The halogen dioxide, chlorine dioxide is produced from its chlorite reactant using ion exchange media in a stable reactant form, and then passing a known concentration of counter ions through the ion exchange media in a moist environment so that there is an exchange of ions, and the reactants that are released form activated chlorine dioxide within the ion exchange material. The ion exchange media both contributes reactants to and extracts contaminants from the moist environment via its ion exchange mechanism. The counter ions may be derived from one or more stable precursor solutions which themselves may contain reactants and/or soluble catalysts. The reactants of the precursor solutions cannot act as the counter ion, or ions, in the ion exchange mechanism, but the soluble catalysts can. The ion exchange media can be mixed or layered with one or more insoluble catalysts, to enhance the formation of the activated halogen dioxide, chlorine dioxide within the ion exchange material.