Secondary Organic Aerosols: What we know and current CAM treatment
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Transcript of Secondary Organic Aerosols: What we know and current CAM treatment
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Secondary Organic Aerosols:What we know and current CAM treatment
Chemistry-Climate Working Group Meeting, CCSMMarch 22, 2006
Colette L. Heald([email protected])
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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]
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IN THE LAB: SMOG CHAMBER EXPERIMENTS
oMYield
HC
Teflon Chamber
20-30°COxidant (OH, O3, NO3)
High NOxVOC eg. -pinene
dryseed particles eg. (NH3)2SO4
SOAformation
Biogenic terpenes: yield 2-67%[Griffin et al., 1999]
oMYield
HC
Wallloss
Issues:1. High VOC concentrations2. High oxidant and NOx concentrations3. Relatively high (generally fixed) T
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Two Product Model [Odum et al., 1997]: ROGi + OXIDANTj i,jP1i,j + i,jP2i,j
• once formed the semi-volatile reaction products (P) will partition b/w gas and aerosol phase (as governed by the equilibrium partition coefficient (Kom)
• fitting parameters (’s and K’s) from smog chamber data
• partition coefficients are temperature sensitive (use Clausius-Clapeyron eqn)
• at each time-step solve for equilibrium
IN A MODEL: SOA PARAMETERIZATION [Chung and Seinfeld, 2002]
, ,, ,
, , , 0
[ ][ ] i j k
i j kom i j k
AG
K M
[G] =product (gas) or SOG[A] = product (aerosol) or SOAMo = concentration of total organic aerosol
, , , 2 , ,2
, , , 1 1 2 1
( ) 1 1exp
( )om i j k i j k
om i j k
K T HT
K T T R T T
H= enthalpy of vaporization
ROG = 5 biogenic HC classes (terpenes and ORVOCs)OXIDANT = OH, O3, NO3
Carry both gas and aerosol phase products as tracers
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IN CAM: SIMPLIFIED 2-PRODUCT FORMULATION[Lack et al., 2004]
For < 0.2 μg/m3 pre-existing OC: use bulk yield
For > 0.2 μg/m3: partition using two product model• take parameters from smog chamber data• ultimate yield calculated as:
• No temperature dependence on partitioning corrected
• Add newly formed SOA to pre-existing
i iom
iomi
MK
KMY
0,
,0 1
ROG = terpenes (C10H16), toluene and big alkanes (> heptane)OXIDANTS = OH, O3, NO3
Carry only lumped SOA product
ADVANTAGE: one SINGLE tracer (for as many precursors as we want)DISADVANTAGE: not representing equilibrium processQUESTION: Is additional complexity warranted?
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ACE-ASIA: OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE
Mean ObservationsMean Simulation (GEOS-Chem [Park et al., 2003])Observations+
High Levels of OC were observed in the FT during ACE-Asia by 2 independent measurement techniques. We cannot simulate this OC with current models
[Heald et al., 2005].
Seinfeld group Huebert group Russell group
(ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)
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UNDERESTIMATE OF OC AEROSOL DURING ICARTT
NOAA ITCT-2K4 flight tracks(R. Weber’s PILS instrument aboard)
Observations GEOS-Chem Simulation
Note: biomass burning plumes were removed
OC aerosol underestimate observed over North America as well
[Heald et al., in prep].
SOA
WSOMC
OMC (=POA+SOA)
OMC=organic molecular carbon (=1.4xOC)WS=water soluble (10-80% of total OC, primarily SOA)
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Evap
ISOPRENE AS A SOURCE OF SOA
Pandis et al., 1991
NO SOA observed
Kroll et al., 2005
Yield = 0.9-3.0%
Edney et al., 2005
NO SOA observedunless SO2 present
Claeys et al., 2004
Observed tetrols (ox product of isoprene)
Propose: acid-catalysedreaction w/ H2O2
Matsunaga et al., 2005
Observed ox productsof isoprene in particulate
phase.Propose: polymerization
Lim et al., 2004
Cloud processing of Isoprene supported by lab experiments
SmogChamber
SmogChamber
SmogChamber
Ox VOC
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.
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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]
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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
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SOA FORMATION: PROCESSES TO CONSIDER
HC + oxidant + Condensation
1. Multiple oxidation steps (explicit chemistry)2. Isoprene as a source of SOA [Kroll et al., 2005; Henze et al., submitted]3. Effect of NOx concentrations LAB4. Temperature-dependence of formation LAB5. Uptake on inorganic aerosols LAB6. Polymerization reactions LAB7. Heterogeneous reactions LAB8. Cloud processing
Current plan for CAM:1. Add isoprene as a source of SOA using 2-product framework2. Put latest MEGAN biogenic emission model in CLM to drive CAM3. Look at sensitivity of SOA formation to climate change
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SOx CONCENTRATIONS: IMPROVE SITES (1988-2004)
Sulfate concentrations
in the US overestimated
with Mozart wetdep
Mozart wetdep CAM wetdep
SO2
SO4
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SULFATE COMPARISONS: U MIAMI SITES (1981-1998)Mozart wetdep
CAM wetdep
μg/m3
Sulfate concentrations globally reasonable for both simulations (less bias with CAM wetdep)
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OC CONCENTRATIONS: IMPROVE SITES (1988-2004)
Mozart wetdep CAM wetdep
OC comparison with observations over the US not definitive…
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AEROSOL OPTICAL DEPTH COMPARISON (2001/2005)
Less wet deposition in Mozart increases AOD better match with satellitesover water, but overestimate over land
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AOD COMPARISONS: AERONET SITES (1992-2005)
Mozart wetdep CAM wetdep Mozart wetdep CAM wetdep
CAM wet deposition
better representation of magnitude
and seasonality at
all sites.
