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

Abstract

Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Brž/Clž/OHž/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 OHž/O3 in tropics to Brž/Clž 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.

Isotope Data Constrains Redox Chemistry of Atmospheric Mercury

“…The three scenarios (Run1–3) simulate drastically different odd-MIF of Hg II (P) [Δ 199 Hg II (P) and Δ 201 Hg II (P)] in the global atmosphere (Figure S1), even though all reproduce the global spatial variability of observed TGM and wet deposition (see Supporting Information Appendix, Text S1). We synthesized globe observations of Δ 199 Hg II (P) and Δ 201 Hg II (P) that contain sites in land and MBL (Figure A). ,,− , , − ,− We find that Run1 simulates Δ 199 Hg II (P) and Δ 201 Hg II (P) values (0.04 ± 0.29‰ and 0.05 ± 0.29‰, respectively) comparable to observations (0.08 ± 0.29‰ and 0.06 ± 0.27‰, respectively). Moreover, only Run1 produces comparable Δ 199 Hg II (P) and Δ 201 Hg II (P) values across the three categorized observations (Table S2).…”

“…However, recent isotope data have raised uncertainties regarding the Hg 0 oxidation pathway in the MBL. For instance, based on cross-hemispheric sulfur and Hg isotope data on marine aerosols, AuYang et al proposed that Hg oxidation is primarily driven by OH/O 3 in the tropics, transitioning to Br/Cl in polar regions. On the other hand, Yu et al and Qiu et al found that Hg 0 oxidation in North Hemisphere tropical and temperate MBL is mainly initiated by Br through Hg isotope analysis.…”

“…Qiu et al collected and analyzed Hg isotope information from 16 total suspended particle samples in the marginal seas of South and Southeast Asia in 2016. AuYang et al reported Hg isotope information from 42 marine aerosol samples collected along the cruise track from Shanghai, China, to East Antarctica from 2015 to 2016. We have synthesized the specific information, including the sampling time and locations, and utilized this data for evaluation purposes.…”

“…MIF includes odd- (odd-MIF, reported as Δ 199 Hg and Δ 201 Hg) and even-mass-number isotope MIF (even-MIF, reported as Δ 200 Hg and Δ 204 Hg). , MDF is observed in almost all physical, chemical, and biological processes, while even-MIF is known to occur exclusively in photochemical reactions at free troposphere and/or tropopause. , Particularly, significant odd-MIF predominantly occurs in certain Hg photochemical transformations, such as the reduction of Hg II and the oxidation of atmospheric Hg 0 . − Mercury stable isotopes thus have the potential to trace the chemical processes of atmospheric Hg. The isotope signatures of Hg II (P), formed by redox chemistry, can reflect the information on redox processes, as demonstrated by the field studies conducted in urban, rural, and MBL regions. ,− While these studies have provided insights into atmospheric Hg chemistry, they are limited in space and time and cannot fully capture the heterogeneity of the global atmosphere.…”

“…Synthesis of observations and simulations in odd-MIF of Hg II (P) in the globe. ,,− , , − ,− (A) Global map marked with available observations for Δ 199 Hg and Δ 201 Hg of Hg II (P) samples (B–G) Comparison of simulations (annual mean) with measurements for Δ 199 Hg II (P) and Δ 201 Hg II (P) in the global atmosphere. In the figure, the arrows indicate that the photoreduction process can shift the Δ 199 Hg II (P) and Δ 201 Hg II (P) toward positive values, while the oxidation process has the opposite effect.…”