Influence of dissolved organic matter on carbonyl sulfide and carbon disulfide formation from dimethyl sulfide during sunlight photolysis

• Published in: Water environment research 2021-12, Vol.93 (12), p.2982-2997
• Main Authors: Modiri Gharehveran, Mahsa, Shah, Amisha D.
• Format: Article
• Language: English
• Subjects: Atmospheric gases; Carbon; Carbon Disulfide; Carbonyl compounds; Carbonyl sulfide; Carbonyls; Dimethyl sulfide; Dissolved organic carbon; Dissolved Organic Matter; Freshwater; Gases; Hydrogen peroxide; Inland water environment; Intermediates; Natural waters; Phenols; Photolysis; Photoproduction; Precursors; Sulfides; Sulfur; Sulfur Oxides; Sulphides; Sulphur; Sunlight
• ISSN: 1061-4303; 1554-7531
• DOI: 10.1002/wer.1650

Carbonyl sulfide (COS) and carbon disulfide (CS2) are important atmospheric gases photochemically generated from organic sulfur precursors in sunlit natural waters. This study examined these processes by evaluating COS and CS2 photoproduction from dimethyl sulfide (DMS) in the presence of dissolved organic matter (DOM). DOM was added because it photochemically produces various reactive intermediates (3CDOM*, •OH, 1O2, and H2O2) potentially involved in these reaction pathways. DMS‐amended synthetic waters at pH 8 were varied in terms of their DOM type and concentration, spiked with the 3CDOM* quenching agent, phenol, in certain cases, and subsequently irradiated over varying exposure times. Results indicated that various DOM types ranging from freshwater to open‐ocean DOM increased COS but did not alter CS2, which remained at nondetect levels. DOM type influenced COS only at higher concentrations (20 mg/L), whereas increasing DOM concentrations proportionally increased COS concentrations for all DOM types. Phenol addition lowered COS formation for reasons that remained unclear because phenol likely quenched 3CDOM* and DMS‐derived sulfur‐based radicals. Further comparisons with DMS‐spiked natural waters and cysteine (CYS)‐spiked synthetic and natural waters assessed previously indicated that COS formation from both precursors in natural waters was always greater than in waters containing DOM alone. Practitioner Points DMS‐ and DOM‐spiked synthetic waters formed COS but did not form CS2 during sunlight photolysis. In DMS‐spiked synthetic solutions, DOM type has a limited influence on COS formation whereas DOM concentration has a stronger influence on COS formation. COS formation in the DMS‐spiked synthetic waters was fairly proportional to the DOC concentration but was generally lower than COS formation in DMS‐spiked natural waters. Sunlight exposure of dimethyl sulfide (DMS) in water containing dissolved organic matter (DOM) generates carbonyl sulfide (COS) through indirect photochemical pathways. The process does not generate carbon disulfide (CS2) above nondetect levels. The extent of COS formation is highly dependent on DOM concentration and less so on DOM type.