Note that both simulations
show excessive
aerosol transport over
oceans.
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SEASONAL CYCLE: AOD COMPARISONSLAND OCEAN
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FORMATION OF SOA
A1,A2,...,An
G1,G2,...,GnVOC + ox P1, P2, …Pn
AQ1,AQ2,...,AQn
Partitioning Theory Henry’s Law and Dissociation
Hi = iaq
AQi/Gi
AQi AQi- AQi
2-Gi
Ai / MoKom,iRT
poL,i MWomi
Griffin et al. (2003)
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FIRST SUGGESTIONS OF HIGH ORGANIC CARBON AEROSOL CONCENTRATIONS IN THE FT
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
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ACE-ASIA: MODEL REPRODUCES OTHER AEROSOL PROFILES
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)
Secondaryproduction Scavenging Scavenging
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ACE-ASIA: SECONDARY ORGANIC AEROSOL UNDERESTIMATED?
Biogenic VOCs(eg. monoterpenes)
ReactiveOrganic Gases
Oxidation by OH, O3, NO3
SecondaryOrganic Aerosol
Condensation of low vapour pressure ROGson pre-existing aerosol
SOA is a good candidate:condense more easily with colder temperature
AND be produced in the FT (escape scavenging)
GEOS-CHEM April Biogenic SOA
FT observations ~ 4g/m3
Simulated biogenic SOA far too small!
[Chung and Seinfeld, 2002]mechanism
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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]
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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]
Applying smog chamber estimates [Kroll et al., 2005] to isoprene emissions inventories suggests a 50% increase in the SOA source over NA.
GEIA Emissions July/August 2004
3% yield = 0.4 Tg SOA
10% yield = 0.8 Tg SOA
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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 may be much lower [Sellegri et al., 2003].
A large decrease in scavenging efficiency increases OMC concentrations throughout the troposphere. To what degree are OC aerosols internally mixed?
ITCT 2K4 OMC ObservationsGEOS-Chem SimulationGEOS-Chem Simulation (with scavenging =0.14)
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CLIMATOLOGICAL DIRECT EMISSIONS FROM ASIA
% ofGlobal
Emissions31% 41% 32% 20% 38% 20%
*Anthropogenic is primarily FF (except for NH3 where it includes domesticated animals, humans), also includes small contributions from fertilizer (NOx, NH3) and aircraft (SOx, NOx)
0
5
10
15
20
25
30
OC EC SOx NOx NH3 Dust/10
Tg
/yr
Natural
BB
BF
Anthropogenic
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CLIMATOLOGICAL DIRECT EMISSIONS FROM NORTH AMERICA
% ofGlobal
Emissions 8% 8% 20% 22% 9% 1%
*Anthropogenic is primarily FF (except for NH3 where it includes domesticated animals, humans), also includes small contributions from fertilizer (NOx, NH3) and aircraft (SOx, NOx)
0
2
4
6
8
10
12
14
16
OC EC SOx NOx NH3 Dust/10
Tg
/yr
Natural
BB
BF
Anthropogenic
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ACE-ASIA OC: IMPLICATIONS FOR TRANSPACIFIC TRANSPORT AND RADIATIVE FORCING
NORTHAMERICA
ASIA
High concentrations of OCaerosols measured in the FT
over Asia (not captured by models)[Heald et al., 2005a]
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
4 ug/sm3 (ACE-Asia) @ 50% RHTOA Radiative Forcing = -1.2 W/m2
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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
[Heald et al., 2005a]
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WET DEPOSITION IN GEOS-CHEM[Liu et al., 2001]
1. CONVECTIVE UPDRAFTS
Fraction lost during ascent dzScavenging efficiency () = 4x10-4 m-1
fscav=1-e-z
40% scavenged in 1 km
dz
2. RAINOUT
3. WASHOUT
Depends on fraction of grid square experiencing precipitation
(global avg = 2.5% stratiform, 0.4% convective)
Washout rate constant = 0.1 per mm precipapplied to max fraction of grid square
experiencing precipitation above.
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BIOGENIC SOA
Class Biogenic Hydrocarbons % contribution to SOA
Emissions from Asia (Tg/yr)
ALPHA -pinene, -pinene, sabinene, carene
45 22.2
LIMO Limonene 21 6.6
TERO -terpinene, -terpinenen, terpinolene
1 0.9
ALCO Myrcene, terpenoid alcohols, ocimene
11 8.8
SESQ Sesquiterpenes 22 3.4