Photoinitiated\nDegradation Kinetics of the Organic\nUV Filter Oxybenzone in Solutions and Aerosols: Impacts of Salt, Photosensitizers,\nand the Medium

Organic UV filters like oxybenzone (BP3) in sunscreens\nare seawater\npollutants suspected to transfer to the atmosphere via sea spray aerosol\n(SSA). This study examines the photoinitiated degradation of BP3 in\nartificial and real seawater compared to SSA mimics containing NaCl\nand 4-benzoylbenzoic acid (4-BBA). We investigated pure, binary, and\nternary mixtures of BP3, NaCl, and 4-BBA using solar-simulated light\nto isolate the effects of salt and photosensitization on BP3 degradation.\nResults showed significantly faster degradation in the aerosol phase\n(<i>J</i><sub>eff,env</sub> ≈ 10<sup>–3</sup>–10<sup>–2</sup> s<sup>–1</sup> or <i>t</i><sub>1/2</sub> < 10 min) compared to bulk solutions (<i>J</i><sub>eff,env</sub> ≈ 10<sup>–6</sup> s<sup>–1</sup> or <i>t</i><sub>1/2</sub> > 1 day). The photosensitizer\nenhanced BP3 photodegradation in both phases more than when mixed\nwith salt or all three components in solutions. BP3 photodegradation\nwas most enhanced by salt in the aerosol phase. High-resolution molecular\nanalysis via Orbitrap LC-MS/MS revealed more acutely toxic compounds\n(benzophenone, benzoic acid, and benzaldehyde) in irradiated aerosols\nthan in solution, supported by electronic structure and toxicity modeling.\nThese findings highlight that seawater may serve as a reservoir for\nBP3 and other organic UV filters and that upon transfer into SSA,\nBP3 rapidly transforms, increasing aerosol toxicity.