Photochemical Degradation of Sunscreen Chemicals in Sea Spray Aerosols

In coastal tourist areas, the frequent use of sunscreen has led to the substantial release of its chemical components into the marine environment. Recent studies have demonstrated that sunscreen chemicals can undergo sea-to-air transport via sea spray aerosols (SSA). However, their transformation behavior and environmental fate in the aerosol phase remain poorly understood. This study reports the heterogeneous oxidation kinetics and mechanisms of three typical sunscreen chemicals (4-methylbenzylidene camphor (4-MBC), benzophenone-4 (BP-4), and propylparaben (PrPB)) initiated by hydroxyl radicals (OH) in the aerosol phase composed of sea salt and organic matter. The measured heterogeneous rate constants for reactions with OH ranged from 2.07 × 10⁻¹² to 4.52 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, corresponding to an average atmospheric lifetime of approximately 41-89 h, indicating their potential for long-distance transport before degradation. Through the characterization of the components of aged aerosols, it was found that the functionalization reactions play a key role in the oxidation process, and the unexpected decrease in the O/C ratio of BP-4 products was attributed to sulfonic group loss. In addition, the dithiothreitol (DTT) assay indicated that the aged aerosols exhibit an overall low oxidative potential. These findings enhance our understanding of the environmental behavior and potential atmospheric impact of sunscreen chemicals in SSA.