Global transport and radiative forcing of biomass burning aerosols

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Global transport and radiative forcing of biomass
burning aerosols

• Yang Chen, Qinbin Li, Ralph Kahn
• Jet Propulsion Laboratory
• California Institute of Technology, Pasadena
• Evan Lyons, James Randerson
• University of California, Irvine

The 3rd GEOSChem Users' Meeting Harvard
University, April 12, 2007
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Objectives and outline

• Large uncertainties in the estimation of aerosol
  radiative forcing.
• -0.1-0.9 W/m2 for direct forcing (IPCC,2007).
• -0.3-1.8 W/m2 for indirect forcing.
• Purpose Combine satellite observations and
  chemical transport models to further constrain
  quantification of aerosol (particularly the
  biomass burning aerosols) radiative forcing.
• First step Estimate the global aerosol direct
  radiative effect using Multi-angle Imaging
  SpectroRadiometer (MISR) observations.
• Better aerosol retrievals over land.
• First attempt at estimating aerosol direct
  radiative effect on a global basis (over both
  ocean and land) using satellite observation based
  approach.
• Ongoing modeling study GEOS-Chem simulations of
  aerosols using different GFEDv2 biomass burning
  emissions.
• Diurnal cycles
• Synoptic variation
• Injection height

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Introduction to MISR

• Multi-angle multi-channel spectroradiometer on
  board satellite TERRA
• Global Mode
• 275 m sampling resolution for nadir camera and
  red band of other cameras
• 1.1 km for the other channels
• 400-km swath
• Global coverage 9 days at equator, 2 days at
  poles
• Continuous data retrieval since Feb 2000.
• Major products used
• TOA albedo (2.2x2.2 km2)
• AOD (17.6x17.6 km2)
• Cloud mask (1.1x1.1 km2)
• BHRPAR (1.1x1.1 km2)
• All products are re-sampled to 17.6x17.6 km2 for
  this study

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Method
MISR observations
Nadir view
Cloud mask
TOA Broadband Albedo (with aerosol)
Aerosol Optical Depth
Albedo AOD regression
AOD
TOA albedo
Cloud mask
BHRPAR
1x 1 grid
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Global distribution of AOD, albedo, and BHRPAR
(July, 2002)
26 BHRPAR bins 00.1 each 0.01 interval
0.10.4 each 0.02 interval Above 0.4 1 level
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AlbedoAOD correlation over ocean
AlbedoAOD correlation for 10x5 grids. The
slopes indicate the ability of aerosols to affect
TOA radiative flux.
Alternative method do global regression for each
solar zenith angle.
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AlbedoAOD correlation over land
AlbedoAOD correlation for 10x5 grids
A
C
A East US
B
B Central Africa
Global correlation
C Saharan desert
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Aerosol direct radiative effect
(a)
(b)
(a) Clear-sky and (b) all-sky aerosol direct
radiative effect (W/m2) for July 2002.
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Aerosol direct radiative effect
From this study (July, 2002)
Direct ARE (Clear sky) (W/m2) Direct ARE (All sky) (W/m2)
Global -4.70 -1.49
Over ocean -4.54 -1.95
Over land -4.88 -1.18
From previous satellite-based studies
Source Direct ARE (W/m2) Spatial coverage Temporal coverage Satellite data source
Zhang and Christopher, 2005 -6.4 2.6 Cloud-free oceans 09/2000-08/2001 CERES, MODIS
Christopher and Zhang, 2002 -6 Cloud-free oceans 09/2000 CERES, MODIS
Loeb and Kato, 2002 -4.6 1 Cloud-free tropical oceans 01/1998-08/1998, 03/2000 CERES, TRMM VIRS
Loeb and Manalo-Smith, 2005 -5.5, -3.8 Cloud-free oceans 03/2000-12/2003 CERES, MODIS
Loeb and Manalo-Smith, 2005 -2.0, -1.6 All-sky oceans 03/2000-12/2003 CERES, MODIS
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Uncertainties

• Satellite retrieval of aerosol, albedo and
  surface properties.
• Cloud contamination.
• Diurnal variability.
• TOA albedo narrow-to-broadband conversion.
• Surface heterogeneity.

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Diurnal cycle effect on GEOS-Chem aerosol
simulation
Ongoing modeling study

• Simulation conditions
• Model GEOS-Chem v7-03-06
• Meteorology GEOS-4
• Simulation type Offline aerosol simulation
• Simulation period 06/2004 08/2004
• Biomass burning emissions Global Fire Emissions
  Database version 2 (GFEDv2) with 8 day time
  interval
• with diurnal cycle
• without diurnal cycle

07/2004
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Diurnal cycle effect on Central Africa
Ongoing modeling study
C emissions
Local noon
BCPI concentration difference(with diurnal cycle
- without)
With diurnal cycle, major emissions occur when
the PBL is high. The vertical mixing causes
faster dilution and the dissipation of
pollutants. The accumulation of aerosols during
local night is weaker.
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Diurnal cycle effect on Alaska and Northern Canada
Ongoing modeling study
Emissions from source
C emissions
Local noon
BCPI concentration difference(with diurnal cycle
- without)
BCPI concentration in nearby grid
When the biomass burning emission is very strong
and PBL is low, the dissipation effect is weaker.
For some regions near the strong source, the
transport is more important than the local
emission.
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Conclusions and future work

• Conclusions
• By using MISR datasets, first satellite-based
  attempt to estimate global aerosol direct
  radiative effect over both ocean and land has
  been made.
• Aerosols have different impacts on TOA albedo in
  different regions due to different aerosol
  properties and surface types.
• Global mean result of aerosol radiative effect
  over ocean is well in the range of other studies
  in literature.
• By including diurnal cycle of biomass burning
  emissions in GEOS-Chem simulation, aerosol
  concentrations at surface may increase or
  decrease, depending on the source type and
  intensity, the boundary layer height, and the
  relative importance of transport and local
  emissions.
• Future work
• Extend the satellite-based estimation of aerosol
  direct radiative effect to include seasonal and
  inter-annual variability.
• Study how synoptic variability of biomass burning
  emissions and the inclusion of smoke injection
  height will affect the global distribution of
  aerosols, and the implication to the aerosol
  radiative forcing.

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Acknowledgment

• MISR data were obtained from the NASA Langley
  Atmospheric Sciences Data Center
  (http//eosweb.larc.nasa.gov/).
• We used Global Fire Emissions Database version2
  (van der Werf et al.,2006) resampled to an 8day
  time step using MODIS fire hot spots (Giglio et
  al., 2003).
• GEOS-Chem model is managed by the Atmospheric
  Chemistry Modeling Group at Harvard University.

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