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| Titel |
Composition and properties of atmospheric particles in the eastern Atlantic and impacts on gas phase uptake rates |
| VerfasserIn |
J. D. Allan, D. O. Topping, N. Good, M. Irwin, M. Flynn, P. I. Williams, H. Coe, A. R. Baker, M. Martino, N. Niedermeier, A. Wiedensohler, S. Lehmann, K. Müller, H. Herrmann, G. McFiggans |
| 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 ; 9, no. 23 ; Nr. 9, no. 23 (2009-12-11), S.9299-9314 |
| Datensatznummer |
250007793
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| Publikation (Nr.) |
 copernicus.org/acp-9-9299-2009.pdf |
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| Zusammenfassung |
Marine aerosol composition continues to represent a large source of
uncertainty in the study of climate and atmospheric chemistry. In addition
to their physical size and chemical composition, hygroscopicity plays a
significant role, increasing the particles' surface areas and scattering
potential. Simultaneous aerosol measurements were performed on board the RRS
Discovery and at the Cape Verde atmospheric observatory during the Aerosol
Composition and Modelling in the Marine Environment (ACMME) and Reactive
Halogens in the Marine Boundary Layer (RHAMBLE) experiments. These included
online measurements of number and dry size and bulk collection for offline
analysis of aqueous ions. In addition, the measurements on board the
Discovery included online measurements of composition using an Aerodyne
Aerosol Mass Spectrometer, optical absorption using a Multi Angle Absorption
Photometer, ambient humidity size distribution measurements using a
humidified differential mobility particle sizer (DMPS) and optical particle
counter (OPC) and hygroscopicity measurements with a hygroscopicity tandem
differential mobility analyser (HTDMA).
Good agreement between platforms in terms of the sea salt (ss) and non sea
salt (nss) modes was found during the period when the Discovery was in close
proximity to Cape Verde and showed a composition consistent with remote
marine air. As the Discovery approached the African coast, the aerosol
showed signs of continental influence such as an increase in particle
number, optical absorption, enhancement of the nss mode and dust particles.
The Cape Verde site was free of this influence during this period. Chloride
and bromide showed concentrations with significant deviations from seawater
relative to sodium, indicating that atmospheric halogen processing (and/or
acid displacement for chloride) had taken place. The time dependent ambient
size distribution was synthesised using humidified DMPS and OPC data,
corrected to ambient humidity using HTDMA data. Heterogeneous uptake rates
of hypoiodous acid (HOI) were also predicted and the nss accumulation mode
was found to be the most significant part of the size distribution, which
could act as an inert sink for this species. The predicted uptake rates were
enhanced by around a factor of 2 during the African influence period due to
the addition of both coarse and fine particles.
The hygroscopicity of the nss fraction was modelled using the Aerosol
Diameter Dependent Equilibrium Model (ADDEM) using the measured composition
and results compared with the HTDMA data. This was the first time such a
reconciliation study with this model has been performed with marine data and
good agreement was reached within the resolution of the instruments. The
effect of hygroscopic growth on HOI uptake was also modelled and ambient
uptake rates were found to be approximately doubled compared to equivalent
dry particles. |
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