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| Titel |
Iodine speciation in rain, snow and aerosols |
| VerfasserIn |
B. S. Gilfedder, S. C. Lai, M. Petri, H. Biester, T. Hoffmann |
| 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 ; 8, no. 20 ; Nr. 8, no. 20 (2008-10-21), S.6069-6084 |
| Datensatznummer |
250006414
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| Publikation (Nr.) |
 copernicus.org/acp-8-6069-2008.pdf |
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| Zusammenfassung |
| Iodine oxides, such as iodate, should be the only thermodynamically stable
sink species for iodine in the troposphere. However, field observations have
increasingly found very little iodate and significant amounts of iodide and
soluble organically bound iodine (SOI) in precipitation and aerosols. The
aim of this study was to investigate iodine speciation, including the
organic fraction, in rain, snow, and aerosols in an attempt to further
clarify aqueous phase iodine chemistry. Diurnal aerosol samples were taken
with a 5 stage cascade impactor and a virtual impactor (PM2.5) from the
Mace Head research station, Ireland, during summer 2006. Rain was collected
from Australia, New Zealand, Patagonia, Germany, Ireland, and Switzerland
and snow was obtained from Greenland, Germany, Switzerland, and New Zealand.
Aerosols were extracted from the filters with water and all samples were
analysed for total soluble iodine (TSI) by inductively coupled plasma mass
spectrometry (ICP-MS) and iodine speciation was determined by coupling an
ion chromatography unit to the ICP-MS. The median concentration of TSI in
aerosols from Mace Head was 222 pmol m−3 (summed over all impactor
stages) of which the majority was associated with the SOI fraction (median
day: 90±4%, night: 94±2% of total iodine). Iodide
exhibited higher concentrations than iodate (median 6% vs. 1.2% of
total iodine), and displayed significant enrichment during the day compared
to the night. Interestingly, up to 5 additional, presumably anionic
iodo-organic peaks were observed in all IC-ICP-MS chromatograms, composing
up to 15% of the TSI. Soluble organically bound iodine was also the
dominant fraction in all rain and snow samples, with lesser amounts of
iodide and iodate (iodate was particularly low in snow). Two of the same
unidentified peaks found in aerosols were also observed in precipitation
from both Southern and Northern Hemispheres. This suggests that these
species are transferred from the aerosols into precipitation and that they
have either a relatively long lifetime or are rapidly recycled. It is
thought that SOI is formed by reactions between HOI or I2 and organic
matter derived from the ocean surface layer. SOI may then photolytically
decompose to yield iodide and the unidentified species. The data in this
study show that iodine oxides are the least abundant species in rain, snow,
and aerosols and therefore considerably more effort is required on aqueous
phase iodine chemistry for a holistic understanding of the iodine cycle. |
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