Why must ozone be generated on site?

Ozone must be generated on site primarily because it is an unstable gas that begins to decompose almost immediately after it is created. This instability limits its shelf life; ozone is best used shortly after generation to ensure its effectiveness as a disinfectant and oxidant in water treatment processes. By generating ozone on site, facilities can produce it fresh and use it immediately for applications such as disinfection, taste and odor removal, and oxidation of contaminants.

The other options, while related to the logistics and properties of ozone, do not directly address the reason for on-site generation. Though ozone can be expensive to transport, the immediate concern is its degradation over time. Additionally, ozone is effective even in small quantities, and while it does decompose quickly, the primary concern remains its instability which dictates the need for on-site production to maximize its efficacy in treatment applications.