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 (Br•/Cl•/OH•/O 3 ) remain unclear, especially in the Southern Hemisphere. Here, we present latitudinal covariations of Hg and Sisotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OH•/O 3 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.

Toward the Origins of Quadruple Sulfur Isotope Anomalies in Modern Sulfate: A Multitracer Approach and Implications for Paleo- and Planetary Atmospheres

“…For simplicity, we assume the isotopic compositions of starting SO 2 to be δ 34 S = Δ 33 S = Δ 36 S = 0‰, and the quadruple sulfur isotope pattern of sulfate produced from various SO 2 oxidation pathways is shown in Figure . It is clear that Δ 33 S and Δ 36 S anomalies of modern sulfate aerosols in this study and in the literature ,,,,,− , do not fall in the nonzero Δ 33 S and Δ 36 S spaces due to SO 2 oxidation (Figure ). Therefore, S-MIF processes must be invoked to explain Δ 33 S and Δ 36 S anomalies observed in modern sulfate aerosols.…”

“…Quadruple sulfur isotope compositions of sulfate aerosols in this study (stars) and comparisons with global aerosol data in the literature ,,,,− (dots). The Δ 36 S value of the empty star is an outlier (see the main text and Table ).…”

“…54,55 It remains unclear where the radical pair reaction is involved in the formation of black crust sulfate. Most recently, new studies of aerosol collected at India and open oceans argue that heterogeneous sulfate formation on mineral surface results in positive Δ 33 S values, 18,19 in contrast to previous arguments (negative Δ 33 S values). 15−17 In addition, the correlation between Δ 33 S and mineral dusts highly depends on the selection of mineral dust tracers.…”

“…23 In addition, if carbon contamination did occur during analytical processes, carbonrich coal samples would not show near-zero Δ 36 S values. 11 Similarly, levoglucosan concentrations of aerosol samples collected at Seoul in 2019 (<50 ng m −3 ) 46 are comparable 10,11,15,18,19,[36][37][38][39]43 (symbols are the same as Figure 1). (A) δ 34 S/Δ 33 S; (B) δ 34 S/Δ 36 S; and (C) Δ 33 S/ Δ 36 S. Quadruple sulfur isotope compositions of coals collected from China are also shown as solid squares.…”

“…Based on the possible production of S-MIF in sulfur recombination reactions that may occur in gaseous thermochemical reactions such as combustion and volcanism, it is further argued that similar processes may occur in Archean, providing additional non-photochemical S-MIF processes that may need to be considered in interpreting Archean data. , This idea was preliminarily tested by physical chemistry experiments and atmospheric chemistry models . Subsequent multiple sulfur isotope measurements of modern sulfate aerosols however found that Δ 33 S anomalies are also correlated with mineral dusts. − It was preliminarily proposed that heterogeneous sulfur reactions account for such Δ 33 S anomalies, but Δ 33 S signs among different follow-up studies are different. − A deep mechanistic understanding on the possible chemical reaction that may lead to Δ 33 S anomalies is useful for using Δ 33 S to identify and quantify any missing sulfate formation pathway in the modern atmosphere with profound implications for air pollution and climate change. − …”