Interfacial chemistry of trifluoroacetic acid and SO₃: Unanticipated pathways contributing to aerosols in polluted marine atmospheres

Marine atmospheric aerosols are pivotal components of the global aerosol system, which can significantly influence global climate and human health. Perfluoroalkyl carboxylic acids (PFCAs), persistent emerging contaminants, exhibit pronounced enrichment in sea spray aerosols (SSAs). However, current gas-particle partitioning models underestimate their particulate-phase ratios in polluted atmospheres. Here, we elucidate the interfacial chemistry driving the enrichment of PFCAs in SSAs under anthropogenic impacts. Through Born-Oppenheimer molecular dynamics simulations, we demonstrated that TFA, a representative of PFCAs, exhibited activity at gas-liquid interfaces. The carbonyl oxygen of TFA protrudes beyond hydration layers, which facilitates collisions with gaseous SO₃. Interfacial water molecules can promote simultaneous TFA deprotonation and SO₃ collision and then the formation of trifluoroacetic acid sulfuric anhydride ions (TFASA⁻) and hydronium ions (H₃O⁺). TFASA⁻ displays superior hygroscopicity over precursors, enhancing the growth potential of SSAs to form cloud condensation nuclei (CCN). Given the continuous accumulation of PFCAs in marine environment, the interfacial chemical reactions between PFCAs and reactive pollutants (e.g., SO₃) in marine atmospheres need urgent focus to understand the influence of PFCAs on marine particulate matter pollution and global climate.