Secondary Organic Aerosols:What we know and current CAM treatment

Chemistry-Climate Working Group Meeting, CCSMMarch 22, 2006

Colette L. Heald(heald@atmos.berkeley.edu)

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