Computational Study on the Photolysis of BrHgONO and the Reactions of BrHgO^• with CH₄, C₂H₆, NO, and NO₂: Implications for Formation of Hg(II) Compounds in the Atmosphere

Abstract

Global models suggest BrHgONO to be the major Hg(II) species initially formed in atmospheric oxidation of Hg(0) in most of the atmosphere, but its atmospheric fate has not been previously investigated. In the present work, we use quantum chemistry to predict that BrHgONO photolysis produces the thermally stable radical BrHgO•. Subsequently, BrHgO• may react with NO2 to form thermally stable BrHgONO2, or with NO to re-form BrHgONO. Additionally, BrHgO• abstracts hydrogen atoms from CH4 and C2H6 with higher rate constants than does •OH, producing a stable BrHgOH molecule. Because BrHgO• can abstract hydrogen atoms from sp3-hybridized carbons on many organic compounds, we expect production of BrHgOH to dominate globally, although formation of BrHgONO and BrHgONO2 may compete in urban regions. In the absence of experimental data on the kinetics and fate of BrHgONO and BrHgO•, we aim to guide modelers and other scientists in their search for Hg(II) compounds in the atmosphere.