A neurotoxic pollutant capable of long-range transport, mercury (Hg) endangers both human health and ecosystems globally. Emitted directly in elemental form, Hg(0) does not readily enter the ecosystems until being oxidized to Hg(II) compounds. The oxidation of Hg(0) to Hg(II) largely limits the rate at which mercury enters the ecosystems, yet much of its mechanism remains unknown. Atomic bromine (Br●) has been known to initiate the oxidation, and BrHgONO has been identified as the major subsequent Hg(II) species. The photolysis of BrHgONO rapidly produces BrHgO●, an intermediate which has been characterized by previous theoretical studies to be thermally stable, despite the absence of experimental data on the radical. Consequently, BrHgO● has a sufficiently long lifetime to react with trace organic gases. We present the potential energy profiles for the reactions of BrHgO● with NO, NO2, and a few trace organic compounds (CH4, C2H6, HCHO, and C2H4) at the CCSD(T)//M06-2X level of theory. Temperature-dependent rate constants for a subset of reactions were calculated using variational transition state theory (VTST) and asymmetric Eckart tunneling. BrHgO● may efficiently abstract hydrogen atoms from alkanes and aldehydes, or undergo addition reactions with NO, NO2, alkenes, and aldehydes. Our results further predict the abstraction product BrHgOH to be a significant fate of BrHgO●. In the absence of experimental data on BrHgONO and BrHgO● kinetics, our work seeks to provide guidance for modelers and field scientists in identifying atmospheric Hg(II) compounds.

Chemistry of BrHgO●: Predicting atmospheric fate of a previously-unknown intermediate of mercury oxidation

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.