Effects of various indoor environmental factors on the decay of chlorine dioxide gas concentration: Implications of its use against pandemic influenza

Air-cleaning systems using a low concentration of chlorine dioxide (ClO ₂) gas for prevention against infection by the influenza virus have been developed. ClO ₂ gas is easily decomposed by indoor climate factors. Three experiments were conducted to evaluate the effects of indoor environmental factors on the decrease of ClO ₂ gas concentration. The reaction (decay) rate constant was also determined. High air temperatures and light irradiation accelerated the decrease of ClO ₂ gas concentration; the latter had the greatest influence on the decrease of ClO ₂ gas concentration among the conditions. A quicker decay of concentration and greater value of the reaction rate constant of ClO ₂ was found when a UV lamp was used; this is because the gas absorbs irradiation in the UV range. ClO ₂ gas concentration was significantly reduced when an evaporative humidifier was employed due to adsorption and a chemical reaction between the gas and the filter in the humidifier.