Investigating Organic Aerosol Loading in the Remote Marine Environment

Kateryna Lapina klapina@atmos.colostate.edu

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 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-ChemMaritime Aerosol Network provides AOD measurements from various ships of opportunity (2004 – current)

2007AOD < 0.4

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

What is the source of this bias?

http://aeronet.gsfc.nasa.gov/new_web/maritime_aerosol_network.html

MODIS vs MAN GEOS-Chem vs MAN

Measurements of Aerosol Composition

Aerodyne Aerosol Mass Spectrometer (AMS) [Jayne et al., 2000; DeCarlo et 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

Sulfate: generally unbiased Sea salt cannot account for low model bias in AOD

- Obs- GEOS-Chem

AOD: GC minus MODIS GC Sea salt AOD

Sea salt?

Sulfate?

Anti-correlated

Marine Organic Matter (OM)

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]

From O’Dowd et al. 2004, Nature

Mas

s fra

ction

(%)

Mas

s m

ass (

ug/m

-3)

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

High biological activity

Chlorophyll concentrations [mg m-3]

Mace Head

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

Marine OM emissions total 8 – 9TgC

OM = A x [Chl] %OM = 49.129 x [Chl] + 10OM = f([Chl], wind speed, SST)

8.2 TgC8.9 TgC

Aerosol Composition: Model vs Observations OM

Large underestimation when marine OM not included

Obs

GC standard

GC_Spracklen08

GC_Langmann08

GC standard OM GC_Spracklen08 OM

OM obs

Conclusions

• The GEOS-Chem model underestimates observed surface OM when no marine OM source is included.

• Marine OM source of <9 TgC yr-1 is 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