1. Organic Carbon Aerosol: Insight from recent aircraft field campaigns
Colette L. Heald
NOAA Climate and Global Change Postdoctoral Fellow
Department of Civil and Environmental Engineering, Stanford University
October 27, 2006

2. AEROSOL IMPACTS ON AIR QUALITY
AIR QUALITY / HEALTH
VISIBILITY
Particulates contribute to urban smog:
Clear Day LA
April 16, 2001
Visibility reduction at Glen Canyon, Arizona
due to transpacific transport of Asian dust
[Environmental Working Group Report, 2005]

3. AEROSOL IMPACTS ON CLIMATE
DIRECT EFFECT
INDIRECT EFFECT
Scattering Radiation = COOLING
Absorbing Radiation = WARMING
Reflection
Refraction
Increase cloud albedo = COOLING
Increase cloud lifetime = COOLING
Absorption

4. ESTIMATED RADIATIVE FORCING OF CLIMATE
[IPCC, 2001]
Biogenic OC currently not included in forcing estimates  is it important?

5. ORGANIC CARBON AEROSOL
*Numbers from IPCC [2001]
Secondary Organic
Aerosol (SOA): 8-40 TgC/yr
Reactive
Organic
Gases
Nucleation or Condensation OC
Oxidation
by OH, O3, NO3
Monoterpenes
Fossil Fuel: TgC/yr
Biomass Burning: TgC/yr
Aromatics
Isoprene
Direct
Emission
Fossil Fuel Biomass
Burning
BIOGENIC SOURCES
ANTHROPOGENIC SOURCES

6. OBSERVING TROPOSPHERIC COMPOSITION ON ALL SCALES
SURFACE SITES
AIRCRAFT CAMPAIGNS
SATELLITES
Chemical characterization
throughout the
troposphere
Continuous,
global
measurements
Long-term monitoring
at the surface
AIR QUALITY
CLIMATE

7. ORGANIC CARBON AEROSOL: AT THE SURFACE
2004 NARSTO Assessment
Organic carbon constitutes 10-70% of aerosol mass at surface.
Difficult to distinguish primary from secondary contributions.

8. Single particles over NA
FIRST SUGGESTIONS OF HIGH ORGANIC CARBON AEROSOL CONCENTRATIONS IN THE FREE TROPOSPHERE
High organic loading
in the UT
High organic
loading
in the FT
Single particles over NA
[Murphy et al., Science, 1998]
TARFOX (E US)
[Novakov et al., JGR, 1998]

9. ACE-ASIA: FIRST OC AEROSOL MEASUREMENTS IN THE FREE TROPOSPHERE
(ACE-Asia aircraft campaign conducted off of Japan during April/May 2001)
[Mader et al., 2002]
[Huebert et al., 2003]
[Maria et al., 2003]
Mean Observations
Mean Simulation
Observations +
GEOS-Chem:
Global Chemical
Transport model
Concentrations of OC in the FT were under-predicted by a factor of !
[Heald et al., 2005]

10. CONTRAST: OTHER AEROSOLS IN ASIAN OUTFLOW
Sulfate
Elemental Carbon
Secondary
production
Scavenging
Scavenging
Mean Observations
Mean Simulation (GEOS-Chem)
Model simulates both the magnitude and profile of sulfate and
elemental carbon during ACE-Asia

11. ANY INDICATION THAT DIRECT EMISSIONS ARE UNDERESTIMATED?
Biomass Burning:
Satellite firecounts show no active fires in Siberia
Agricultural fires in SE Asia do not contribute in the FT.
Pollution:
There is a free tropospheric background of 1-4 μg sm-3 that is not correlated with CO or sulfate.
No indication of a primary source for OC in FT

12. SECONDARY ORGANIC AEROSOL
SOA parameterization [Chung and Seinfeld, 2002]
VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j
Parameters (a’s K’s) from smog chamber studies
Ai,j
Gi,j
Pi,j
Equilibrium (Komi,j)
 also f(POA)
Condensation of
low vapour pressure
ROGs on pre-
existing aerosol
Reactive
Organic Gases
Oxidation by
OH, O3, NO3
Simulated April Biogenic SOA
Biogenic VOCs
(eg. monoterpenes)
FT observations ~ 4mg/m3
Simulated SOA
far too small!

