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| Titel |
A physically based framework for modeling the organic fractionation of sea spray aerosol from bubble film Langmuir equilibria |
| VerfasserIn |
S. M. Burrows, O. Ogunro, A. A. Frossard, L. M. Russell, P. J. Rasch, S. M. Elliott |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 24 ; Nr. 14, no. 24 (2014-12-19), S.13601-13629 |
| Datensatznummer |
250119256
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| Publikation (Nr.) |
 copernicus.org/acp-14-13601-2014.pdf |
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| Zusammenfassung |
The presence of a large fraction of organic matter in primary sea spray aerosol (SSA) can
strongly affect its cloud condensation nuclei activity and interactions with marine clouds.
Global climate models require new parameterizations of the SSA composition in order to improve the representation of these processes.
Existing proposals for such a parameterization use remotely sensed
chlorophyll a concentrations as a proxy for the biogenic
contribution to the aerosol. However, both observations and
theoretical considerations suggest that existing relationships with
chlorophyll a, derived from observations at only a few
locations, may not be representative for all ocean regions.
We introduce a novel framework for parameterizing the fractionation
of marine organic matter into SSA based on a competitive
Langmuir adsorption equilibrium at bubble surfaces. Marine organic
matter is partitioned into classes with differing molecular weights,
surface excesses, and Langmuir adsorption parameters. The classes
include a lipid-like mixture associated with labile dissolved organic carbon (DOC), a
polysaccharide-like mixture associated
primarily with semilabile DOC, a protein-like mixture with concentrations intermediate
between lipids and polysaccharides, a processed mixture associated with
recalcitrant surface DOC, and a deep abyssal humic-like mixture.
Box model calculations have been performed for several cases of
organic adsorption to illustrate the underlying concepts. We then
apply the framework to output from a global marine biogeochemistry
model, by partitioning total dissolved organic carbon into several
classes of macromolecules. Each class is represented by model
compounds with physical and chemical properties based on existing
laboratory data. This allows us to globally map the predicted
organic mass fraction of the nascent submicron sea spray aerosol.
Predicted relationships between chlorophyll a and organic
fraction are similar to existing empirical parameterizations, but
can vary between biologically productive and nonproductive regions,
and seasonally within a given region. Major uncertainties include
the bubble film thickness at bursting, and the variability of organic
surfactant activity in the ocean, which is poorly constrained. In
addition, polysaccharides may enter the aerosol more efficiently than Langmuir
adsorption would suggest. Potential mechanisms for enrichment of polysaccharides
in sea spray include the formation of marine colloidal particles that may be more
efficiently swept up by rising bubbles, and cooperative adsorption of polysaccharides with proteins or lipids.
These processes may make important contributions to the aerosol, but
are not included here.
This organic fractionation framework is an initial step towards a
closer linking of ocean biogeochemistry and aerosol chemical
composition in Earth system models. Future work should focus on
improving constraints on model parameters through new laboratory
experiments or through empirical fitting to observed relationships
in the real ocean and atmosphere, as well as on atmospheric
implications of the variable composition of organic matter in sea
spray. |
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