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Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters

Lookup NU author(s): Dr Guenther Uher, Professor Robert Upstill-Goddard

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Dimethylsulphide (DMS) photo-oxidation and dimethylsulphoxide (DMSO) photoproduction were estimated in 26 laboratory irradiations of coastal samples from NE England (Tyne estuary) and W Scotland (Loch Linnhe and River Nant at Taynuilt). Pseudo-first order rate constants of DMS photo-oxidation (0.038 h-1 to 0.345 h-1) and DMSO photo-production (0.017 h-1 to 0.283 h-1) varied by one order of magnitude and were lowest in the coastal North Sea. Estuarine samples (salinity S<30) had a mean DMSO yield of 96±16% (n=14), consistent with 1:1 molar conversion via photosensitised oxidation by singlet oxygen. Photochemical rate constants were strongly correlated with coloured dissolved organic matter (CDOM) absorption coefficients at 350 nm, a350. Variations in a350 explained 61% (R2=0.61, n=26) and 73% (R2=0.73, n=17) of the variability in DMS photo-oxidation and DMSO production, respectively. However, CDOM normalised photochemical rate constants increased strongly towards coastal waters exhibiting lowest CDOM absorbance, indicating water samples of marine character (S>30) to be most reactive with respect to DMS photo-oxidation. Estimates of water column averaged DMS photo-oxidation rate constants, obtained by scaling to mean daily irradiance (July, NE England) and mid-UV underwater irradiance, were 0.012 d-1, 0.019 d-1, and 0.017 d-1 for upper estuary (S<20), lower estuary (20<S<30) and coastal waters (S>30), at the lower end of previous observations. Comparing our water column averaged DMS photo-oxidation rate constants with estimated DMS losses via air-sea gas exchange and previously reported biological consumption implies that DMS photochemical removal is of only minor importance in our study area.


Publication metadata

Author(s): Uher G, Pillans JJ, Hatton AD, Upstill-Goddard RC

Publication type: Article

Publication status: Published

Journal: Chemosphere

Year: 2017

Volume: 186

Pages: 805-816

Print publication date: 01/11/2017

Online publication date: 11/08/2017

Acceptance date: 10/08/2017

ISSN (print): 0045-6535

Publisher: Elsevier

URL: https://doi.org/10.1016/j.chemosphere.2017.08.050

DOI: 10.1016/j.chemosphere.2017.08.050


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