New light on mechanism of air-water oxygen exchange in quiescent systems

Experiments employing novel apparatus which permits measurement of the rate of oxygen transport across liquid strata indicate that the diffusivity of oxygen through water immediately adjacent to the free air-water interface of a quiescent system is the same as its molecular diffusivity in bulk water remote from an interface. A molecular diffusivity of 2.07 × 10 −5 cm 2 s −1 is reported. Water strata of thickness ranging from 0.3 to 3.6 mm are shown to be effectively isotropic with respect to their resistance to oxygen transport. Thicker strata were found to exhibit a reduced but significant resistance consistent with the spontaneous development of a mechanically disturbed bulk zone between the boundary layers.