Influence of convective and stratiform precipitation types on per- and polyfluoroalkyl substance concentrations in rain

Atmospheric transport and wet deposition have contributed to the worldwide distribution of per- and polyfluoroalkyl substances (PFAS) in terrestrial and aquatic ecosystems, even in remote areas far from known industrial sources. However, little is known regarding the impact of cloud and precipitation formation dynamics on PFAS transport and wet deposition, nor the range of variability in PFAS concentrations within a closely distributed monitoring network. Precipitation samples were collected from a network of 25 stations in a focused geographic region (the Commonwealth of Massachusetts, USA) from stratiform and convective storm systems to evaluate if the different cloud and precipitation formation mechanisms in these two fundamental types of storm systems influenced PFAS concentrations in precipitation, and to assess the range of variability in PFAS concentrations in precipitation at a regional scale. PFAS were detected in 11 of 50 discrete precipitation events. Of the 11 events from which PFAS were detected, 10 of the events were convective in nature. PFAS were detected during only one stratiform event at one station. This suggests that local and regional atmospheric PFAS sources entrained by convection events controls regional atmospheric PFAS flux, and that PFAS flux estimates should consider the type and magnitude of precipitation events. The PFAS detected were primarily perfluorocarboxylic acids, with relatively higher detection frequency for shorter-chained compounds. Compilation of PFAS data from precipitation across primarily the eastern United States, from urban, suburban, and rural areas, including those in industrial areas, indicates population density is a poor predictor of precipitation PFAS concentrations. While the total PFAS concentration in precipitation in some areas exceeds 100 ng/L, the median concentrations across all areas are generally less than about 10 ng/L.