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 (k _w) 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 k _w. 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 k _w 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 k _w 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 k _w suppression and enhancement across various natural water environments.