Gaseous chlorine dioxide (ClO₂) is one of the most promising air disinfectants. In this study, an ultra-low concentration of ClO₂ gas (< 1.2 mg/m³) was generated in an office at various levels of humidity and illuminance to investigate the decay law. The disinfection efficiency and metal corrosiveness of ultra-low concentrations of ClO₂ gas were also studied using an experimental chamber. At 48% and 75% humidity, the decay rate constants of ClO₂ gas were 0.0034 min⁻¹ and 0.0036 min⁻¹, respectively. The rate of decline of the ClO₂ concentration increased as the humidity of the environment increased. The decay rate constant of ClO₂ gas at an illuminance of 76 lux and 3429 lux was 0.0034 min⁻¹ and 0.00427 min⁻¹, respectively; hence, the decay rate increased with increased illumination. At a humidity of 72% and illuminance of 2112 lux, the decay rate constant reached 0.00880 min⁻¹. The effects of humidity and illuminance on the attenuation of the ClO₂ concentration were strongly synergistic. When the gas concentration was maintained below 0.9 mg/m³, the disinfection rate of ClO₂ on bacteria (P. aeruginosa, V. mimicus and S. aureus) exceeded 99.9%; thus, ClO₂ gas exhibited a high disinfection efficiency. In addition, there was no corrosion to various metals by ClO₂ under the same conditions. Consequently, gaseous ClO₂ at ultra-low concentrations has a high sterilization efficiency and is non-corrosive to metals.

Implications

Humidity and illuminance can influence decay laws of extremely low concentration ClO₂ gas. The gaseous ClO₂ at ultra-low concentrations has a high sterilisation efficiency and is non-corrosive to metals.