Potential role of sea spray generation in the atmospheric transport of perfluorocarboxylic acids
ABSTRACT The observed environmental concentrations of perfluorooctanoic acid (PFOA) and its conjugate base (PFO) in remote regions such as the Arctic have been primarily ascribed to the atmospheric transport and degradation of fluorotelomer alcohols (FTOHs) and to direct PFO transport in ocean currents. These mechanisms are each capable of only partially explaining observations. Transport within marine aerosols has been proposed and may explain transport over short distances but will contribute little over longer distances. However, PFO(A) has been shown to have a very short half-life in aqueous aerosols and thus sea spray was proposed as a mechanism for the generation of PFOA in the gas phase from PFO in a water body. Using the observed PFO concentrations in oceans of the Northern Hemisphere and estimated spray generation rates, this mechanism is shown to have the potential for contributing large amounts of PFOA to the atmosphere and may therefore contribute significantly to the concentrations observed in remote locations. Specifically, the rate of PFOA release into the gas phase from oceans in the Northern Hemisphere is calculated to be potentially comparable to global stack emissions to the atmosphere. The subsequent potential for atmospheric degradation of PFOA and its global warming potential are considered. Observed isomeric ratios and predicted atmospheric concentrations due to FTOH degradation are used to elucidate the likely relative importance of transport pathways. It is concluded that gas phase PFOA released from oceans may help to explain observed concentrations in remote regions. The model calculations performed in the present study strongly suggest that oceanic aerosol and gas phase field monitoring is of vital importance to obtain a complete understanding of the global dissemination of PFCAs.
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ABSTRACT: Here we estimate the importance of vertical eddy diffusion in removing perfluorooctanoic acid (PFOA) from the surface Ocean and assess its importance as a global sink. Measured water column profiles of PFOA were reproduced by assuming that vertical eddy diffusion in a 3-layer ocean model is the sole cause for the transport of PFOA to depth. The global oceanic sink due to eddy diffusion for PFOA is high, with accumulated removal fluxes over the last 40 years of 660 t, with the Atlantic Ocean accounting for 70% of the global oceanic sink. The global oceans have removed 13% of all PFOA produced to a depth greater than 100 m via vertical eddy diffusion; an additional 4% has been removed via deep water formation. The top 100 m of the surface oceans store another 21% of all PFOA produced (∼1100 t).Environmental Pollution 05/2013; 179C:88-94. DOI:10.1016/j.envpol.2013.04.006 · 3.90 Impact Factor
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ABSTRACT: Nonylphenol ethoxylates (NPEOs) are environmentally ubiquitous non-ionizing surfactants that show a preference for the air–water interface. They are therefore potentially subject to enhanced transport by aqueous aerosols. The extent to which aqueous aerosols affect the overall environmental fate and behavior of NPEOs is investigated with a combination of laboratory and field experiments and mathematical modeling. Aqueous aerosol droplets were generated in a laboratory-based experimental system. Aqueous aerosols were measured to have concentrations of NPEOs at least four times greater than in the bulk source water.The concentration of nonylphenol and nonylphenol monoethoxylate in aqueous aerosols off the coast of Bermuda were 4.3–19.2 times higher than in coastal water and open water collected from the Bermuda Atlantic Time Series sampling site. Coastal water showed higher concentrations than open water samples ranging from 36 to 51 ng L−1 and 14 to 21 ng L−1 respectively. Depth profiling showed a loss of detection below 300 m. Aqueous aerosol enrichment was demonstrated and relative atmospheric concentrations ranged from 0.28 to 1.8 ng m−3. A generic marine model was developed using independent North Sea data to estimate the relative potential for NPEO transfer within spray droplets to the atmosphere and subsequently into the gas phase by volatilization. The results were compared to the estimated direct volatilization from the surface of a natural water body. The upward mass flux of NPEOs by direct volatilization was comparable in magnitude to the fluxes due to spray generation, depending on the wind speed and droplet sizes. The experimental results and the model calculations were illustratively applied to reported NPEO concentrations in the North Sea. Aerosol generation provides a feasible mechanism for atmospheric transport of NPEOs and their degradation products, nonylphenols (NPs).Atmospheric Environment 04/2013; 69:304–312. DOI:10.1016/j.atmosenv.2012.11.066 · 3.06 Impact Factor
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ABSTRACT: This study critically evaluates the recently published measurement and modelling studies of the sources and fate of perfluorinated carboxylates (PFCAs). It is concluded that modelling studies provide support to the 'direct hypothesis' for PFOA and PFNA (i.e. the global dominance of direct sources (mainly from fluoropolymer manufacturing)). Empirical evidence for the importance of direct sources of PFOA and PFNA is provided by PFNA : PFOA ratios and isomer profiles of PFOA in ocean water. However, homologue patterns of long-chain PFCAs in biota from remote regions suggest that indirect sources (mainly from precursor degradation) are proportionally more important for PFCAs with more than 10 carbons. Temporal data in biotic and abiotic media are reviewed and an increasing trend to 2000 is observed for all PFCAs, with discrepancies in time trends reported after that period. Some studies on temporal patterns report a levelling off or decline in the latter part of the 2000s for PFOA and PFNA, whereas others show a continual increase throughout the study period. Differences in temporal patterns result from the fact that some environments respond faster to emission changes than others and may thus be useful to elucidate the importance of direct and indirect sources to different regions.Environmental Chemistry 08/2011; 8(4):339-354. DOI:10.1071/EN10144 · 3.04 Impact Factor