GETCO2: A Compact and Portable System for Automated Gas Transfer Velocity Measurements of Natural Waters

To enhance our understanding of surfactants in the exchange of climatically active gases across the water–atmosphere interface, we introduce a novel CO2 gas exchange tank equipped with a gas transfer velocity (kw) estimation tool, significantly improving upon earlier designs. This advanced platform integrates a commercially available, cost-effective, high-performance nondispersive infrared (NDIR) CO2 sensor with a closed controlled environment gas exchange tank. The tank is designed to induce precisely controlled water-side turbulence, allowing for the exploration of biological and chemical factors controlling the kw. The new system features a bespoke 3D-printed automated equilibrator, enabling precise measurements of the water CO2 concentration. CO2 concentrations in both air and water phases are measured using a novel setup that minimizes errors from sensor drift and incomplete mixing or equilibration. Measurement errors for equilibrated CO2 concentrations in air and water are 1.3 and 3.4%, respectively. The precision achieves kw values of 7.21 ± 0.18 cm h–1 with a coefficient of variation (CV) of 2.5% for deionized water. Testing with freshwater and marine waters yielded kw suppression levels comparable to an earlier automated gas exchange tank system utilizing gas chromatography. This next-generation GETCO2 system is smaller, easier to maintain, and more portable than previous models, allowing for wider-scale studies aimed at investigating the impact of surfactants and other organic compounds on kw suppression and enhancement across various natural water environments.