Uher Günther, Pillans J Julian, Hatton Angela D, Upstill-Goddard Robert C
School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom.
School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom.
Chemosphere. 2017 Nov;186:805-816. doi: 10.1016/j.chemosphere.2017.08.050. Epub 2017 Aug 11.
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 to 0.345 h) and DMSO photo-production (0.017 h to 0.283 h) 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, a. Variations in a explained 61% (R = 0.61, n = 26) and 73% (R = 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, 0.019 d, and 0.017 d 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.
在对来自英格兰东北部（泰恩河口）和苏格兰西部（林尼湖以及泰努伊特的南特河）沿海样本进行的26次实验室辐照实验中，对二甲基硫（DMS）的光氧化作用和二甲基亚砜（DMSO）的光生成情况进行了评估。DMS光氧化作用（0.038 h⁻¹至0.345 h⁻¹）和DMSO光生成作用（0.017 h⁻¹至0.283 h⁻¹）的准一级反应速率常数变化幅度达一个数量级，且在北海沿岸地区最低。河口样本（盐度S < 30）的DMSO平均产率为96 ± 16%（n = 14），这与通过单线态氧的光敏氧化作用实现1:1摩尔转化相符。光化学速率常数与350 nm处的有色溶解有机物（CDOM）吸收系数a密切相关。a的变化分别解释了DMS光氧化作用和DMSO生成作用中61%（R = 0.61，n = 26）和73%（R = 0.73，n = 17）的变异性。然而，CDOM归一化光化学速率常数朝着CDOM吸光度最低的沿海水域大幅增加，这表明具有海洋特征的水样（S > 30）对DMS光氧化作用的反应性最强。通过按平均日辐照度（7月，英格兰东北部）和中紫外水下辐照度进行缩放得到的水柱平均DMS光氧化速率常数估计值，对于上河口（S < 20）、下河口（20 < S < 30）和沿海水域（S > 30）分别为0.012 d⁻¹、0.019 d⁻¹和0.017 d⁻¹，处于先前观测值的下限。将我们的水柱平均DMS光氧化速率常数与通过海 - 气气体交换估计的DMS损失以及先前报道的生物消耗量进行比较，意味着DMS的光化学去除在我们的研究区域中仅具有次要重要性。
