Typical pCO2 systems that employ NDIR techniques are comprised
of sampling hardware, an analysis system, and a data logging
system. The analysis system includes an equilibrator (i.e., head
space unit), ancillary data collection equipment to measure temperature
and pressure, a sampling seawater supply and drain
line, condenser to remove moisture from the sample gases, and
a CO2 infra-red gas analyzer, IRGA (i.e., the handheld CEA GD
444±instrument). Similar to the head space unit (HSU) used in
this study an equilibrator ensures that the partial pressures of
CO2 in the water sample and head space gases are in equilibrium.
Other challenges encountered by scientists operating pCO2 systems
for ocean surfacepCO2 studies include temperature difference
between water intake and equilibrator and pressure changes in
the equilibrator resulting from unstable water flows. Such issues
should not be encountered with the head space unit because it
is implemented in close proximity to the system where DC is
being measured (