Influence of Dissolved Organic Matter on Carbonyl Sulfide and Carbon Disulfide Formation from Dimethyl Sulfide During Sunlight Photolysis.

Abstract

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 photo-production from dimethyl sulfide (DMS) in the presence of dissolved organic matter (DOM). DOM was added since it photochemically produces various reactive intermediates (3 CDOM*, • OH, 1 O2 , and H2 O2 ) 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 3 CDOM* 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 non-detect levels. DOM type influenced COS only at higher concentrations (20 mg/L), while increasing DOM concentrations proportionally increased COS concentrations for all DOM types. Phenol addition lowered COS formation for reasons that remained unclear since phenol likely quenched 3 CDOM* and DMS-derived sulfur-based radicals. Further comparisons to 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.