The reaction between HgBr and O₃: kinetic study and atmospheric implications

Abstract

The rate constants of many reactions currently considered to be important in the atmospheric chemistry of mercury remain to be measured in the laboratory. Here we report the first experimental...

Together, not separately, OH and O3 oxidize Hg(0) to Hg(II) in the atmosphere

“…Our CCSD(T) and CAM-B3LYP-D3BJ values of k7 at 298 K fall 13% above and 12% below, respectively, the recently obtained experimental value, 58 providing strong support for the validity of our computational approach. We predict a minimal temperature-dependence of this rate constant, which supports the reasonableness of the assumption of temperature independence made in two a recent modeling studies.…”

“…Our CAM-B3LYP-D3BJ and CCSD(T) rate constants at 298 K (6.5 and 8.7 × 10 -11 cm 3 molec -1 s -1 ) bracket the experimental value of 7.5 ± 0.6 × 10 -11 cm 3 molec -1 s -1 (at 295 K). 58 The rate constants computed at CAM-B3LYP-D3BJ and CCSD(T) are nearly temperature independent (Figure 6). They vary by only ~20% over the range 200 K ≤ T ≤ 360 K. The NEVPT2 rate constant at 298 K is a factor of 14 lower than the experimental value, and increases monotonically with increasing temperature by a factor of 2.4 over the same temperature range.…”

“…If the rate constant, k9, for reduction for BrHg (I) were to be non-negligible, it would interfere with the analysis of experimental data used by Gomez Martin et al to determine k7. 58 The inclusion of R8 in a model of global mercury redox chemistry enormously increased the importance of OH-initiation oxidation of Hg (0) to Hg (II) , to the extent that ~40% of HOHg (I) was converted to HOHg (II) O. 55 Because BrHg (I) is more stable than HOHg (I) , close to 100% of it is converted to BrHg (II) O.…”

“…19 Very recently, Gomez Martin et al carried out the first determination of the rate constant of R7 using laser-flash photolysis with laser-induced fluorescence: 7.5 ± 0.6 × 10 -11 cm 3 molec -1 s -1 (at 295 K). 58 They assumed the reaction proceeded via R7.…”

“…In this study, we use computational chemistry to determine the kinetics of oxidation of HOHg (I) by O3 (R8) and compare the kinetics of R8 with the analogous reaction of BrHg (I) (R7). The comparison to R7 holds particular value in light of two facts: the recent experimental determination of k7(295 K) 58 and the complete absence of experimental data on gas-phase HOHg (I) . In addition, we also study the reduction of YHg (I) to Hg (0) by ozone:…”