Ozone (O3) is a highly reactive molecule composed of three oxygen atoms. This unstable, energetic form of oxygen is a powerful oxidizing agent used widely for disinfection, such as purifying water and air. Its primary applications also include the oxidation of unwanted materials for odor removal and industrial processes. Because of its inherent instability, ozone cannot be stored or transported and must be created on-site for immediate use.
The Chemical Process of Ozone Formation
Creating ozone from standard diatomic oxygen (O2) requires a significant energy input to overcome the stability of the O2 molecule. High-energy sources, such as intense electrical discharge or ultraviolet radiation, are needed to break the double bond connecting the two oxygen atoms. This process splits a portion of the O2 molecules into individual, highly reactive free oxygen atoms (O).
These single oxygen atoms, or radicals, are unstable and rapidly combine with an intact O2 molecule to form the triatomic ozone molecule (O3). The net chemical reaction is inefficient, often requiring 10 to 20 times the theoretical energy for effective production. This energy input is necessary because ozone naturally and quickly reverts back to the more stable O2.
Technology Used in Ozone Generators
The two main commercial methods for producing ozone mimic natural phenomena like lightning and solar radiation. These devices control the energy input and oxygen source for efficient production. The choice of technology depends on the required ozone concentration and the specific application.
Corona Discharge (CD) Method
The Corona Discharge (CD) method is the most common technique for industrial and high-concentration applications, replicating the energy of a lightning strike. High voltage (typically 600 to 20,000 volts) is applied across a dielectric material, such as ceramic or glass, to create an electrical field. This field generates a silent, luminous electrical discharge, or “corona,” in the gap where oxygen flows.
The high-energy electrons within the corona split the O2 molecules into single oxygen atoms, which combine with other O2 molecules to form O3. Dielectric barriers, such as ceramic plates or tubular cells, spread the electron flow to maximize contact with the oxygen gas. While CD produces higher ozone concentrations, the high voltage and electrical discharge generate heat requiring cooling. It can also create undesirable byproducts like nitrogen oxides if the feed gas is not clean and dry.
Ultraviolet (UV) Light Method
Ozone can also be generated using specific wavelengths of ultraviolet (UV) radiation, mimicking the sun’s action in the Earth’s atmosphere. This method typically uses low-pressure mercury lamps that emit UV light at 185 nanometers (nm). The 185 nm wavelength has sufficient energy to photolyze, or split, the O2 molecule into two separate oxygen atoms.
These liberated oxygen atoms then react with other O2 molecules to form ozone. UV light also emits a germicidal wavelength of 254 nm, which destroys ozone, limiting the maximum concentration achievable. Consequently, UV generators are simpler, produce ozone at lower concentrations, and are often found in smaller-scale devices like air purifiers.
Safety Protocols for Ozone Generation
Ozone is a powerful oxidant, and its reactivity requires strict safety measures to protect human and animal health. Since ozone is a known respiratory irritant, the most important safety protocol is ensuring adequate ventilation where it is generated or applied. Proper air exchange accelerates the dissipation of residual ozone and prevents hazardous buildup.
High-concentration ozone treatments, such as shock deodorization, must be conducted only in non-occupancy settings, meaning no people or pets should be present. Continuous monitoring with ozone sensors is necessary, as the human sense of smell is unreliable due to rapid olfactory fatigue. Occupational standards, such as those set by OSHA, limit workplace exposure to 0.1 parts per million (ppm) for an eight-hour period.
Ozone is naturally unstable and breaks down into O2 over time, measured by its half-life. In air, ozone’s half-life ranges from four to twelve hours, depending on temperature and humidity. Where natural decomposition is too slow, specialized ozone destruct systems using heat or a catalyst actively convert the gas back to oxygen, ensuring safety before re-entry.