Sources and Transformation Mechanisms of AtmosphericParticulate Bound Mercury Revealed by Mercury Stable Isotopes

This study examined the isotopic composition ofparticulate bound mercury (PBM) in 10 Chinese megacities andexplored the associated sources and transformation mechanisms. PBMin these cities was characterized by negative delta 202Hg (mean:-2.00 to-0.78 parts per thousand), slightly negative to highly positive Delta 199Hg (mean:-0.04 to0.47 parts per thousand), and slightly positive Delta 200Hg (mean: 0.02 to 0.06 parts per thousand) values.ThepositivePBM Delta 199Hg signatures were likely caused byphysiochemical reactions in aerosols. The Delta 199Hg/Delta 201Hg ratio variedfrom 0.94 to 1.39 in the cities and increased with the increase in thecorresponding mean Delta 199HgPBMvalue. We speculate that, in addition tothe photoreduction of oxidized Hg, other transformation mechanismsin aerosols (e.g., isotope exchange, complexation, and oxidation, whichexpress nuclear volume effects) also shape the Delta 199HgPBMsignatures inthe present study. These processes are likely enhanced in the presenceof strong gas-particle partitioning of gaseous oxidized Hg (GOM) and elevated levels of redox active metals (e.g., Fe), halides, andelemental carbon. Based on Delta 200HgPBMdata presented in this and previous studies, we estimate that large proportions (similar to 47 +/- 22%)of PBM were sourced from the oxidation of gaseous elemental Hg followed by the partitioning of GOM onto aerosols globally,indicating the transformation of Hg(0) to PBM as an important sink of atmospheric Hg(0)