Use of experimentally determined Henry's Law and salting-out constants for ethanol in seawater for determination of the saturation state of ethanol in coastal waters

- Henry's Law Constants for ethanol are given for salinity to 36 and 1-35 °C.
- The salting-out coefficient for ethanol is 0.13 M−1 in solutions up to 4 M NaCl.
- High dissolved organic carbon does not affect Henry's Law Constants.
- The percent saturation in surface waters is driven by changes in air concentrations.

The Henry's law constant for ethanol in seawater was experimentally determined to be 221 ± 4 M/atm at 22 °C compared with 247 ± 6 M/atm in pure water. The salting out coefficient for ethanol was 0.13 M−1. In seawater ln(KH) = -(12.8 ± 0.7) + (5310 ± 197)/T where KH is in M atm−1 and temperature is in K. This plus the salting out coefficient allow calculation of KH for any estuarine or sea water between 1 and 35 °C. High concentrations of dissolved organic carbon do not affect KH values in fresh or seawater. Nearshore surface waters were usually undersaturated with respect to gas phase ethanol except when air concentrations decreased, whereas surface seawater 40 km from shore was supersaturated. The percent saturation in surface waters is driven primarily by changes in air concentrations because these change quickly (hours) and more extensively than surface water. This study allows calculation of ethanol saturation states from air and surface water concentrations which is a necessary step to define the role of surface oceans in the global biogeochemical cycling of ethanol both now and in the future as use of ethanol biofuel continues to grow.

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