Indirect Photochemical Formation of Carbonyl Sulfide and Carbon Disulfide in Natural Waters: Role of Organic Sulfur Precursors, Water Quality Constituents, and Temperature

Abstract

Carbonyl sulfide (COS) and carbon disulfide (CS) are volatile sulfur compounds that are critical precursors to sulfate aerosols, which enable climate cooling. COS and CS stem from the indirect photolysis of organic sulfur precursors in natural waters, but currently the chemistry behind how this occurs remains unclear. This study evaluated how different organic sulfur precursors, water quality constituents, which can form important reactive intermediates (RIs), and temperature affected COS and CS formation. Nine natural waters ranging in salinity were spiked with cysteine, cystine, dimethylsulfide (DMS), or methionine and exposed to simulated sunlight over varying times and water quality conditions. Results indicated that COS and CS formation increased up to 11× and 4×, respectively, after 12 h of sunlight, while diurnal cycling exhibited varied effects. COS and CS formation was also strongly affected by the DOC concentration, organic sulfur precursor type, O concentration, and temperature, while salinity differences and CO addition did not play a significant role. Overall, important factors in forming COS and CS were identified, which may ultimately impact their atmospheric concentrations.

The influence of dissolved organic matter on the marine production of carbonyl sulfide (OCS) and carbon disulfide (CS<sub>2</sub>) in the Peruvian upwelling

“…The reasons for this relationship could result from, e.g., the temperaturedriven decay of precursor molecules, but they remain speculative. The results are in line with findings by Gharehveran and Shah (2018), who found increased CS 2 formation with increasing temperatures in incubation experiments. The surface box model to determine the photoproduction rate constants of CS 2 is set up as a very simple case, including only the processes of photoproduction and air-sea exchange.…”

Photochemical Production of Sulfate and Methanesulfonic Acid from Dissolved Organic Sulfur

“…Based on this latter publication and on mechanistic studies showing COS production from the 341 DOM-photosensitized degradation of cysteine, glutathione and other thiols, [34][35][36][37][38] which are 342 ubiquitous compounds in the environment (Table S4 and In order to understand the relative importance of each degradation pathway, we estimated the product distribution in each DOM sample ( Figure 2C and Table S3). Note that, due to the relatively high experimental errors, volatile product contributions were considered only if…”

Monthly resolved modelled oceanic emissions of carbonyl sulfide and carbon disulfide for the period 2000–2019

“…Diapycnal fluxes into and out of the mixed layer seem to be of minor importance, at least in tropical waters (Lennartz et al, 2019). The photochemical OCS production involves UV-radiation interactions with chromophoric dissolved organic matter (CDOM) (Ferek and Andreae, 1984;Modiri Gharehveran and Shah, 2018;Pos et al, 1998). Apparent quantum yields (AQY) decrease with increasing wavelength, but show orders of magnitude differences between locations (Cutter and Radford-Knoery, 1993;Weiss et al, 1995a;Zepp and Andreae, 1994).…”

“…Apparent quantum yields (AQY) decrease with increasing wavelength, but show orders of magnitude differences between locations (Cutter and Radford-Knoery, 1993;Weiss et al, 1995a;Zepp and Andreae, 1994). Reaction mechanisms involving thiyl radicals have been identified from precursor molecules such as cysteine, cystine and methionine (Modiri Gharehveran and Shah, 2018;Pos et al, 1998). However, the complexity of the natural mixture of dissolved organic sulfur molecules in the ocean (Ksionzek et al, 2016) makes the determination of a photoproduction rate constant on a global scale difficult.…”