Mass transfer coefficients for volatilization of polychlorinated biphenyls from the Hudson River,New York measured using micrometeorological approaches |
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Authors: | Andy L Sandy Jia Guo Robert J Miskewitz Wade R McGillis Lisa A Rodenburg |
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Institution: | 1. Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, USA;2. Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, NY, USA;3. Earth and Environmental Engineering, Columbia University, New York, NY, USA |
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Abstract: | Air–water exchange is an important process controlling the fate of many organic chemicals in the environment. Modeling this process is hampered by the lack of direct observations. Thus, the purpose of this work was to derive direct measurements of the mass transfer coefficients for air–water exchange (vaw) of polychlorinated biphenyls (PCBs) that may be used to check the validity of values derived from tracer gas experiments. vaw values for PCBs were determined using previously published turbulent fluxes divided by the corresponding dissolved phase concentrations. The median vaw values for each homolog decreased with increasing molecular weight and ranged from 0.29 for hexachlorobiphenyls to 2.2 m d?1 for monochlorobiphenyls with a propagated uncertainty of about 70%, lower than in previous studies. Due to relatively low wind speeds and possible sorption of PCBs to colloids, these numbers may be biased low. These field measurements of vaw differ by as much as a factor of 23 from predictions based on the widely-used Whitman two-film model. Therefore a new formulation for the calculation of vaw based on field measurements is needed. This study demonstrates that micrometeorological approaches are a viable option for the measurement of vaw for hydrophobic organics such as PCBs and should be used to generate enough field data on the air–water exchange of hydrophobic organics to allow the development of new predictive models. |
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