Air-Water Flux Reconciliation Between the Atmospheric CO₂ Profile and Mass Balance Techniques

Abstract

Studies deploying atmospheric flux-profile techniques in laboratory wind-wave tanks have been performed to demonstrate and verify the use of airside turbulent transport models and micrometeorological approaches to accurately determine air-water gas transfer velocities. Air-water gas transfer velocities have been estimated using the CO₂ atmospheric flux-profile technique in laboratory wind-wave tanks both at the NASA Wallops Flight Facility, USA and Kyoto University, Japan. Gas fluxes using the flux-profile and the waterside mass balance techniques have been reconciled. Air-water fluxes of H₂O and momentum were also measured simultaneously in a linear wind-wave tank. The waterside mass balances used the evasion of SF₆. The CO₂, H₂O, and momentum fluxes were calculated using the atmospheric flux-profile technique over a wind speed range of 1 to 14 m s⁻¹. The CO₂ and H₂O atmospheric profile model uses airside turbulent diffusivities derived from momentum fluxes. These studies demonstrate that the quantification of air-water CO₂ fluxes using the atmospheric flux-profile technique can be implemented in the laboratory. The profile technique can be used to measure an air-water flux in much less time than a mass balance. Effects of surfactants, wind speed, and wind stress on air-water transfer are also explored using the flux-profile technique. Validation of the air-water CO₂ gas exchange in laboratory wind-wave tanks provides evidence and support that this technique may be used in field studies.