Half-life time of ozone as a function of air movement and conditions in a sealed container

• Evaluated the change in ozone concentration over time under varying air conditions.
• Developed a model to show the effect of these conditions on the HLT of ozone.
• Evaluated how such changes can affect the O3 levels during grain storage treatments.

The effectiveness of ozone sterilization of empty storage and transportation containers used for food products and bulk grains depend on the ability to maintain high concentrations over a sufficiently long period of time. The half-life time (HLT) is generally the measure used to characterize the degradation of a fumigant in air. It is typically affected by the air vapor properties, temperature and relative humidity, gas diffusivity and air tightness. The focus of this study was to determine HLT of ozone in air as a function of airflow (0, 0.028, 0.051, 0.10 m3/s), temperature (4, 24, 40 °C) and relative humidity (0, 30, 80%) in a sealed plexiglass cylinder equipped with a combination temperature/humidity sensor and fan. HLT was as high as 1524 min (25.4 h) in still air at 24 °C and zero humidity, which was substantially longer than previously published data (i.e., 30–40 min). As airflow, temperature and humidity increased, HLT decreased to as low as 39 min. The results suggest that sterilization with ozone will be more effective in still air at low temperature and humidity (e.g., headspace ozonation of rail cars in the early spring) than at high temperature and humidity (e.g., grain storage silo in the middle of summer).