#06 Climate impacts of marine organic aerosols

Abstract

Clouds in remote marine areas are primarily influenced by natural aerosol sources (Hamilton et al., PNAS, 2014), and the ability to constrain climate sensitivity using historical climate records is in part limited by quantification of remote aerosol concentrations (Karydis et al., 2012; Carslaw et al., Nature, 2013).  It has long been noted that organic matter can make up a substantial portion of submicron marine aerosol mass (Hoffman and Duce, 1977), but the emissions of organic matter in sea spray have not been included into the majority of climate models, and previous representations of these emissions have relied on satellite-observed chlorophyll, which has known limitations as a proxy for sea spray organic matter emissions. A new representation of marine primary organic aerosol emissions in sea spray aerosol (Burrows et al., 2014) has been implemented in ACME.  The new treatment represents an important step towards linking ocean biogeochemistry process models with the surface chemistry that determines sea spray aerosol formation.  This poster presents the results of an initial evaluation of the impacts of this new emission source on model aerosols, clouds and climate within the ACME v0 model.  A control simulation with no marine organic aerosol (standard model) is compared with simulations that include the new marine organic aerosol treatment.  Impacts will be examined on fields including aerosol burden, CCN number, cloud droplet number, cloud thickness and amount, cloud shortwave forcing, and total reflected shortwave radiation.  A recent study of satellite-observed cloud properties, to which members of this team contributed (McCoy et al., 2015), found that marine organic aerosol may measurably elevate the mean cloud shortwave forcing over the Southern Ocean via the cloud albedo effect.  Preliminary evaluation of the new parameterization indicates that the sensitivity of modeled clouds to the new aerosol source is roughly in agreement with the sensitivity inferred via top-down constraints by McCoy et al., 2015.

References:

Burrows, S.M., Ogunro, O., Frossard, A.A., Russell, L.M., Rasch, P.J. and Elliott, S.M., 2014. A physically based framework for modeling the organic fractionation of sea spray aerosol from bubble film Langmuir equilibria.Atmos. Chem. Phys, 14(24), pp.13-601.

Carslaw, K.S., Lee, L.A., Reddington, C.L., Pringle, K.J., Rap, A., Forster, P.M., Mann, G.W., Spracklen, D.V., Woodhouse, M.T., Regayre, L.A. and Pierce, J.R., 2013. Large contribution of natural aerosols to uncertainty in indirect forcing. Nature, 503(7474), pp.67-71.

Hamilton, D.S., Lee, L.A., Pringle, K.J., Reddington, C.L., Spracklen, D.V. and Carslaw, K.S., 2014. Occurrence of pristine aerosol environments on a polluted planet. Proceedings of the National Academy of Sciences, 111(52), pp.18466-18471.

Hoffman, E.J. and Duce, R.A., 1977. Organic carbon in marine atmospheric particulate matter: Concentration and particle size distribution. Geophysical Research Letters, 4(10), pp.449-452.

Karydis, V.A., Capps, S.L., Russell, A.G. and Nenes, A., 2012. Adjoint sensitivity of global cloud droplet number to aerosol and dynamical parameters. Atmospheric Chemistry and Physics, 12(19), pp.9041-9055.

McCoy, D.T., Burrows, S.M., Wood, R., Grosvenor, D.P., Elliott, S.M., Ma, P.L., Rasch, P.J. and Hartmann, D.L., 2015. Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo. Science advances, 1(6), p.e1500157.