Abstract
Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Br/Cl/OH/O3) remain unclear, especially in the Southern-Hemisphere. Here, we present latitudinal covariations of Hg and S-isotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OH/O3 in tropics to Br/Cl in polar regions highlighting thus the presence of distinct oxidation processes producing PBM. The correlations between Hg, S and O-isotopic compositions measured in PBM, sulfates and nitrates respectively within the aerosols highlight the implication of common oxidants in their formations at different latitudes. Our results open a new window to better quantify the present-day atmospheric Hg, S and N budgets and to evaluate the influences of aerosols on climate and ecosystems once the isotopic fractionations associated to each process have been determined.
Highlights
Atmospheric models based on either type of Hg0 oxidants (i.e. OH / O3 or Br ) show good agreementsMercury stable isotopes could provide important information on the Hg 0 oxidation pathways because each of them should be associated with specific Hg-isotopic fractionations as demonstrated for halogen oxidants (e.g. Br, Cl )[12] and to be studied for some others including OH and O3
For S-mass-independent fractionation (MIF), suggested that the Hg0 oxidation by halogen the mechanisms suggested to be responsible for producing positive Δ 33S in modern aerosols are stratospheric sulfate inputs into the troposphere 27,28 and/or SO2 oxidation by different oxidants (i.e; H2O2, O3, OH, O2+TMI, BrO, etc.), while negative Δ33S results from a mechanism related to combustion or heterogeneous reaction[17,18,29]
31, we show that the latitudinal isotopic gradients for Hg- and S-MIF in the Southern Hemisphere (SH) indicate a PBM samples are characterized by a δ202Hg varying from -1.7‰ to 1.3‰ while δ34S present a large variation ranging from -2.3‰ to 19.4‰
Summary
Gaseous elemental mercury (GEM, Hg0) is the main atmospheric Hg species, with a lifetime up to 1 year and can be transported worldwide[1]. Hg0 can be oxidized into gaseous oxidized mercury (GOM, HgII), a 10-days lifetime specie which adsorbs readily on particles forming particle-bound Hg (PBM)[1]. Both gaseous and particulate HgII are transferred to terrestrial and marine ecosystems by rainfall and dry deposition. PBM and GOM concentrations controlled by complex atmospheric oxidation and reduction reactions, and the chemical forms (Hg0, HgII) determine its atmospheric lifetime, deposition pathways and ecosystem loadings. Hg redox mechanisms in global Hg transport and chemistry models are ill-constrained, limiting our capacity for science-based Hg emission policy making
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