Electrochemical Evidence of non-Volatile Reduced Sulfur Species in Water-Soluble Fraction of Fine Marine Aerosols

Ana Cvitešić Kušan,Irena Ciglenečki,Sanja Frka

doi:10.3390/atmos10110674

Abstract

The traditional voltammetric method at the mercury electrode, and an acidification step developed for the determination of reduced sulfur species (RSS) in natural waters, was for the first time used for the quantification of RSS in the water-soluble fraction of fine marine aerosols collected at the Middle Adriatic location (Rogoznica Lake). The evidence of two types of non-volatile RSS that have different interaction with the Hg electrode was confirmed: mercapto-type which complexes Hg as RS–Hg and sulfide/S0-like compounds which deposits HgS. The analytical protocol that was used for RSS determination in aerosol samples is based on separate voltammetric studies of a methyl 3-mercaptopropionate (3-MPA) as a representative of mercapto-type compounds and sulfide as a representative of inorganic RSS. Our preliminary study indicates the presence of mainly RS–Hg compounds in spring samples, ranging from 2.60–15.40 ng m−3, while both, the mercapto-type (0.48–2.23 ng m−3) and sulfide and/or S0-like compounds (0.02–0.26 ng m−3) were detected in early autumn samples. More expressed and defined RS–Hg peaks recorded in the spring potentially indicate their association with biological activity in the area. Those samples were also characterized by a higher water-soluble organic carbon content and a more abundant surface-active fraction, pointing to enhanced solubility and stabilization of RSS in the aqueous atmospheric phase.

Highlights

In different aquatic ecosystems, electrochemical methods have been widely used for the characterization and determination of different sulfur (S) species, comprising dissolved and/or particulate inorganic and organic S compounds, including thiols ([1,2,3,4,5,6,7,8,9,10,11,12] and references therein)
Accumulation of 3-MPA on Hg at Ed = −0.2 V resulted in the formation of a 3-MPA–Hg complex (Equation (2)), which was reduced by scanning the potential toward more negative values
The position and the height of the 3-MPA–Hg reduction peak is sensitive to the pH of the bulk solution as already noted for other reduced S species (RSS) studied at the Hg surface [2,3,12,15]

Summary

Introduction

Electrochemical methods have been widely used for the characterization and determination of different sulfur (S) species, comprising dissolved and/or particulate inorganic and organic S compounds, including thiols ([1,2,3,4,5,6,7,8,9,10,11,12] and references therein). The methodology is based on the tendency of inorganic and organic reduced S species (RSS) to deposit a HgS layer [1,2,3,4,5,13,14,15] and/or RS–Hg complexes [9,10,15] (term “complex” refers to a different type of interaction between the analyte and the Hg electrode) during an accumulation step at the deposition potential (Ed ) around −0.2 V vs. In solutions containing sulfide anions, an insoluble HgS layer is formed during the deposition step at the Hg surface by the reversible process of a two-electron-transfer oxidation of Hg at potentials more positive than −0.5 V vs the reference electrode (Ag/AgCl). During the potential scan toward negative values, layers of HgS and adsorbable RS–Hg complexes (in the case of DMS, DMDS, cysteine, glutathione) are reduced between

Methods

Results

Conclusion