On the parameters influencing air‐water gas exchange

TLDR

The study measured gas exchange in two circular and one linear wind/wave tunnels using tracers such as heat, He, CH₄, CO₂, Kr, and Xe. Experiments reveal that waves dominate water‑side transfer, shifting the Schmidt number scaling from k∝Sc^−2/3 to k∝Sc^−1/2, with wind‑generated wave energy boosting near‑surface turbulence, and that the mean square wave slope best predicts transfer rates.

Abstract

Detailed gas exchange measurements from two circular and one linear wind/wave tunnels are presented. Heat, He, CH 4 , CO 2 , Kr, and Xe have been used as tracers. The experiments show the central importance of waves for the water‐side transfer process. With the onset of waves the Schmidt number dependence of the transfer velocity k changes from k ∝ Sc −⅔ to k ∝ Sc −½ indicating a change in the boundary conditions at the surface. Moreover, energy put into the wave field by wind is transferred to near‐surface turbulence enhancing gas transfer. The data show that the mean square slope of the waves is the best parameter to characterize the free wavy surface with respect to water‐side transfer processes.