Sea spray aerosol as a newly identified source of atmospheric gas-phase perfluoroalkyl carboxylic acids

Abstract. Perfluoroalkyl carboxylic acids (PFCAs) are persistent environmental contaminants found throughout different ecosystems, including the global oceans. Many of these compounds are bio-accumulative and toxic. Previous studies have shown that sea spray aerosol (SSA), formed by wave breaking and subsequent bubble bursting, is enriched in PFCAs and provides a means for their condensed-phase transport from the oceans to the atmosphere. This has been considered as a main pathway for PFCA distribution to even remote regions of the Arctic and Antarctic, impacting human and ecosystem health far away from sources. Here we present novel evidence that PFCAs transported into the atmosphere via SSA may subsequently partition to the gas phase. This previously unconsidered process may cause particle-only measurements and models to underestimate the total atmospheric PFCA burden associated with SSA emissions. Our field observations from the Eastern North Atlantic Ocean and laboratory studies using a high-resolution time-of-flight chemical ionisation mass spectrometer (HR-ToF-CIMS) reveal that the amount of gaseous PFCAs released from SSA may exceed particle-phase concentrations and depends primarily on the low pH of SSA particles, a result of the concentration of ocean water components in the particles upon formation and drying. To date, this mechanism has not been considered in estimates of oceanic PFCA emissions, indicating an underestimation of this source also for PFCA deposition. We encourage future studies to perform a systematic analysis of gas-phase PFCA emissions from SSA during different seasons and locations, both in field and controlled laboratory settings to constrain this newly identified source of gas-phase PFCAs.