Occurrence characteristics and source appointment of per- and polyfluoroalkyl substances (PFAS) in rainwater from megacities to remote cities

Wet deposition serves as a critical process for removing atmospheric pollutants. To explore the occurrence and source disparities of per- and polyfluoroalkyl substances (PFAS) in atmosphere between a megacity and its surrounding areas at varying distances, wet precipitation samples were collected and analyzed from Chengdu (Shuangliu), Wenchuan, and Barkam sites. The results indicated that among the 74 target compounds, approximately 40 PFAS were detected in all samples with perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA) being the predominant monomers, jointly contributing 29.5% to 44.0% of the total PFAS. The highest PFAS wet deposition flux was observed in Chengdu (mean: 1349.86 ng·m -2 ·d -1 ), reflecting the influence of intensive anthropogenic activities. The flux in Wenchuan (1092.47 ng·m -2 ·d -1 ) was 3.73 times higher than that in Barkam (293.25 ng·m -2 ·d -1 ). The Kruskal-Wallis H test and permutational multivariate analysis of variance (PERMANOVA) test revealed that the concentrations, sources or migration processes differed among three locations. The role of long-range transport in governing PFAS occurrence in remote regions-Barkam was convinced by backward trajectory analysis. The finding provided crucial scientific insights for understanding the transport and fate of emerging contaminants at the regional scale.