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| Titel |
Measurement-based modelling of bromine-induced oxidation of mercury above the Dead Sea |
| VerfasserIn |
E. Tas, D. Obrist, M. Peleg, V. Matveev, X. Faïn, D. Asaf, M. Luria |
| 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 ; 12, no. 5 ; Nr. 12, no. 5 (2012-03-05), S.2429-2440 |
| Datensatznummer |
250010853
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| Publikation (Nr.) |
 copernicus.org/acp-12-2429-2012.pdf |
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| Zusammenfassung |
Atmospheric mercury depletion events (AMDEs) outside the polar region –
driven by high levels of gaseous Br and BrO (i.e., BrOx) – were
observed recently in the warm Dead Sea boundary layer. The efficient
oxidation of gaseous elemental mercury (GEM) under temperate conditions by
BrOx was unexpected considering that the thermal back dissociation
reaction of HgBr is about 2.5 orders of magnitude higher under Dead Sea
temperatures compared to polar temperatures, and hence was expected to
significantly slow down GEM oxidation under warm temperatures. The goal of
this modelling study was to improve understanding of the interaction of
reactive bromine and mercury during Dead Sea AMDEs using numerical
simulations based on a comprehensive measurement campaign in summer 2009.
Our analysis is focused on daytime AMDE when chemical processes dominate
concentration changes. Best agreements between simulations and observations
were achieved using rate constants for kHg+Br and kHg+BrO of
2.7 × 10−13 cm3 molecule−1 s−1 and
1.5 × 10−13 cm3 molecule−1 s−1, respectively. Our
model also predicted that a rate constant kHg+BrO of
5.0 × 10−14 cm3 molecule−1 s−1 may be considered
as a minimum, which is higher than most reported values. These rate
constants suggest that BrO could be a more efficient oxidant than Br in the
troposphere as long as [Br]/[BrO] ratios are smaller than ~0.2 to 0.5. Under
Dead Sea conditions, these kinetics demonstrate a high efficiency and
central role of BrOx for AMDEs, with relative contributions to GEM
depletion of more than ~90%. Unexpectedly, BrO was found to be the
dominant oxidant with relative contributions above 80%. The strong
contribution of BrO could explain why the efficiency of GEM oxidation at the
Dead Sea does not critically depend on Br and, therefore, is comparable to
that in cold polar regions. In order to confirm the suggested kinetics,
additional studies, particularly for temperature-dependence of rate
constants, are required. |
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