Accelerated Fatty Acid Oxidation Occurs at the Water–Air Interface of Sea Spray Microdroplets

The oxidation of organic molecules, such as fatty acids, in seawater microdroplets generated by breaking waves is an important source of secondary organic aerosols and impacts the global climate. While the oxidation of fatty acids in sea spray aerosols (SSAs) has traditionally been attributed to photochemical reactions, this study reports a spontaneous nonphotochemical oxidation mechanism that occurs in seawater microdroplets. Notably, we observed marked increases in the oxidation rate (3186- to 11093-fold) for the naturally abundant fatty acids docosahexaenoic acid, oleic acid, and palmitic acid, with the primary oxidation products being hydroxylated. Integrated computational simulations and mass spectrometry analyses of reaction paths and intermediates suggest that this rapid oxidation is triggered by the simultaneous accumulation of fatty acids and the spontaneous generation of hydroxy radicals (•OH) at the microdroplet water-air interface. Our study revealed an overlooked path of fatty acid oxidation, shedding light on organic carbon cycles at the ocean-atmosphere interface.