Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, United States.
Institut des sciences de la mer, Université du Québec à Rimouski, Rimouski, Québec G5L 3A1, Canada.
Environ Sci Technol. 2024 Sep 10;58(36):16066-16075. doi: 10.1021/acs.est.4c04637. Epub 2024 Aug 23.
Carbonyls have previously been dismissed as significant precursors for carbon monoxide (CO) photoproduction from natural chromophoric dissolved organic matter (CDOM). Here, we used hydrogen cyanide (HCN), which reacts with carbonyls to form photochemically inert cyanohydrins, as a probe to re-examine the role of carbonyls in CO photoproduction. Adding HCN to low-absorbance euphotic zone seawater decreased CO photoproduction. Modeling [HCN] (∼5 to 364 μM) vs the percent decrease in CO photoproduction (%CO↓) yielded carbonyl-cyanohydrin dissociation equilibrium constants, , and maximum %CO↓, %CO↓ values. Four Atlantic and Pacific seawater s (66.7 ± 19.6 μM) overlap aqueous aliphatic but not aromatic aldehyde s. Phenylacetaldehyde (PA) and other β,γ-unsaturated aldehydes are proposed as prototypical CO precursors. Direct photolysis of ∼10 nM PA can supply the measured daily production of HCN-sensitive CO at an open-ocean site near Bermuda. HCN's %CO↓ was 31 ± 2.5% in North Atlantic seawater vs the 13 ± 2.5% inhibition of CO photoproduction by borohydride, a dilemma since only borohydride affects most ketones. Borohydride also decreased CDOM absorption much more than did HCN. This puzzle probably reflects differing steric and solvation requirements in HCN- and borohydride-CDOM reactions. This study demonstrates cyanophilic aldehydes to be a significant source of open-ocean CO and reveals new clues regarding CDOM photochemistry mechanisms.
羰基先前被认为是天然发色溶解有机质 (CDOM) 中一氧化碳 (CO) 光生产的重要前体。在这里，我们使用氢氰酸 (HCN)，它与羰基反应形成光惰性氰醇，作为探针重新研究羰基在 CO 光生产中的作用。向低吸收辐照带海水添加 HCN 会降低 CO 的光生产。模型[HCN]（∼5 至 364 μM）与 CO 光生产降低的百分比（%CO↓）的关系产生了羰基-氰醇离解平衡常数，和最大%CO↓，%CO↓值。四个大西洋和太平洋海水样本（66.7 ± 19.6 μM）重叠水相脂肪醛但不重叠芳香醛。苯乙醛 (PA) 和其他β，γ-不饱和醛被认为是 CO 前体的原型。在百慕大附近的开阔海域，约 10 nM 的 PA 直接光解可以提供测量到的每天 HCN 敏感 CO 的产量。在北大西洋海水中，HCN 的%CO↓为 31 ± 2.5%，而硼氢化钠对 CO 光生产的抑制作用为 13 ± 2.5%，这是一个难题，因为只有硼氢化钠会影响大多数酮。硼氢化钠对 CDOM 吸收的影响也远大于 HCN。这个难题可能反映了 HCN 和硼氢化钠与 CDOM 反应在空间和溶剂化方面的不同要求。本研究表明亲氰醛是开阔海域 CO 的重要来源，并揭示了 CDOM 光化学机制的新线索。
