Air-Sea Gas Exchange under Nature-Like Surfactant Influence in the Lab

For the first time, air-sea gas exchange measurements under the influence of four surface active substances also found in the sea surface microlayer were performed in the Aeolotron wind-wave tank. Chosen surfactants were Dextran which is water soluble, as well as the insoluble substances Mono-Galactosyl-Diacylglycerol, Palmitic Acid and Phosphatidylglycerol. Gas transfer velocities of N2O and C2HF5 were measured using a mass balance approach combined with FT-IR spectroscopic methods. In addition, wave parameters like the mean square slope of the water surface were monitored. It was found that Dextran alone does not significantly decrease the gas transfer velocity compared to the clean water surface, while reduction for the full mix of surfactants was as high as 70%. For the full mix of surfactants, at a wind speed of around 7m/s the surfactant film ruptured and was mixed down into the water bulk where it was inefficient in suppressing gas transfer.