Ionic PFAS in PM2.5 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/m 3 ) 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. • Daycare PM 2.5 showed the richest PFAS diversity, with 6:2 FTS dominating daycare dust. • Short-chain PFCAs (C 4 –C 7 ) in PM 2.5 rose notably during wildfire-affected days. • PM 2.5 –dust exchange in vehicles may increase exposure to PM 2.5 -bound PFAS. • Indoor PM 2.5 and dust showed strong correlations for several long-chain PFCAs. • Long-chain PFCAs are low-volatility PFAS, yet vapor pressure still affects indoor settling.