The influence of intermittency on air/water gas transfer measurements

This paper theoretically investigates the influence of intermittency on determining average transfer velocities using different measuring techniques. It is shown that all measuring techniques can significantly be biased by intermittency. Mass balance and eddy correlation measurements are only biased when the concentration difference between the air and the water is spatially or temporally inhomogeneous over the measurement interval. Mean transfer velocities calculated either from mean boundary layer thicknesses or from thermographic techniques, which compute the mean transfer velocity either from concentration differences of from time constants, are biased toward lower values. The effects can be large and a simple stochastic bimodal model is used to estimate the effect.