using satellite observations to investigate natural aerosol loading colette l. heald david a....
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Using satellite observations to investigate natural aerosol loading
Colette L. HealdDavid A. Ridley, Kateryna Lapina
UPMC ParisMarch 22, 2011
DUST FROM NORTH AFRICA: IMPACTING AQ AND THE BIOSPHERE DOWN-WIND
More than half of dust emitted globally from N. Africa
TOMS: June 13-21, 2001
summer
winter/spring
Miami (1989-1997)
[Prospero et al., 1999]
[Prospero et al., 1981]
French Guiana (1978-1979)
SATELLITE CONSTRAINTS ON DUST SOURCE & TRANSPORT
Dave RidleyGEOS-Chem overestimates observed AOD in source region, underestimates summertime export
REALISTIC APPORTIONMENT OF SUB-MICRON DUST MASS
Shifted mass to larger sub-micron sizes (less optically efficient). Reduces AOD in better agreement with satellite & AERONET observations
[Haywood et al., 2003]
Observed Saharan dust size distribution
Simulated decrease in AOD
OLDNEW
DUST TRANSPORT FROM NORTH AFRICA
CALIOP GEOS-Chem CALIOP GEOS-ChemWINTER SUMMER
Annual Mean AOD
Good model simulation of dust transport and removal in winter/spring. Underestimate in dust in the SAL in summertime.
DEPOSITION OF AFRICAN DUST & PHOSPHOROUS IN THE AMAZON
We estimate 13 Tg/yr transported to Amazon annually. This is ~10-25% of the P supply for the Amazon. Otherwise from fires and biogenic particles [Mahowald et al., 2005].
Impact of greening of the Sahel on productivity of the Amazon?
[Ridley et al., in prep]
ANNUAL
ANNUAL MEAN AOD OVER THE REMOTE OCEANS
MODIS GEOS-Chem
% Difference GEOS-Chem Sea Salt
GEOS-Chem underestimates (~30%) marine AOD observed by MODIS . Likely fine aerosol [Jaegle et al., 2010], but does not match simulated sea salt.
Gong [2003] sea salt scheme updated to include SST dependence & validated against observations [Jaeglé et al., 2010]
Kateryna Lapina
COMPARISON WITH MARTIME AEROSOL NETWORK (MAN)
Model AOD (over remote regions) is also ~13% low compared to MAN
OTHER POSSIBLE FINE MARINE PARTICLE SOURCES
[O’Dowd et al., 2004]
GEOS-Chem simulation of sulfate relatively unbiased not the problem.BUT under biologically active conditions, OA dominates sub-micron aerosol mass.
SeaWIFS
Comparison of simulated sulfate to recent cruise observations (AMS) Observed aerosol composition
at Mace Head
IS THE OCEAN AN IMPORTANT SOURCE OF OA?Previous estimates range from 2.3 to 75 TgC/yr
No marine OA With marine OA
Observations from 5 ship cruises show that marine OA from 2 schemes
[Spracklen et al., 2008; Langmann et al., 2008] of ~8 TgC/yr are more than
sufficient to reproduce sub-micron OA.
Makes very little contribution to AOD (0.003).
[Lapina et al., ACPD, 2011]
OA Emissions
ORGANIC AEROSOL MAKES UP AN IMPORTANT FRACTION OF OBSERVED AEROSOL
Globally makes up 25-75% of total fine aerosol at the surface (ignoring soot here)
[Zhang et al., 2007]SulfateOrganics
CHALLENGES IN MODELING THE RIGHT LEVELS OF OA
SOA measured/modeled = 4-100!
[Volkamer et al., 2006]
Models do get it right sometimes (even more puzzling?) but is it for the right reason?
ITCT-2K4
IMPEXAMAZE-08
AMMA
Egbert
WHY DON’T MODELS GET IT RIGHT….
Terpenes(gas-phase)PBAP
Hydrocarbons(gas-phase & particulate)
Uncertain Formation (Missing sources? Poorly understood processes?)
Continuing Oxidation/Partitioning in the Atmosphere
10,000’s of (unidentified?) compounds with variable properties
CAN SATELLITE OBSERVATIONS SHED ANY LIGHT ON THE BUDGET OF OA?
SURFACE REFLECTANCE
Bottom-up calculations suggest that SOA source may be anywhere from 140-910 TgC/yr [Goldstein and Galbally, 2007].
topz
0
AOD= α RH z M z dz
Organicaerosol
Sulfate Dust
Sea SaltNitrate
SATELLITE AOD
Assumptions:Optical PropertiesSize Distributions
Aerosol Distributions
AEROSOL SPECIATED MASS CONCENTRATIONS
Soot
IF ONLY AEROSOL IN THE ATMOSPHERE WAS OA, WHAT LOADING IS IMPLIED BY SATELLITE AOD?
Calculate the “hypothetical” AOD implied by a constant 1 g/sm3 profile over the land, and see how we need to scale this locally to make up ENTIRE AOD reported by MISR.
Inverted OA loading is 3.5 TgC over land.Assume a 6 days lifetime = 215 TgC/yr
extrapolate to include outflow ~430 TgC/yr. (middle of Goldstein & Galbally range)
Inverted total MISR AOD: Surface OA concentrations
topz
0
AOD= α RH z M z dz
Estimate that ~150 TgC/yr source is required to close the
MISR-GEOS-Chem* discrepancy.
DJF JJA
MISR
GEOS-Chem*
MISR-GEOS-Chem*
*excluding OA
A MORE REALISTIC POSSIBILITY:REMOVE CONTRIBUTIONS FROM DUST, BC, INORGANICS
(assuming all the negative bias in the model is ONLY OA)
UNCERTAINTY ANALYSIS (boring but important!)
Assumed optical properties based on GADS database and log-normal size distribution recently
evaluated by Drury et al. [2010]
Uncertainty on estimated OA source = 80%
Estimated uncertainty on OA budget due to: Uncertainty on OA optical properties
* Except over high RH regions
Aerosol optical propertiesSize parametersRefractive indicesAerosol water uptake (growth factor)Relative humidity (assuming 5% uncertainty in GEOS-5 fields)
50%20%10%6%*
Conversion from burden to sourceAerosol lifetime (including effects of vertical profile and export fraction)
50%
Global budget of “other” aerosols simulated in GEOS-Chem
25%
MISR AOD measurements 10%
Total Error (added in quadrature) 80%
This is more than THREE TIMES what is currently included in global models….
BUT at the low end of Goldstein & Gallbally [2007] range.
HAVE WE REDUCED THE UNCERTAINTY ON THE OA BUDGET?
910
47 Existing GEOS-Chem sources
140 Our satellite top-down estimate 150
Range estimated
by: Goldstein
and Galbally [2007]
All units in TgCyr-1
[Heald et al., 2010]
Acknowledgments: Easan Drury, Sonia Kreidenweis, Dominick Spracklen, Steve Arnold, James Allan, Hugh Coe and Gordon
McFiggans, Soeren Zorn, Frank Drewnick, Tim Bates, Lelia Hawkins, Lynn Russell, Sasha Smirnov, Colin O’Dowd, Andy Hind and MISR,
MODIS & CALIOP retrieval teams