Transcript Transpacific transport of anthropogenic aerosols and

Organic Carbon Aerosol:
Insight from recent aircraft field campaigns
Colette L. Heald
NOAA Climate and Global Change Postdoctoral Fellow
([email protected])
Department of Civil and Environmental Engineering, Stanford University
October 27, 2006
AEROSOL IMPACTS ON AIR QUALITY
AIR QUALITY / HEALTH
VISIBILITY
Particulates contribute to urban smog:
LA
Clear Day
April 16, 2001
Visibility reduction at Glen Canyon, Arizona
due to transpacific transport of Asian dust
AEROSOL IMPACTS ON CLIMATE
DIRECT EFFECT
INDIRECT EFFECT
1. Scattering Radiation = COOLING
Reflection
Refraction
Increase cloud albedo = COOLING
Increase cloud lifetime = COOLING
2. Absorbing Radiation = WARMING
Absorption
ESTIMATED RADIATIVE FORCING OF CLIMATE
[IPCC, 2001]
Biogenic OC currently not included in forcing estimates  is it important?
ORGANIC CARBON AEROSOL
*Numbers from IPCC [2001]
Reactive
Organic
Gases
Secondary Organic
Aerosol (SOA): 8-40 TgC/yr
Nucleation or Condensation
OC
Oxidation
by OH, O3, NO3
Isoprene
Monoterpenes
Aromatics
Fossil Fuel: 10-30 TgC/yr
Biomass Burning: 45-80 TgC/yr
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
OBSERVING TROPOSPHERIC COMPOSITION
ON ALL SCALES
SURFACE SITES
Long-term monitoring
at the surface
AIR QUALITY
AIRCRAFT CAMPAIGNS
Chemical characterization
throughout the
troposphere
CLIMATE
SATELLITES
Continuous,
global
measurements
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.
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]
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]
Mean Observations
Mean Simulation
Observations
[Maria et al., 2003]
GEOS-Chem:
Global Chemical
Transport model
Concentrations of OC in the FT were under-predicted by a factor of 10-100!
[Heald et al., 2005]
CONTRAST: OTHER AEROSOLS IN ASIAN OUTFLOW
Sulfate
Secondary
production
Scavenging
Elemental Carbon
Scavenging
Mean Observations
Mean Simulation (GEOS-Chem)
Model simulates both the magnitude and profile of sulfate and
elemental carbon during ACE-Asia
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
SECONDARY ORGANIC AEROSOL
Secondary
Organic Aerosol
Condensation of
low vapour pressure
ROGs on preexisting aerosol
Reactive
Organic Gases
Oxidation by
OH, O3, NO3
SOA parameterization [Chung and Seinfeld, 2002]
VOCi + OXIDANTj  ai,jP1i,j + ai,jP2i,j
Gi,j
Equilibrium (Komi,j)
 also f(POA)
Pi,j
Ai,j
Parameters (a’s K’s) from smog chamber studies
Simulated April Biogenic SOA
Biogenic VOCs
(eg. monoterpenes)
FT observations ~ 4mg/m3
Simulated SOA
far too small!
IMPLICATIONS FOR TRANSPACIFIC TRANSPORT
Observed
Simulated
Asian air masses
Sulfate: 0.24 µgm-3
OC: 0.53 µgm-3
ASIA
High concentrations of OC
aerosols measured in the FT
over Asia (not captured by models)
[Heald et al., 2005]
PACIFIC
NORTH
AMERICA
Twice as much OC
aerosol as sulfate
observed at Crater Lake
[Jaffe et al., 2005]
SEVERAL STUDIES SUGGESTING UNDERESTIMATE OF SOA
[Volkamer et al., 2006]
Global underestimate in SOA?
ICARTT: COORDINATED ATMOSPHERIC CHEMISTRY
CAMPAIGN OVER EASTERN NORTH AMERICA AND NORTH
ATLANTIC IN SUMMER 2004
Multi-agency,
International Collaboration
MOPITT Observations of CO Transport
(July 17-19) [Turquety et al., submitted]
2004 fire season in North America:
• worst fire season on record
in Alaska
Emissions derived from MODIS
hot spots [Turquety et al., submitted]
OC: 1.4 TgC
OC emissions from biomass burning were 4 times climatological average!
WHAT CONTRIBUTES TO OC AEROSOL OVER
NORTH AMERICA?
NOAA WP-3 Flight tracks
Observed boreal fire
Influence down-wind
Simulated source attribution
for “background” OC
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?
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.
Note: biomass burning plumes were removed
[Heald et al., accepted]
WHAT DON’T WE UNDERSTAND ABOUT SOA FORMATION?
Cloud
Processing
1. Production more
efficient at low NOx
2. Multi-step oxidation
ROG
Additional
Precursors
SOA: ?? TgC/yr
New formation pathways
Nucleation or Condensation
OC
Heterogeneous Reactions
Oxidation
by OH, O3, NO3
Isoprene Monoterpenes
FF: 45-80 TgC/yr
BB: 10-30 TgC/yr
Aromatics
Direct
Emission
Fossil Fuel
BIOGENIC SOURCES
Biomass
Burning
ANTHROPOGENIC SOURCES
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)
CARBON CYCLE AND POTENTIAL RADIATIVE
IMPLICATIONS
4 μg/m3 (ACE-Asia)
AOD @ 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
500-1000 TgC/yr
[IPCC, 2001]
DISSOLVED
ORGANIC CARBON
IN RAINWATER
430 TgC/yr
[Wiley et al., 2000]
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
Land Use Change
Precipitation:
Enhanced removal
Anthropogenic Emissions:
Increasing aromatic emissions
More surface area for aerosol condensation
ACKNOWLEDGEMENTS
Daniel Jacob, Rokjin Park, Solène Turquety, Rynda Hudman
Lynn Russell
Rodney Weber,
Amy Sullivan
Rick Peltier
Barry Huebert
John Seinfeld,
Hong Liao
ITCT-2K4 Science Team
Hosts: Inez Fung &
Allen Goldstein