Carbon Dioxide Concentration

Mole fraction of carbon dioxide (xCO2) in sea water near the ocean surface in units of micromoles per mole (µmol/mol). For instance, an xCO2 of 400 µmol/mol indicates that a mole of sea water contains 400 micromoles of CO2, or 400 millionths of a mole, or 0.0004 mole.