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Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters

Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters
Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters
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.
0045-6535
805-816
Uher, Günther
fa6a86d9-ff48-411c-8cb7-80b6d50708c9
Pillans, J. Julian
ea1d9783-d20a-4c9c-9dbd-32c49fdfeb44
Hatton, Angela D.
90503a09-db5a-4f27-91eb-13e58ecb4432
Upstill-goddard, Robert C.
2df7187e-9875-407d-a529-e9bd90042d23
Uher, Günther
fa6a86d9-ff48-411c-8cb7-80b6d50708c9
Pillans, J. Julian
ea1d9783-d20a-4c9c-9dbd-32c49fdfeb44
Hatton, Angela D.
90503a09-db5a-4f27-91eb-13e58ecb4432
Upstill-goddard, Robert C.
2df7187e-9875-407d-a529-e9bd90042d23

Uher, Günther, Pillans, J. Julian, Hatton, Angela D. and Upstill-goddard, Robert C. (2017) Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters. Chemosphere, 186, 805-816. (doi:10.1016/j.chemosphere.2017.08.050).

Record type: Article

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.

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Accepted/In Press date: 10 August 2017
Published date: 1 November 2017

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Local EPrints ID: 415227
URI: http://eprints.soton.ac.uk/id/eprint/415227
ISSN: 0045-6535
PURE UUID: 9896ba50-f827-40cd-aa4e-76ce49e273c4

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Date deposited: 03 Nov 2017 17:30
Last modified: 15 Mar 2024 16:41

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Contributors

Author: Günther Uher
Author: J. Julian Pillans
Author: Angela D. Hatton
Author: Robert C. Upstill-goddard

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