Kinetics and quantitative spectroscopy for redox chemistry of atmospheric mercury
ORAL
Abstract
Mercury is a common globally pollutant and neurotoxic that has been linked to adverse effects on human health and ecological health. Although gaseous elemental mercury (Hg(0)) dominates mercury emissions to the atmosphere, the rate of oxidation to mercury complex (Hg(II)) plays an important role in determining where and when mercury accumulates in ecosystems. Atomic bromine is known to induce oxidation in the atmosphere via a two-step mechanism.
Hg + Br + M → BrHg + M (R1)
BrHg + Y + M → BrHgY + M (R2)
Where formation of BrHg (R1) and the following reactions of BrHg with abundant free radicals (Y=NO2, NO, HOO, O3, and VOCs) (R2). R1 rate constants were experimentally calculated over a decade ago and the experimental kinetic study on the reaction of R2 was published by Rongrong Wu et al. (for Y = NO2,NO,O2) for the temperature range of 313K to 373K.
We used a laser photolysis-laser induced fluorescence (LP-LIF) spectroscopy setup to assess rate constants vs temperature and pressure in our study. BrHg was produced by 266 nm laser photolysis of HgBr2 vapor. Laser excitation at around 256 nm resulted in laser generated fluorescence of BrHg near 502 nm.
BrHg lives longer at the lower temperatures and pressures prevalent in the middle and upper troposphere. To determine the rate constants of BrHg + Y at atmospheric pressure and temperature conditions we built a new experimental system that allows CRDS and LIF detection to be integrated into a single flow reactor whose temperature spans a large range (223- 373 K).
For the reaction of BrHg + O3;
BrHg + O3 → BrHgO + O2 (R3) alone with two side reactions,
BrHg + O → Hg + BrO (R4)
BrHgO + O → HgBr + O2 (R5)
We present LIF decay measurements obtained by conducting experiments at varying photolysis laser energies to distinguish the individual effects of R3, R4, and R5 on the LIF decays of HgBr, which is possible provided the post-photolysis concentration of O and O3 are accurately known.
Hg + Br + M → BrHg + M (R1)
BrHg + Y + M → BrHgY + M (R2)
Where formation of BrHg (R1) and the following reactions of BrHg with abundant free radicals (Y=NO2, NO, HOO, O3, and VOCs) (R2). R1 rate constants were experimentally calculated over a decade ago and the experimental kinetic study on the reaction of R2 was published by Rongrong Wu et al. (for Y = NO2,NO,O2) for the temperature range of 313K to 373K.
We used a laser photolysis-laser induced fluorescence (LP-LIF) spectroscopy setup to assess rate constants vs temperature and pressure in our study. BrHg was produced by 266 nm laser photolysis of HgBr2 vapor. Laser excitation at around 256 nm resulted in laser generated fluorescence of BrHg near 502 nm.
BrHg lives longer at the lower temperatures and pressures prevalent in the middle and upper troposphere. To determine the rate constants of BrHg + Y at atmospheric pressure and temperature conditions we built a new experimental system that allows CRDS and LIF detection to be integrated into a single flow reactor whose temperature spans a large range (223- 373 K).
For the reaction of BrHg + O3;
BrHg + O3 → BrHgO + O2 (R3) alone with two side reactions,
BrHg + O → Hg + BrO (R4)
BrHgO + O → HgBr + O2 (R5)
We present LIF decay measurements obtained by conducting experiments at varying photolysis laser energies to distinguish the individual effects of R3, R4, and R5 on the LIF decays of HgBr, which is possible provided the post-photolysis concentration of O and O3 are accurately known.
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Publication: -
Presenters
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Achini M Ovitigala
Mississippi State University
Authors
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Achini M Ovitigala
Mississippi State University