Mass transfer rates between oil slicks and water

The results of a laboratory wind‐wave tank study are reported in which the rate of mass transfer of a tracer (phenol) from a synthetic oil slick to the underlying water was measured at wind speeds from 0 to 9 m/s. Estimates were made of the mass transfer coefficients in the oil and water phases at the oil‐water interface. The results indicate that the rate of hydrocarbon dissolution from a slick is controlled by the water phase mass transfer coefficient which is usually less than 1 cm/h. Whereas mass transfer coefficients at air‐water interfaces show a marked increase at wind speeds of approximately 3 m/s due to wave formation, when oil is present its damping effect delays this transition to approximately 7 m/s. It can be inferred that (i) dissolution is considerably slower than evaporation for reasonably volatile compounds, (ii) dissolution will have a negligible effect on slick composition, (iii) the concentrations of soluble hydrocarbons established in the water column under the slick by direct dissolution are small and unlikely to result in significant toxicity, and (iv) that the dominant mechanism of transfer of soluble hydrocarbons into the water column is probably from dissolution of dispersed oil particles.