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Titel |
Uncertainties in the determination of the organic fraction of global sea-spray emissions |
VerfasserIn |
Monique Albert, Claire Scannell, Gerrit de Leeuw, Martijn Schaap, Colin O'Dowd |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250037299
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Zusammenfassung |
Sea-spray aerosol considerably affects the climate, both directly and indirectly. The emission
rate of sea-spray droplets per unit area of the sea surface is implemented in climate models
through a sea-spray source function. The uncertainty between existing formulations of the
sea-spray source function that is parameterized in terms of wind speed and sea surface
temperature is more than a factor of 2.
Organic material substantially contributes to the composition of sea-spray aerosols,
especially in biological active regions. Small sea-spray particles may be mainly composed of
organic carbon with a decreasing contribution as particle size increases. The sizes in which
organic carbon occurs are in the active CCN range and a change in composition may thus
have a substantial effect on cloud droplet formation. A first attempt to include the OC fraction
of sea-spray in a sea-spray source function was presented by O’Dowd et al. (2008).
These authors proposed to use remotely sensed chlorophyll concentration data as a
proxy for oceanic biological activity. An organics-chlorophyll relationship was
determined by correlating chlorophyll satellite data and in-situ measurements of water
insoluble organic compounds. This information was used together with the sea-spray
source function to determine the surface flux of the combined inorganic/organic
sea-spray particles (O’Dowd et al., 2008; Vignati et al., 2009; Albert et al., 2010). By
introducing this methodology one inevitably introduces uncertainties due to the
choice of a certain satellite instrument to obtain the chlorophyll data and the choice
of the resolution and compositing period of the data. Other uncertainties that are
introduced are due to the handling of the satellite data and the fit that is used in the
organics-chlorophyll correlation. The organic fraction estimate can additionally be affected
by the time period that is studied and the source function that is used to calculate the total
sea-spray emission. We will first present a basis methodology to estimate the global
emission of the submicron organic matter fraction of sea-spray. Starting from a first
estimate of the annual global emission we have performed a sensitivity analysis
regarding the above mentioned uncertainties. We found differences of up to at least 50%
depending on the chosen parameterizations. Especially the choice of different source
functions and the fit that was used in the organics-chlorophyll correlation were found to
cause large deviations from our first estimate. From this we can conclude that the
estimation of the fraction of organic matter in submicron sea-spray aerosol is still very
uncertain.
REFERENCES
Albert, M.F.M.A., M. Schaap, G. de Leeuwand P.J.H. Builtjes (2010). Progress in the
determination of the sea spray source function from satellite data. Journal of Integrative
Environmental Sciences, accepted.
O’Dowd, C.D. et al., 2008. A combined organic-inorganic sea-spray source function.
Geophysical Research Letters, 35(L01801).
Vignati E, Facchini MC, Rinaldi M, Scannell C, Ceburnis D, Sciare J, Kanakidou M,
Myriokefalitakis S, Dentener F and O’Dowd CD. 2009. Global scale emission and
distribution of sea spray aerosol: sea-salt and organic enrichment. Atmospheric Environment,
accepted. |
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