Abstract
Abstract. Organosulfur compounds (OSCs) are naturally emitted via various processes involving phytoplankton and algae in marine regions, from animal metabolism, and from biomass decomposition inland. These compounds are malodorant and reactive. Their oxidation to methanesulfonic and sulfuric acids leads to the formation and growth of atmospheric particles, which are known to influence clouds and climate, atmospheric chemical processes. In addition, particles in air have been linked to negative impacts on visibility and human health. Accurate measurements of the OSC precursors are thus essential to reduce uncertainties in their sources and contributions to particle formation in air. Two different approaches, proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) and canister sampling coupled to gas chromatography with flame ionization detector (GC-FID), are compared for both laboratory standards (dimethyl sulfide, DMS; dimethyl disulfide, DMDS; dimethyl trisulfide, DMTS; and methanethiol, MTO) and for a complex sample. Results show that both techniques produce accurate quantification of DMS. While PTR-ToF-MS provides real-time measurements of all four OSCs individually, significant fragmentation of DMDS and DMTS occurs, which can complicate their identification in complex mixtures. Canister sampling coupled with GC-FID provides excellent sensitivity for DMS, DMDS, and DMTS. However, MTO was observed to react on metal surfaces to produce DMDS and, in the presence of hydrogen sulfide, even DMTS. Avoiding metal in sampling systems seems to be necessary for measuring all but dimethyl sulfide in air.
Highlights
We report a comparison between two techniques for the measurements of Organosulfur compounds (OSCs) in air, including direct real-time measurements by proton-transfer reaction time-offlight mass spectrometry (PTR-ToF-MS) and offline stainless steel canister sampling coupled to gas chromatography with flame ionization detector (GC-FID)
It was not possible to determine accurately the absolute permeation rate for Dimethyl trisulfide (DMTS) due to large variations in the weight of the tube and the presence of some Dimethyl disulfide (DMDS) in the outflow; even if the gas-phase generation system could not be used for absolute calibration of DMTS, as described in Sect. 3.3, it was useful for the stability study in which only relative mixing ratios were needed
Signal response and fragmentation patterns in the PTRToF-MS were investigated from the analysis of the pure OSC standards (Fig. 1)
Summary
Organosulfur compounds (OSCs) such as methanethiol (CH3SH, MTO), dimethyl sulfide (CH3SCH3, DMS), dimethyl disulfide (CH3SSCH3, DMDS), and dimethyl trisulfide (CH3SSSCH3, DMTS) have been measured in air (Nguyen et al, 1983; Andreae et al, 1985; Andreae, 1990; Andreae et al, 1993; Aneja, 1990; Bates et al, 1992; Watts, 2000; de Bruyn et al, 2002; Xie et al, 2002; Jardine et al, 2015). Atmospheric particles have been previously linked to negatively affect health and visibility (Dockery et al, 1993; Hinds, 1999; Pope III et al, 2002; Pope III and Dockery, 2006) Because of their key role in the formation of new particles in air, it is critical to account for all sources of OSCs. Several sample collection strategies have been applied over the years to the measurement of OSCs in air including the use of Tedlar® chambers (Hansen et al, 2011), metal canister or glass vessel-based methods (Kesselmeier et al, 1993; Williams et al, 1999; Simpson et al, 2001; Meinardi et al, 2003; Blunden et al, 2005; Trabue et al, 2008; Beyersdorf et al, 2010; Guo et al, 2010; Khan et al, 2012; Meinardi et al, 2013; Zhang et al, 2013), solid sorbents (Filipy et al, 2006) or sorptive metal (Andreae et al, 1985), solid-phase microextraction (Xie et al, 2002; Lestremau et al, 2004), and cryotraps (Hofmann et al, 1992; de Bruyn et al, 2002). Advantages and challenges associated with these two techniques are discussed with respect to sampling complex mixtures
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