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Investigating Organic Aerosol Loading in the Remote Marine Environment

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Investigating Organic Aerosol Loading in the Remote Marine Environment. Kateryna Lapina

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Investigating Organic Aerosol Loading in the Remote Marine Environment


Colette Heald, Dominick Spracklen, Steve Arnold, James Allan, Hugh Coe, Gordon McFiggans, Soeren Zorn, Frank Drewnick, Tim Bates, Lelia Hawkins, Lynn Russell, Sasha Smirnov, Colin O’Dowd and Andy Hind

Acknowledgments: SeaWIFS and MODIS teams

marine aod modis vs geos chem
Marine AOD: MODIS vs GEOS-Chem

From Jaeglé et al. 2011, ACP

  • New sea salt source function improves agreement of coarse AOD with MODIS
  • Remaining low GEOS-Chem bias: due to fine mode
marine aod man vs geos chem
Marine AOD: MAN vs GEOS-Chem
  • Maritime Aerosol Network
  • provides AOD measurements from various ships of opportunity (2004 – current)



AOD < 0.4


v8-03-01 with sea salt from Jaeglé et al. 2011

What is the source of this bias?

measurements of aerosol composition
Measurements of Aerosol Composition
  • Aerodyne Aerosol Mass Spectrometer (AMS) [Jayne et al., 2000; DeCarloet al., 2006; Canagaratna et al., 2007]:
  • real-time
  • sulfate, OM, nitrate & ammonium
  • fine mode
  • Ship-based measurements during 2006 – 2008
  • Fresh pollution excluded from analysis
possible sources of fine aod bias
Possible Sources of Fine AOD Bias


Sea salt?

AOD: GC minus MODIS GC Sea salt AOD



  • Obs
  • GEOS-Chem
  • Sulfate: generally unbiased
  • Sea salt cannot account for low model bias in AOD
marine organic matter om
Marine Organic Matter (OM)

From O’Dowd et al. 2004, Nature

Mass fraction (%)

High biological activity

Mass mass (ug/m-3)

Mace Head

Chlorophyll concentrations [mg m-3]

  • Currently not included in GEOS-Chem
  • Wide range of emissions estimates: 2.3 to 75 TgC yr-1
  • [Spracklen et al., 2008; Roelofs, 2008; Langmann et al., 2008; Gantt et al., 2009; Ito and Kawamiya, 2010; Myriokefalitakis et al., 2010; Long et al., 2011; Vignati et al., 2010]

Could marine OM be the reason for low AOD bias in GEOS-Chem?

modeling of sub micron marine om
Modeling of Sub-micron Marine OM

[Chl] as a proxy for bioproductivity[O'Dowd et al., 2004; Yoon et al., 2007]

Based on Spracklen et al. 2008

Based on Langmann et al. 2008

OM = A x [Chl]

%OM = 49.129 x [Chl] + 10

OM = f([Chl], wind speed, SST)

8.9 TgC

8.2 TgC

Marine OM emissions total 8 – 9TgC

aerosol composition model vs observations
Aerosol Composition: Model vs Observations

GC standard OM GC_Spracklen08 OM


  • Obs
  • GC standard
  • GC_Spracklen08
  • GC_Langmann08

OM obs

Large underestimation when marine OM not included

  • The GEOS-Chem model underestimates observed surface OM when no marine OM source is included.
  • Marine OM source of <9 TgCyr-1is sufficient to account for observed marine OM concentrations.
  • The schemes developed based on satellite-derived chlorophyll-a concentrations do not adequately describe the variability in observed OM.
  • Marine OM makes a very small contribution to total marine AOD (~0.003).

Lapina et al. 2011, ACPD