Ship-based pCO2 underway system provides CO2 mixing ratio data for near-surface water that can be used to calculate seawater CO2 partial pressure (pCO2)

The sensor operates through rapid diffusion of dissolved gas from water through a semi-permeable membrane to a non-dispersive infrared (NDIR) gas analyzer. The sensor was factory calibrated (February 2020) prior to deployment on the RV William Kennedy using gas traceable to international standards at the NOAA ESRL GMD Central Calibration Laboratory. Declared accuracy is 0.01 ppm or ± 0.5%. Long-term stability is achieved through an automated zeroing routine that periodically removes CO2 from the system establishing a new zero CO2 baseline value. Seawater was continuously pumped through the system at a rate of approximately 1 L/min from a clean water intake located approximately 2 m beneath the surface aboard the RV William Kennedy. Through sensor programing the pCO2 was sampled at ~7 min increments during the 2021 James Bay expedition.