13. IMPLICATIONS FOR TRANSPACIFIC TRANSPORT
High concentrations of OC
aerosols measured in the FT
over Asia (not captured by models)
[Heald et al., 2005]
Observed
Simulated
Asian air masses
Sulfate: 0.24 µgm-3
OC: 0.53 µgm-3
Twice as much OC
aerosol as sulfate
observed at Crater Lake
[Jaffe et al., 2005]
ASIA
NORTH
AMERICA
PACIFIC

14. SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA
[Volkamer et al., 2006]
Global underestimate in SOA?

15. ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH ATLANTIC IN SUMMER 2004
Multi-agency,
International Collaboration
2004 fire season in North America:
worst fire season on record in Alaska
MOPITT Observations of CO Transport
(July 17-19) [Turquety et al., submitted]
Emissions derived from MODIS
hot spots [Turquety et al., submitted]
OC: 1.4 TgC
OC emissions from biomass burning were 4 times climatological average!

16. WHAT CONTRIBUTES TO OC AEROSOL OVER NORTH AMERICA?
Observed boreal fire
Influence down-wind
Simulated source attribution
for “background” OC
NOAA WP-3 Flight tracks
BB filtered
using CH3CN
*includes isoprene as a source of SOA [Kroll et al., 2005]
OC concentrations in the free troposphere doubled as a result of Alaskan boreal fires. Is model attribution of remaining OC sources correct?

17. DO WE UNDERSTAND OC AEROSOL OVER NORTH AMERICA?
Sulfur Oxides (SOx)
Water soluble OC Aerosol (WSOC)
Observed
Simulated
OC aerosol concentrations 3x
lower than observed off of Asia
OC aerosol concentrations captured by the model, BUT we cannot simulate variability in observations (R=0.21)  incomplete understanding of formation.
[Heald et al., accepted]
Note: biomass burning plumes were removed

18. WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION?
Cloud
Processing
1. Production more
efficient at low NOx
2. Multi-step oxidation
SOA: ?? TgC/yr
New formation pathways
Nucleation or Condensation OC
ROG
Heterogeneous Reactions
Additional
Precursors
Oxidation
by OH, O3, NO3
FF: TgC/yr
BB: TgC/yr
Isoprene
Monoterpenes
Aromatics
Direct
Emission
Fossil Fuel Biomass
Burning
BIOGENIC SOURCES
ANTHROPOGENIC SOURCES

19. 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)

20. CARBON CYCLE AND POTENTIAL RADIATIVE IMPLICATIONS
4 μg/m3 (ACE-Asia)
50% RH: 0.057
TOA Radiative Forcing = -1.2 W/m2
OC AEROSOL
1 µg/m3 in the FT globally ~ 100 TgC/yr
VOC EMISSIONS
TgC/yr
[IPCC, 2001]
DISSOLVED
ORGANIC CARBON
IN RAINWATER
430 TgC/yr
[Wiley et al., 2000]

21. CURRENT WORK: HOW WILL SOA FORMATION RESPOND TO A FUTURE CLIMATE?
Using a coupled
land-atmosphere model
(NCAR CCSM)
Oxidant levels:
Effected by hydrological cycle and anthropogenic pollution levels
Biogenic Emissions
of precursors:
T/light/moisture
Precipitation:
Enhanced removal
Anthropogenic Emissions:
Increasing aromatic emissions
More surface area for aerosol condensation
Land Use Change

22. ACKNOWLEDGEMENTS
Daniel Jacob, Rokjin Park, Solène Turquety, Rynda Hudman
Barry Huebert
Lynn Russell
John Seinfeld,
Hong Liao
Rodney Weber,
Amy Sullivan
Rick Peltier
ITCT-2K4 Science Team
Hosts: Inez Fung &
Allen Goldstein