Distribution and Concentration of Airborne Per- and Polyfluoroalkyl Substances (PFAS) in Indoor and Outdoor Environments: A Systematic Review

Per- and polyfluoroalkyl substances (PFAS) are increasingly recognized as airborne contaminants of concern, yet their distribution across environments remains under-characterized. In particular, concentrations in industry have hardly been studied compared to general environments. This review synthesizes findings from 25 studies reporting airborne PFAS across four categories: outdoor general environments, indoor general environments, outdoor occupational environments, and indoor occupational environments. Reported levels were generally lowest outdoors (0.5–3.0 ng/m 3 ), higher in general indoor settings (3.0–15.0 ng/m 3 ), and highest in occupational environments, sometimes exceeding 100 ng/m 3 . Volatile precursors such as fluorotelomer alcohols dominated most environments, while particle-bound ionic PFAS were more common in occupational settings, suggesting distinct exposure pathways. Across studies, airborne PFAS levels were lowest outdoors, higher indoors, and highest in occupational settings. The complexity of PFAS behavior, influenced by chemical species and particle/gas-phase partitioning, underscores challenges in exposure assessment. Despite the relatively low airborne PFAS concentrations, this review confirms that inhalation remains a critical exposure pathway due to the persistence, bioaccumulation, and toxicity of PFAS. Standardized measurement methods, geographically diverse monitoring, and integration with exposure modeling are urgently needed. Strengthening regulatory frameworks and establishing protective exposure limits will be essential to mitigate long-term health impacts.