Ozone is an allotrope of oxygen. More than 90% of the ozone in the atmosphere is found in the ozone layer in the lower stratosphere, which is 15-50 km above the ground. There, oxygen molecules are broken down into oxygen atoms by the Sun’s high-energy radiation. Oxygen atoms then combine with oxygen molecules to form ozone. Ozone is vital to human survival and can absorb short-wave ultraviolet rays that are harmful to Earth life.
How was Ozone Discovered?
In 1785, Dutch chemist Martinus van Marum was conducting experiments when he noticed an unusual gas, but he didn’t realize it was ozone. Half a century later, GermanSwiss chemist Christian Friedrich Schonbein also noticed the same smell. He successfully separated the gaseous chemical and named it ozone (means “to smell” in Greek) in 1839. As a result, Schonbein is credited with discovery of ozone.
Ozone’s Physical Property
Ozone is a colorless or light blue gas at room temperature and pressure. It is slightly soluble in water and is easily soluble in carbon tetrachloride or fluorocarbons and turns the color blue. At -112℃, ozone gas will condense into dark blue liquid. At temperatures below -193℃, ozone gas will become purplish-black solid.
Ozone is a powerful oxidizing agent, which is highly unstable and will soon decay into ordinary diatomic oxygen even at high concentration. The half-life of ozone can be affected by temperature, humidity and air flow. Ozone has a pungent smell similar to chlorine bleach. People can sense the existence of ozone at the concentration of 0.01 μmol/mol in the air. Ozone at concentrations from 0.1 to 1 μmol/mol can cause headaches, eye burning and respiratory irritation in humans. Even a low concentration of ozone can to some extent cause damage to rubber materials, plastics and animals’ lungs.
Ozone’s Main Applications
The strong oxidizing property of ozone makes it widely applicable in many industries and applications. Ozone is mainly used for air and surface sterilization, odor removal, water treatment and a variety of advanced oxidation processes. When used for air and surface sterilization and odor removal, ozone can achieve the treatment of multiple environments in home, commercial, industrial, agricultural and other environments. Ozone also provides the best surface treatment solution for semiconductor industry. In water treatment, ozone is commonly adopted in drinking water sterilization, food processing water disinfection, swimming pool water treatment, aquaculture water treatment and decolorization, deodorization, detoxification in wastewater treatment.
Ozone’s Sterilization Principle
The sterilization principle of ozone belongs to biochemical oxidation reaction. When ozone is used for sterilization, ozone can directly oxidize the cell body of bacteria, so as to destroy its DNA and achieve the elimination purpose. Ozone can also inhibit the living of RNA in viruses. By oxidizing them, it can also significantly reduce the toxicity of many toxins.
Ozone Generation Methods
There are several ways to produce ozone gas. Based on their energy sources, the following are the 3 most popular ozone generation methods.
1. Corona Discharge
Corona discharge is the most widely applied and studied ozone generation method. Through a highvoltage discharge to oxygen or air, some of the oxygen molecules in the air will be broken down into oxygen atoms. Then, free oxygen atoms can combine with other oxygen molecules to form ozone molecules with three oxygen atoms, which is ozone.
2. Electrolysis of Water
In the process of water electrolysis, by providing an electric current into the water, a certain amount of oxygen in water can be converted into ozone. The electrolysis of water can produce a high concentration of ozone and eliminate the generation of nitrogen oxides. It is suitable for preparing ultrahigh purity ozonated water for pharmaceutical and electronic industry. But it has a higher economic cost than corona discharge method.
3. Ozone Generation from Ultraviolet
The ozone gas in the earth’s atmosphere is produced by the ultraviolet radiation from the Sun. Any ultraviolet radiation with a wavelength less than 200 nanometers can break down oxygen molecules into oxygen atoms. Oxygen atoms will then combine with oxygen molecules to form ozone. What is beneficial is that no nitrogen oxides will be produced in the process. But it has a lower efficiency, which means it is only suitable for the applications with a lower ozone yield requirements, such as small area sterilization and odor removal.
Is Ozone Safe?
In ozone’s countless applications, the safe use of ozone can be easily realized when the concentration of ozone is controlled and the sensitive articles (such as rubber, plastics, fabrics, paint and certain metals) within the space have been protected. Only in the case of longterm inhalation of a high concentration of ozone can ozone stimulate the human respiratory mucosa. The human olfactory system is extremely sensitive to ozone. People can easily sense the smell of ozone as long as its concentration reaches 0.02 PPM, which is far from the ozone safety standards in many countries.