The atomization of alkali halides in hydrogen/helium microwave induced plasma afterglows has been investigated in a fast-flow reactor using atomic absorption spectroscopy for the detection of metal atoms in the gas phase. By following the absorbance as a function of various experimental parameters, the atomization mechanism could be established and the rate-determining step derived. When the alkali halides are upstream of the plasma inlet only gas-phase atomization can occur in which the vaporization of the salt is the rate determining step. In the downstream position two atomization mechanisms can be active: at lower temperature, the lattice atomization mechanism is dominant. Heterogeneous interactions of hydrogen atoms with the salt lead to the formation of solid metal which thermal vaporization forms the rate-determining reaction. At higher temperature both lattice- and gas-phase atomization mechanisms can occur simultaneously.