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| Titel |
Minor effect of physical size sorting on iron solubility of transported mineral dust |
| VerfasserIn |
Z. B. Shi, M. T. Woodhouse, K. S. Carslaw, M. D. Krom, G. W. Mann, A. R. Baker, I. Savov, G. R. Fones, B. Brooks, N. Drake, T. D. Jickells, L. G. Benning |
| 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 ; 11, no. 16 ; Nr. 11, no. 16 (2011-08-19), S.8459-8469 |
| Datensatznummer |
250010015
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| Publikation (Nr.) |
 copernicus.org/acp-11-8459-2011.pdf |
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| Zusammenfassung |
| Observations show that the fractional solubility of Fe (FS-Fe, percentage of
dissolved to total Fe) in dust aerosol increases considerably from
0.1 % in regions of high dust mass concentration to 80 % in remote regions
where concentrations are low. Here, we combined laboratory geochemical
measurements with global aerosol model simulations to test the hypothesis
that the increase in FS-Fe is due to physical size sorting during transport.
We determined the FS-Fe and fractional solubility of Al (FS-Al) in
size-fractionated dust generated from two representative soil samples
collected from known Saharan dust source regions using a customized dust
re-suspension and collection system. The results show that the FS-Fe is
size-dependent and ranges from 0.1–0.3 % in the coarse size fractions
(>1 μm) to ~0.2–0.8 % in the fine size fractions
(<1 μm). The FS-Al shows a similar size distribution to that of the FS-Fe. The
size-resolved FS-Fe data were then combined with simulated dust mass
concentration and size distribution data from a global aerosol model,
GLOMAP, to calculate the FS-Fe of dust aerosol over the tropical and
subtropical North Atlantic Ocean. We find that the calculated FS-Fe in the
dust aerosol increases systematically from ~0.1 % at high dust mass
concentrations (e.g., >100 μg m−3) to ~0.2 % at low
concentrations (<100 μg m–3) due to physical size sorting (i.e.,
particle gravitational settling). These values are one to two orders of
magnitude smaller than those observed on cruises across the tropical and
sub-tropical North Atlantic Ocean under an important pathway of Saharan dust
plumes for similar dust mass concentrations. Even when the FS-Fe of
sub-micrometer size fractions (0.18–0.32 μm, 0.32–0.56 μm, and
0.56–1.0 μm) in the model is increased by a factor of 10 over the
measured values, the calculated FS-Fe of the dust is still more than an
order of magnitude lower than that measured in the field. Therefore, the
physical sorting of dust particles alone is unlikely to be an important
factor in the observed inverse relationship between the FS-Fe and FS-Al and
the atmospheric mineral dust mass concentrations. The results suggest that
processes such as chemical reactions and/or mixing with combustion particles
are the main mechanisms to cause the increased FS-Fe in long-range
transported dust aerosols. |
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