Stored grain products, such as corn, can harbor multiple microorganisms, including fungi such as Aspergillus species that produce toxins harmful to both humans and animals. In previous studies, we have demonstrated that ozone-treatment can significantly reduce the level of viable microorganisms on the surface of corn kernels. Ozone is a strong oxidizing agent, which is used in a growing number of industrial applications to control harmful microbes and volatiles. To achieve this goal, a better understanding of the properties of ozone is needed, especially with respect to the half-life of ozone and time/concentration criteria to reduce microbes on corn. The focus of this project was to determine the half-life time of ozone in air as a function of air speed (0 to 370 m3 /h), temperature (4 to 40°C) and relative humidity (0 to 80%) inside the cylinder. Half-Life Time (HLT) averaged ~1500 minutes in still air at room temperature (24°C) and zero humidity, which was substantially longer than previously published data (i.e., 30-40 minutes). As air speed, temperature and humidity increased, HLT decreased to ~40, 800 and 450 minutes, respectively. The results suggest that ozonation 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 flow rates of ozonated air at high temperature and humidity (e.g., grain storage silo in the middle of summer).