South-hemispheric marine aerosol Hg and S isotope compositions reveal different oxidation pathways

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 with each process have been determined.