An experimental setup for the measurement of the contribution of air bubbles to gas exchange is presented. The bubble size distribution was measured as a function of the position in a 1.3m deep glass tank using an imaging method based on the depth from focus principle. Bubble radii from 100 to 1000 micro;m can be resolved with the recent image processing algorithm. The optical apparatus is automated to move horizontally and vertically along the tank walls in order to capture the whole bubble

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... ud. The bubble cloud is generated by a water jet which impinges on the water surface from above. The bubble distribution is similar to that produced by whitecaps, but stationary in a statistical sense. The flow rate of the air entrainment can be controlled. In a pilot experiment, the evasion of a set of trace gases was measured by means of UV absorption spectroscopy. The effect of the tracer solubility on the bubble-mediated gas exchange is demonstrated./p>