TY - JOUR
T1 - Measurement-based modelling of bromine-induced oxidation of mercury above the Dead Sea
AU - Tas, E.
AU - Obrist, D.
AU - Peleg, M.
AU - Matveev, V.
AU - Faïn, X.
AU - Asaf, D.
AU - Luria, M.
PY - 2012
Y1 - 2012
N2 - Atmospheric mercury depletion events (AMDEs) outside the polar region-driven by high levels of gaseous Br and BrO (i.e., BrO x)-were observed recently in the warm Dead Sea boundary layer. The efficient oxidation of gaseous elemental mercury (GEM) under temperate conditions by BrO x 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 k Hg+Br and k Hg+BrO of 2.7 × 10 -13 cm 3 molecule -1 s -1 and 1.5 × 10 -13 cm 3 molecule -1 s -1, respectively. Our model also predicted that a rate constant k Hg+BrO of 5.0 × 10 -14 cm 3 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 BrO x 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.
AB - Atmospheric mercury depletion events (AMDEs) outside the polar region-driven by high levels of gaseous Br and BrO (i.e., BrO x)-were observed recently in the warm Dead Sea boundary layer. The efficient oxidation of gaseous elemental mercury (GEM) under temperate conditions by BrO x 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 k Hg+Br and k Hg+BrO of 2.7 × 10 -13 cm 3 molecule -1 s -1 and 1.5 × 10 -13 cm 3 molecule -1 s -1, respectively. Our model also predicted that a rate constant k Hg+BrO of 5.0 × 10 -14 cm 3 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 BrO x 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.
UR - http://www.scopus.com/inward/record.url?scp=84857961933&partnerID=8YFLogxK
U2 - 10.5194/acp-12-2429-2012
DO - 10.5194/acp-12-2429-2012
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AN - SCOPUS:84857961933
SN - 1680-7316
VL - 12
SP - 2429
EP - 2440
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
IS - 5
ER -