It is very difficult to disentangle the mechanisms of air-sea gas exchange with field experiments because all available measurement techniques provide insufficient spatial and temporal resolution and do not provide direct insight into the processes occurring in the thin mass boundary layers at the water interface.This talk presents results from the annular wind-wave facility (Heidelberg Aeolotron), the Large Air-Sea Interaction Facility (LASIF) at the University of Marseille, the Kyoto High Wind Speed Facility, and the SUSTAIN facility at the Rosenstiel School of Marine and Atmospheric Science (RSMAS) at the University of Miami, obtained over the last decade. We used thermographic techniques and imaging concentration fields in the mass boundary layer together with classical mass balance techniques.Wind shear is the driving factor except for very small wind speeds, but the mechanisms change with wind speed. Although surfactants significantly alter the mechanisms, monolayers do not directly resist gas transfer. The role of bubbles is less significant than previously thought.
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