Atmospheric Oxidation of PFAS by Hydroxyl Radical: A Density Functional Theory Study

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent, widely spread, and harmful pollutants. They can travel through the air, be transformed by radicals, and deposit into water or onto surfaces. They enter the atmosphere via direct emission, degradation of precursors, or aerosol formation. A recent investigation found novel compounds in rainwater, meaning PFAS may undergo transformations in the atmosphere. These transformations might exhibit distinct behavior compared to more well-researched reactions, creating difficulties in the identification of any new compounds being produced. Using density functional theory (DFT), we simulated reactions of PFAS with a major atmospheric radical, the hydroxyl radical, revealing activation energies and other thermodynamic insights. The activation energies aid in predicting likely reactions and understanding speciation. Identifying new species can guide future analyses and remediation efforts. We focused on the nine most widely studied families of PFAS, finding that radical abstraction along the alkyl chain is favored over functional groups regardless of chain length. These results establish a new foundation for understanding PFAS transformations in the atmosphere, especially when decarboxylation is not followed.