Isotope Data Constrains Redox Chemistry of Atmospheric Mercury

The redox chemistry of mercury (Hg) in the atmosphere
exerts a
significant influence on its global cycle. However, our understanding
of this important process remains shrouded in uncertainty. In this
study, we utilize three-dimensional atmospheric Hg isotope modeling
to evaluate the isotopic composition of particle-bound mercury [HgII(P)] in the global atmosphere. We investigate various chemistry
mechanisms and find that they induce remarkably disparate odd-number
mass-independent fractionation (odd-MIF) in HgII(P) on
a global scale. The observed odd-MIF data identify the essential role
of sea salt aerosol debromination in the redox chemistry of atmospheric
Hg and underscore the predominant influence of Br oxidation in the
marine boundary layer. The odd-MIF signatures significantly narrow
the uncertainty range of redox chemistry rates and constrain the photoreduction
of HgII(P) at a magnitude of 10–3 JNO2 (local photolysis frequency of NO2) in the global atmosphere. This study advances our understanding
of atmospheric Hg chemistry processes and provides insights into the
potential impacts of climate change on Hg cycling.