secondary organic aerosols: what we know and current cam treatment
DESCRIPTION
Secondary Organic Aerosols: What we know and current CAM treatment. Colette L. Heald ([email protected]). Chemistry-Climate Working Group Meeting, CCSM March 22, 2006. ORGANIC CARBON AEROSOL. *Numbers from IPCC [2001]. Secondary Organic Aerosol (SOA): 8-40 TgC/yr. Reactive - PowerPoint PPT PresentationTRANSCRIPT
Secondary Organic Aerosols:What we know and current CAM treatment
Chemistry-Climate Working Group Meeting, CCSMMarch 22, 2006
Colette L. Heald([email protected])
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]
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
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
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?
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)
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)
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.
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
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
SOx CONCENTRATIONS: IMPROVE SITES (1988-2004)
Sulfate concentrations
in the US overestimated
with Mozart wetdep
Mozart wetdep CAM wetdep
SO2
SO4
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)
OC CONCENTRATIONS: IMPROVE SITES (1988-2004)
Mozart wetdep CAM wetdep
OC comparison with observations over the US not definitive…
AEROSOL OPTICAL DEPTH COMPARISON (2001/2005)
Less wet deposition in Mozart increases AOD better match with satellitesover water, but overestimate over land
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.
SEASONAL CYCLE: AOD COMPARISONSLAND OCEAN
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)
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
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
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
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]
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
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)
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
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
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
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]
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.
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