Influence of CO2 and H2O on the air oxidation reaction of Mg nanoparticles has been investigated by Mg K-edge NEXAFS technique. The water vapor in the air causes rapid progression on the air oxidation reaction of the Mg nanoparticles. The basic magnesium carbonate (4(MgCO3).Mg(OH2).4(H2O) : BMC) is formed by the long term exposure to air. The NEXAFS analysis shows an existence of several intermediates of the BMC formation reaction.
