Apollo SciTech's Underway pCO₂ system, model AS-P3, has been developed and tested for underway measurements (i.e., real-time while the vessel is sailing) of the partial pressure of CO₂ (pCO₂), pH, and dissolved oxygen (DO) in surface water, atmospheric CO₂ as well as water salinity, temperature, and position. Water sample is forced into the equilibrator by a shipboard pump. Equilibrated air is drawn from the equilibrator and dried with an electronic cooling system and a Nafion dry tube. It is then quantified with a CRDS CO₂ analyzer (Picarro G-2301), a laser-based CO₂ analyzer (LI-COR LI-7815), or an infrared CO₂ analyzer (LI-850 or LI-7000) before returning to the equilibrator. The shower-head equilibrator is effective (response time 2 min). The equilibrator is completely sealed from the outside room air.

It has been tested in both high (up to 3000 µatm) and low (less than 100 µatm) pCO₂ environments.