Beyond the tropopause hypothesis: Drivers of even mercury isotope fractionation unraveled by 3D modeling.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40971418.
- Also identified by DOI 10.1126/sciadv.adx8401 and PMC identifier 12448055.
- Licence recorded as CC BY-NC.
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Abstract
Mercury (Hg) is a globally persistent contaminant with substantial health impact. The mass-independent fractionation of even mercury isotopes (even-MIF, denoted as Δ<sup>200</sup>Hg) is widely used to trace atmospheric Hg sources and fluxes. However, the chemical processes inducing even-MIF remain largely unknown. Here, we develop a three-dimensional atmospheric Hg isotope model linking Hg redox processes with even-MIF. The results show that the previous hypothesis of even-MIF occurring exclusively at the tropopause may not fully explain the global Δ<sup>200</sup>Hg patterns. We speculate OH-initiated reactions and photoreduction of Hg<sup>II</sup>(p) as likely dominant drivers. Simulations show that even-MIF primarily originates in the free troposphere and propagates downward to surface air. Our results reveal distinct spatial Δ<sup>200</sup>Hg variations that were previously unaccounted for in tracing Hg sources. This study provides critical insights into even-MIF drivers and serves as a reference for using Δ<sup>200</sup>Hg to trace atmospheric Hg sources.