Ozone in the stratosphere is created through chemical reactions between the sun's ultraviolet radiation and oxygen molecules. The common methods of artificial ozone generation are as follows:

1. Corona discharge: It is the most common and cost effective method of ozone generation. It works by means of a corona discharge tube or ozone plate. Using air for ozone generation produces nitrogen oxides in the process. This problem can be avoided by using oxygen for ozone generation, resulting in a higher concentration of ozone.

2. Ultraviolet: Ultraviolet ozone generator produces ozone by using ultraviolet light to illuminate the air. This method can only produce ozone at a concentration of about 0.5% or less. So, it has a low production rate. It can only be used for air treatment, not for water flow treatment. Its advantage is that no nitrogen oxides will be produced.

3. Cold plasma: In the cold plasma method, oxygen molecules will be split into individual atoms upon exposure. Ozone is formed by the recombination of the atoms. The advantage of this method lies in its high ozone production rate per unit time.

4. Electrolysis: The electrolysis method uses low voltage direct current through positive and negative electrodes to electrolyze deionized water to generate ozone. Electrolysis can achieve a high solubility of ozone in water. But the problems lie in its high energy consumption and short life of electrodes.

When ozone is produced, its amount in the air will continuously to fall as it will return to oxygen.
Ozone’s half-life: The half-life of ozone is about 30 minutes, meaning that half of the ozone generated will return to oxygen within 30 minutes. The process will constantly continue until all ozone gas returns to oxygen.
Reduction in chemical reaction: When ozone reacts with odors or fumes containing organic matter in the air, a certain amount of ozone in the air will be depleted in the reaction process.
Thermal decomposition: Ozone is more stable at low temperature than at higher temperature. A higher temperatures will make ozone break down faster.
As a result, ozone, although highly oxidizing, does not last very long after it is generated. It will soon return into oxygen when its oxidizing function is applied.