The Pacific Marine Environmental Laboratory’s underway pCO2 system measures the partial pressure of CO2 in the air and surface water while the ship is underway. The pCO2 values, along with temperature and salinity data from the shipboard TSG are used to calculate the flux of CO2 at the air-sea interface. The system determines CO2 content with a Licor infrared detector and is calibrated with 4 gas cylinders provided by the Earth System Research Laboratory.