenated
organic aerosol
 SOA
Reduce complexity of observed spectra to 2 signals:
~2/3 of OC is SOA
(in urban site!)
[Zhang et al., 2005]
FIRST SUGGESTIONS OF HIGH ORGANIC CARBON
AEROSOL CONCENTRATIONS IN THE FREE TROPOSPHERE
High organic loading
in the FT
High organic loading
in the UT
Single particles over NA
[Murphy et al., Science, 1998]
TARFOX (E US)
[Novakov et al., JGR, 1998]
ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE
FREE TROPOSPHERE
(ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)
Seinfeld group
Huebert group
Russell group
What is the source
of this FT organic
carbon aerosol?
+
Mean Observations
Mean Simulation (GEOS-Chem global CTM)
Observations
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
DO WE UNDERSTAND OTHER AEROSOLS?
Secondary
production
Scavenging
Scavenging
Mean Observations
Mean Simulation (GEOS-Chem)
GEOS-Chem simulates both the magnitude and shape of sulfate and EC
concentrations throughout the troposphere  what is different about OC?
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
Secondary
Organic Aerosol
Condensation of
low vapour pressure
ROGs on preexisting aerosol
Reactive
Organic Gases
Oxidation by
OH, O3, NO3
SOA parameterization [Chung and Seinfeld, 2002]
VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j
Gi,j
Equilibrium (Komi,j)
 also f(POA)
Pi,j
Ai,j
Parameters (a’s K’s) from smog chamber studies
GEOS-CHEM April Biogenic SOA
Biogenic VOCs
(eg. monoterpenes)
FT observations ~ 4mg/m3
Biogenic SOA
far too small!
IMPLICATIONS FOR TRANSPACIFIC TRANSPORT
Observed
Simulated
Asian air masses
Sulfate: 0.24 µgm-3
OC: 0.53 µgm-3
ASIA
High concentrations of OC
aerosols measured in the FT
over Asia (not captured by models)
[Heald et al., 2005]
PACIFIC
NORTH
AMERICA
Twice as much OC
aerosol as sulfate
observed at Crater Lake
[Jaffe et al., 2005]
CARBON CYCLE AND POTENTIAL RADIATIVE
IMPLICATIONS
4 ug/sm3 (ACE-Asia)
AOD @ 50% RH: 0.057
TOA Radiative Forcing = -1.2 W/m2
OC AEROSOL
1 µg/sm3 from 2-7 km globally = 105 TgC/yr
VOC EMISSIONS
500-1000 TgC/yr
[IPCC, 2001]
DISSOLVED
ORGANIC CARBON
IN RAINWATER
430 TgC/yr
[Wiley et al., 2000]
ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY
CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH
ATLANTIC IN SUMMER 2004
Multi-agency,
International Collaboration
MOPITT Observations of CO Transport
(July 17-19) [Turquety et al., in prep]
2004 fire season in North America:
• worst fire season on record
in Alaska
Emissions derived from MODIS
hot spots [Turquety et al., in prep]
OC: 1.4 TgC
OC emissions from biomass burning were 4 times climatological average!
UNDERESTIMATE OF OC AEROSOL DURING ICARTT
Observed WSOC
GEOS-Chem WSOC
GEOS-Chem SOA
WS=water soluble
(10-80% of total OC, primarily SOA)
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].
BIOMASS BURNING & INJECTION HEIGHTS
Fires 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.
ITCT-2K4 “Background”
ITCT-2K4 BB plumes
Observations
GEOS-Chem Simulation
solid=60% injected
dashed=BL emissions
dotted=no BB
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.
UNDERESTIMATE AT SURFACE SITES AS WELL…
(IMPROVE network established in 1987 to monitor visibility in national parks)
IMPROVE
GEOS-Chem
Sulfate
OC
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]
GEIA Emissions July/August 2004
3% yield
= 0.4 Tg SOA
10% yield
= 0.8 Tg SOA
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.
INCLUDING ISOPRENE AS A SOURCE OF SOA:
COMPARISON WITH ITCT-2K4 OBSERVATIONS
Observed WSOC
Simulated WSOC
solid =SOA terpenes only
dotted = SOA terpenes+isoprene
Simulated SOA
solid =SOA terpenes only
dotted = SOA terpenes+isoprene
Including isoprene as a precursor to SOA formation (using low NOx yields)
leads to modest increase in SOA simulated over the northeastern NA.
SHARED CHEMICAL ORIGINS OF WSOC?
Correlation Coefficient Matrix
Note: BB plumes removed
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? 
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]
ITCT 2K4
Observations
GEOS-Chem Simulation
dashed: scavenging e=0.14
dottted: HSOG=103-107 M/atm
A large decrease in scavenging efficiency increases OC throughout
the troposphere, however this assumes a large degree of external mixing.
OTHER STUDIES SUGGESTING UNDERESTIMATE OF SOA
ANTHROPOGENIC ORGANIC
CARBON BUDGET
MEXICO CITY SURFACE OC
Growth in POM larger
than decrease In
aromatics
“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]
Surface measurements of OC also
underestimated at an urban polluted
location.
[Volkamer et al., 2006]
SMOG CHAMBER STUDIES: AMBIENT RELEVANCE
NITROGEN OXIDE LEVELS
TEMPERATURE
Cold Temperature Chemistry:
m-xylene photoxidation
decomposition
RO*
(alkoxy
radicals)
Add O2
aerosol
formation?
[Johnson et al., 2005]
[Song et al., 2005]
m-xylene photoxidation
Terpene ozonolysis
283K
SOA yield at 283K ~2x yield at 303K
303K
SOA yields  zero at VOC/NOx = 4.5
[Presto et al., 2005]
[Takekawa et al., 2005]
FORMATION MECHANISMS FOR ADDITIONAL SOA
OLIGOMERIZATION
CLOUD PROCESSING
2.5 hrs
VOC
TMB
4.5 hrs
Growth of higher mass
Oxidation
by OH
Evaporation
Mechanism for cloud-processing of
isoprene has been demonstrated in
the lab.
[Lim et al., 2005]
6.5 hrs
Polymerization (oligomerization)
produces higher mass compounds
with lower vapour pressure  SOA
[Kalberer et al., 2004]
UPTAKE OF GLYOXAL ON AEROSOLS
Uptake of glyoxal can increase SOA
by at least 15%
[Volkamer et al., 2006]
CONSTRAINTS FROM SATELLITES?
AEROSOL OPTICAL DEPTHS 2001/2005
MODIS
MISR
CAM
Community Atmospheric Model
(NCAR ESM with MOZART
chemistry)
Simulated AOD
overestimated over land
and underestimated over
oceans.
Retrieval uncertainties
larger than SOA signal.
MODIS/
MISR
Aerosols
Land
(difficult to characterize reflectance)
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
*Numbers from IPCC [2001]
Reactive
Organic
Gases
Secondary Organic
Aerosol (SOA): 8-40 TgC/yr
Nucleation or Condensation
OC
Oxidation
by OH, O3, NO3
Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
ORGANIC CARBON AEROSOL
Cloud
Processing
SOA: ?? TgC/yr
ROG
Nucleation or Condensation
OC
Heterogeneous Reactions
Oxidation
by OH, O3, NO3
Isoprene Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
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