Electrochemical Sensing System for Rapid In Situ Monitoring of Oceanic pCO2

Oceanic partial pressure of carbon dioxide (pCO2) monitoring is of great importance for fully understanding the inorganic carbon chemistry of seawater. However, the in situ determination of pCO2 via electrochemical sensing is still a challenge as a result of the fluctuating salinities and temperatures in a marine environment. In this work, a marine pCO2 monitoring system based on potentiometric sensing has been developed using real-time corrections for the salinity and temperature effects. The system consists of an electrochemical sensing unit based on an ion-selective electrode for selective carbonate detection, probes for seawater parameters (i.e., pH, salinity, and temperature), and a control system for autonomous sample analysis, sensor calibration, and pCO2 calculation. The proposed sensing device offers a response time of about 22 s (t95%), a detection accuracy of <2 μatm (mean deviation compared to the used standard CO2 gases), and a stability of 1.43% (mean relative standard deviation for the repeated measurements of the Tris–HCl buffer solutions equilibrated with different standard gases at pCO2 levels of 450, 600, and 800 μatm) for the real-time monitoring of pCO2. The functioning of the marine pCO2 monitoring system was validated via two different monitoring approaches (i.e., monitoring one site with a fixed duration and monitoring different sites in one sea region) in two different sea areas of China. The obtained results indicate the capability of the proposed pCO2 monitoring system to autonomously operate for routine in situ monitoring in terms of sampling, detection, calibration, data storage, and transmission. The proposed electrochemical sensing system can be used for submersible and shipboard monitoring of oceanic pCO2.