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| Titel |
Enhanced production of oxidised mercury over the tropical Pacific Ocean: a key missing oxidation pathway |
| VerfasserIn |
F. Wang, A. Saiz-Lopez, A. S. Mahajan, J. C. Gómez Martín, D. Armstrong, M. Lemes, T. Hay, C. Prados-Roman |
| 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. 3 ; Nr. 14, no. 3 (2014-02-05), S.1323-1335 |
| Datensatznummer |
250118354
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| Publikation (Nr.) |
 copernicus.org/acp-14-1323-2014.pdf |
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| Zusammenfassung |
| Mercury is a contaminant of global concern. It is transported in the
atmosphere primarily as gaseous elemental mercury, but its reactivity and
deposition to the surface environment, through which it enters the aquatic
food chain, is greatly enhanced following oxidation. Measurements and
modelling studies of oxidised mercury in the polar to sub-tropical marine
boundary layer (MBL) have suggested that photolytically produced bromine atoms are
the primary oxidant of mercury. We report year-round measurements of
elemental and oxidised mercury, along with ozone, halogen oxides (IO and BrO)
and nitrogen oxides (NO2), in the MBL over the
Galápagos Islands in the equatorial Pacific. Elemental mercury
concentration remained low throughout the year, while higher than expected
levels of oxidised mercury occurred around midday. Our results show that the
production of oxidised mercury in the tropical MBL cannot
be accounted for by bromine oxidation only, or by the inclusion of ozone and hydroxyl. As a two-step oxidation
mechanism, where the HgBr intermediate is further oxidised to Hg(II), depends
critically on the stability of HgBr, an additional oxidant is needed to react
with HgBr to explain more than 50% of the observed oxidised mercury.
Based on best available thermodynamic data, we show that atomic iodine,
NO2, or HO2 could all play the potential role of the missing
oxidant, though their relative importance cannot be determined explicitly at
this time due to the uncertainties associated with mercury oxidation
kinetics. We conclude that the key pathway that significantly enhances
atmospheric mercury oxidation and deposition to the tropical oceans is
missing from the current understanding of atmospheric mercury oxidation. |
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