Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters

Günther Uher*, J. Julian Pillans, Angela D. Hatton, Robert C. Upstill-Goddard

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Citations (SciVal)

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 M 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.

Original languageEnglish
Pages (from-to)805-816
Number of pages12
JournalChemosphere
Volume186
Early online date17 Aug 2017
DOIs
Publication statusPublished - 01 Nov 2017
Externally publishedYes

Keywords

  • Coloured dissolved organic matter
  • North Sea
  • Photochemistry
  • Reduced sulfur compounds
  • Seawater
  • Tyne estuary
  • Sulfides/analysis
  • Water Pollutants, Chemical/analysis
  • Models, Chemical
  • Oxidation-Reduction
  • England
  • Estuaries
  • Scotland
  • Rivers
  • Dimethyl Sulfoxide/analysis
  • Photochemical Processes
  • Seawater/chemistry

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