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Ozone Generation

Ozone is the triatomic state of oxygen, that is, it is a molecule comprising of three oxygen atoms having the chemical symbol O3. In 1856 Thomas Andrews showed that ozone was formed only by oxygen, and in 1863 Soret established the relationship between oxygen and ozone by finding that three volumes of oxygen produce two volumes of ozone.

Ozone formation is endothermic. Ozone is thermodynamically is unstable and spontaneously reverts back into oxygen.

In the Earth’s stratosphere, the ozone generation occurs naturally (with concentrations between 5 and 10 ppm), protecting the planet and its inhabitants by absorbing ultraviolet radiation of wavelength 290-320 nm (Ullmann’s, 1991).

Resonance Structures of Ozone

Ozone (O3), or trioxygen, is a triatomic molecule consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope (O2), breaking down with a half life of about half an hour in the lower atmosphere to O2. Ozone is diamagnetic, which means that its electrons are all paired. In contrast, O2 is paramagnetic, containing two unpaired electrons.

According to experimental evidence from microwave spectroscopy, ozone is a bent molecule, with C2v symmetry (similar to the water molecule). The O – O distances are 127.2 pm (1.272 Å). The O – O – O angle is 116.78°. The central atom is sp² hybridized with one lone pair.

Ozone is a polar molecule with a dipole moment of 0.53 D. The molecule can be represented as a hybrid resonance with two contributing structures, each with a single bond on one side and double bond on the other. The arrangement possesses an overall bond order of 1.5 for both sides.

Ozone is naturally produced in Nature

In Nature we can find Ozone in the stratosphere and in the troposphere levels. Ozone generation is produced naturally in the upper atmosphere (Stratosphere) through ultraviolet radiation creating the ozone layer that absorbs 9990 harmful ultraviolet radiations from the sun. As well, lightning will produce Ozone through electrical excitation of Oxygen molecules. Oxygen is very stable, but can be separated into separate molecules by excessive energy. An oxygen molecule is very reactive, hence the term oxidization.

In stratosphere ozone is formed and dissociated reversibly. Ozone generation happens in nature by lightning and can be smelled after a storm. It is one of nature’s most powerful oxidizers. Ozone generation is done by converting Oxygen (O2) into Ozone (O3). Oxidizers are a class of chemicals that break down organic substances.


Ozone production by lightning

During a strike of lighting, electrons move up and down the path created until the charge has been neutralized. This creates a lot of heat and vacuums to develop in the atmosphere which collapses afterwards, hence the shock-wave we hear as thunder. Therefore the oxygen molecules are quite reactive and can rebind into ozone instead of oxygen under these conditions.

Ultraviolet Radiation

Ozone production by ultraviolet radiation

UV light in the range from 160 – 240 nm will create ozone from oxygen.Ultraviolet radiation from the sun strikes a diatomic oxygen molecule and splits it into two oxygen atoms. Ozone is created by the photolysis of the oxygen molecule (O2). This will disrupt the molecule and create oxygen atoms (O) that will then attach to any individual oxygen molecules (O2) to create ozone (O3).

How can Ozone be Man-Made?

Ozone cannot be stored, so ozone must be generated on-site and must be used as quickly as it is produced.
Besides its natural occurrence in the nature, Ozone can be produced by ozone generators.

Corona Discharge

Descarga Corona ozone generator, a powerful tool for ozone therapy and disinfection.

Coronal discharge is the most common type of ozone generator for most industrial and personal uses. While variations of the “hot spark” coronal discharge method of ozone production exist, including medical grade and industrial grade ozone generators, these units usually work by means of a corona discharge tube. They are typically cost-effective and do not require an oxygen source other than the ambient air to produce ozone concentrations of 3–6%. Fluctuations in ambient air, due to weather or other environmental conditions, cause variability in ozone production. However, they can also use an air dryer (to reduce or eliminate nitric acid formation by removing water vapor and increase ozone production) or an oxygen concentrator (to increase the ozone production and further reduce the risk of nitric acid formation by removing not only the water vapor, but also the bulk of the nitrogen).

Ultraviolet Light

UV, an ozone generator used for ozone therapy and disinfection.

UV ozone generators, or vacuum-ultraviolet (VUV) ozone generators, employ a light source that generates a narrow-band ultraviolet light, a subset of that produced by the Sun. UV ozone generators utilize UV light at 185-nanometer wavelength that shine on feed gas flowing through a suitable tube chamber.
UV ozone generators use ambient air for ozone production, no air dryer or oxygen concentrator are used, therefore these generators tend to be less expensive. However UV ozone generators usually produce ozone with a low concentration which limits the potential ozone production rate. Another disadvantage of this method is that it requires the ambient air (oxygen) to be exposed to the UV source for a longer amount of time, and any gas that is not exposed to the UV source will not be treated. UV lamps solarize over time, requiring periodic replacement.