Organic Carbon Aerosol in the Free Troposphere:Insights from ACE-Asia and ICARTT

Fall AGUDecember 8, 2005

Colette L. Heald, 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

Acknowledgements: NOAA-OGP, EPA-STAR, NSF-ATM

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]

Global Model Representation of SOA:1. “Effective primary” yield2. Two-product empirical fit to smog chamber data

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 [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.

Seinfeld group Huebert group Russell group

(ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)

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]

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.

SOA

WSOMC

OMC (=POA+SOA)

OMC=organic molecular carbon (=1.4xOC)WS=water soluble (40-80% of total OC, primarily SOA)

EMISSIONS OF OC FROM BOREAL FIRES IN ALASKA/YUKONFires 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) making these emissions a dominant source of OC in the FT.

Injection of BB emissions into the FT increases the OC observed in the FT down-wind. However lack of correlation with CO in observations suggests

that not all the OC can be attributed to the BB source.

ITCT 2K4 OMC

Observations (WS only)GEOS-Chem Simulation (with injected emiss)GEOS-Chem Simulation (with emission in BL)

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

ISOPRENE SOA SOURCE: COMPARISON WITH OBSERVATIONS

GEOS-Chem: 2-product SOA model

IMPROVE (July-August 2004)

GEOS-Chem: 10%terp+3%isop

GEOS-Chem: 10%terp

POA: 0.73SOA: 0.45

POA: 0.73SOA: 0.75

Isoprene SOA sources improves agreement with IMPROVE surface observations (improves spatial correlation) particularly in the East

Observations (WS only)GEOS-Chem (2-product SOA)GEOS-Chem (10% terp SOA)GEOS-Chem (10%terp + 3%isop SOA)

POA: 0.73SOA: 1.16

ITCT-2K4 OMC

CLUES FROM CORRELATIONS WITH OTHER ICARTT SPECIES?

BL (< 2km)FT (> 2km)

Cloud-processing?[Lim et al., 2005]

Weak correlation with biogenic tracer in the FT

No correlation witharomatic SOAprecursor

Weak correlationwith pollution

In the FT

No correlation withphotochemically-

produced O3

In the FT

No correlationwith product of

isoprene oxidation(Kroll et al. suggest

MACR forms SOA)

Note: BB plumes removed

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)

Chemistry leading to SOA production is not well understood! (And not represented in global models)

BUT field observations can provide insights.

Conclusions:1. The large underestimate in OC aerosol concentrations observed during

ACE-Asia cannot be explained by an underestimate in primary emissions

2. High OC concentrations in the FT observed during ICARTT can be partially explained by injection of aerosols from boreal fires in Alaska.

3. Including direct production of SOA from isoprene improves the correlation with surface observations during ICARTT.

4. OC concentrations in the FT are sensitive to efficiency of wet loss processes. How internally mixed are OC aerosols?

5. Many, many processes are not included in global models (SOA formation in clouds, polymerization reactions, heterogeneous reactions, etc.). To what degree can models represent OC aerosol concentrations (and the important biosphere-atmosphere feedbacks) using simple parameterizations?

ORGANIC CARBON IN THE FT: AN ONGOING QUESTION