A compact seawater pCO2 measurement system with membrane equilibrator and nondispersive infrared gas analyzer

A compact measurement system for partial pressure of CO2 in seawater (pCO2) with a membrane tube and a nondispersive infrared gas analyzer (NDIR) has been developed. Gaseous CO2 in seawater diffuses through the membrane into flowing air inside the tube, and the concentration of CO2 in the air is measured by NDIR. Equilibrium between the water and the air is achieved with a time constant of 2 minutes.pCO2 changes in seawater are monitored automatically and continuously with an uncertainty of ±5 μatm. Since the membrane equilibrator can be deployed directly in sea water, the system is small and requires only a small power supply. The system has wide application, not only in coastal zones but also in the open ocean or in incubators.