Ionic PFAS in PM_2.5 and dust: Insights on indoor-outdoor profiles and distribution

Although extensive studies have been performed to characterize Per- and polyfluoroalkyl substances (PFAS) in the environment, PFAS in PM_2.5 remains underexplored. This study presents a comprehensive investigation of PFAS in indoor and outdoor PM_2.5 and dust samples to evaluate their quantities and distribution. Twenty-nine ionic PFAS species were quantified in samples collected from ten different environments such as daycare center, vehicle, airport, and fire training facility. PFAS were found to be ubiquitous, and present in both PM_2.5 (3.34-22.2 pg/m³) and dust (1.27-9840 ng/g). Perfluoroalkyl carboxylic acids (PFCAs) dominated the PFAS profile in both indoor and outdoor PM_2.5, accounting for 94.1 ± 11.1% of total PFAS, which was significantly higher than that in dust (61.5 ± 32.7%) (p < 0.01). In contrast, the proportion of perfluoroalkane sulfonic acids (PFSAs) in dust (21.7 ± 18.1%) was significantly higher than that in PM_2.5 (4.54 ± 10.5%) (p < 0.01). This suggests that PFCAs are more likely than PFSAs to attach to PM_2.5, and are capable of long-range atmospheric transport (LRT). Among the 11 PFCAs species, perfluorobutanoic acid (PFBA) and perfluorohexanoic acid (PFHxA), two short chain PFAS, were of the highest concentrations, particularly in samples collected during the wildfire events. This highlights the significance of short chain PFAS in LRT. For indoor PFAS, a strong relationship (r = 0.611-0.853, p < 0.01) was observed between long-chain PFCAs concentrations in PM_2.5 and in dust. These findings provide new insights into the potential processes of indoor PFCAs emissions and distribution and suggest possible exposure pathways of airborne PFAS in urban environments.