Controlled chamber formation of per- and polyfluoroalkyl substances (PFAS) aerosols with <i>Pseudomonas fluorescens</i> : size distributions, effects, and inhalation deposition potential

Abstract. Per- and polyfluoroalkyl substances (PFAS) are recognised as atmospheric contaminants, yet processes governing their aerosol formation, size distribution, and interactions with atmospheric particle surfaces remain unknown. We investigated aerosolisation and size-resolved behaviour of 25 PFAS covering short-, medium-, and long-chain perfluoroalkyl carboxylic acids (PFCA), perfluoroalkane sulfonates, fluorotelomer sulfonates and emerging alternatives. Experiments were conducted under controlled chamber conditions using a water–organic solvent system, in the absence/presence of the model bacterium Pseudomonas fluorescens seed to investigate the potential influence of microbial presence on PFAS behaviour. Most PFAS exhibited unimodal mass–size distributions peaking at 0.3 µm, indicating dominant association with the fine mode. Sulfonated PFAS showed broadly similar aerosol-phase concentrations regardless of carbon-chain length, whereas PFCA displayed increasing aerosolisation with chain length. Perfluorooctane sulfonic acid (PFOS) showed additional ultrafine enrichment, 6:2 fluorotelomer sulfonate (6:2 FTS) and sodium 4,8-dioxa-3H-perfluorononanoate (NaDONA) exhibited broader size profiles, suggesting compound-specific effects linked to volatility and interfacial behaviour. Pseudomonas fluorescens seed did not enhance PFAS aerosol concentrations through condensation or heterogeneous uptake onto bacterial particles or shift in modal diameters, and no enrichment was observed at bacterial size mode, indicating limited PFAS–bioaerosol association under the tested conditions. Multiple-Path Particle Dosimetry (MPPD) modelling based on the measured size distributions predicted substantial deposition of the aerosol-bound PFAS in the pulmonary region, particularly for compounds enriched in ultrafine particles. Our findings indicate that PFAS aerosol behaviour in mixed-solvent systems is controlled primarily by physical droplet generation and evaporation, with implications for airborne transport and inhalation exposure from contaminated aqueous sources.