Abstract

The acid dissociation constants (pKas) of perfluoroalkyl carboxylic acids (PFCAs) have been the subject of discussion in the literature; for example, values from -0.2 to 3.8 have been suggested for perfluorooctanoic acid (PFOA). The dissociated anionic conjugate bases of PFCAs have negligible air-water partition coefficients (KAWs) and do not volatilize from water. The neutral acids, however, have relatively high KAWs and volatilization from water has been demonstrated. The extent of volatilization of PFCAs in the environment will depend on the water pH and their pKa. Knowledge of the pKas of PFCAs is therefore vital for understanding their environmental transport and fate. We investigated the water-to-air transfer of PFCAs in a novel experimental setup. We used ∼1 μg L(-1) of PFCAs in water (above environmental background concentrations but below the concentration at which self-association occurs) at different water pH (pH 0.3 to pH 6.9) and sampled the PFCAs volatilized from water during a 2-day experiment. Our results suggest that the pKas of C4-11 PFCAs are "1.6. For PFOA, we derived a pKa of 0.5 from fitting the experimental measurements with a volatilization model. Perfluoroalkane sulfonic acids were not volatilized, suggesting that their pKas are below the investigated pH range (pKa "0.3).

Abstract

In 2007, under contract to the UK Department for Transport, we engaged with the public about the infrastructure to supply hydrogen for transport. We combined a quota-sample survey of 1003 across three disparate ‘travel-to-work areas’ in England with focus groups representative of them. We informed the groups ‘at arm's length’ through a purpose-made video, composed with advice from a hydrogen scientist and made by professional broadcasters. Participants saw benefits in hydrogen energy. None rejected it on safety grounds, though many discussed the risks. The costs were considered a problem. ‘The public’ was not of one mind. Regular car drivers were unwilling to reduce their car use. Bus users, cyclists and walkers often sought improvements in air quality. Motorists knew more than others about hydrogen energy. In discussion we seek psychological and socio-cultural explanations for these results. We conclude by drawing out implications for the future of hydrogen in transport.