Investigating Organic Aerosol Loading in the Remote Marine Environment Kateryna Lapina 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-Chem Maritime Aerosol Network provides AOD measurements from various ships of opportunity (2004 – current) 2007 AOD < 0.4 GEOS-Chem: v with sea salt from Jaeglé et al What is the source of this bias? 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 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 Based on Langmann et al Marine OM emissions total 8 – 9TgC OM = A x [Chl]%OM = x [Chl] + 10 OM = f([Chl], wind speed, SST) 8.2 TgC 8.9 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