How Does Ozone Purify Air?
Effectiveness and Safety of Ozone

What Is Ozone?

Ozone is generated naturally by short-wave solar ultraviolet radiation and appears in our upper atmosphere (ozonosphere) in the form of a gas. Ozone also may be produced naturally by passing an electrical discharge -- such as lightning -- through oxygen molecules. Lightning is a perfect example of making an abundance of O3 to purify the earth's atmosphere Nature's way. Most of us have noticed the clean, fresh smell in the outdoor air after a thunderstorm, or the way clothing smells after it has been dried outside on a clothesline in the sun.

Here's how Ozone Molecules (O3) are converted from Oxygen (O2) as a result of an electrical charge: Oxygen, as we know, has two atoms. High voltage, as from lightning, breaks these two atoms apart. Quickly, these atoms hop back together in threes (O3). Confused, these atoms do not like this arrangement and want desperately to dissolve this uncomfortable trio.

So as this O3 molecule floats in the air, if one of the atoms spots a contaminant molecule, it breaks away from the other two atoms and attaches itself to the contaminant. This attachment is actually an attack on the contaminant (oxidation) and creates a microscopic explosion. Both the contaminant and the atom are destroyed. This leaves the other two atoms behind as pure oxygen {O2} without the presence of the contaminant. The explosion changes the contaminant into carbon dioxide and hydrogen, which we can breathe.

Ozone is highly reactive, so it interacts with most contaminates and allergens it encounters, rendering them harmless while also removing odors. Ozone can be effective against chemical sources, bacteria, mold, odors, etc. Once a pollutant is oxidized by ozone, it is no longer toxic, allergenic or odor causing. As a result, even if an oxidized contaminant remains in the air and is inhaled, it has no negative effect. Microorganisms such as mold spores or bacteria that have been exposed to ozone are no longer able to reproduce, which causes their numbers to quickly diminish. However, should the O3 molecule not find a contaminant in its environment, it will attack itself to change its configuration of O3 back to O2 (normal oxygen) in 20 to 30 minutes at room temperature and normal humidity.

"Ozone controls surface mold on packages and walls and reduces scale development and decay. The presence of ozone significantly reduces the occurrence of mold"

-- ASHRAE (American Society of Heating, Refrigeration and Air Conditioning)

How Else Does Ozone Purify?

Ozone is also biocidal, which means it kills harmful biological and bacterial contaminants. This biocidal action results from its reaction with the double bonds of fatty acids in bacterial cell walls, membranes and the protein capsid of viruses. In bacteria, the oxidation results in a change in cell permeability and leakage of cell contents into solution. Ozone attacks these cell walls, breaking down membranes and ultrastructural components of the organism. In more simple terms, the unstable electrons of ozone blast holes through the membranes. This occurs by cell lysing or rupturing the cell wall of viruses, bacteria, yeast and abnormal tissue cells, thereby destroying them by inactivation of the microorganism's enzymes. In viruses, alteration of the protein capsid prevents the virus from being taken up by susceptible cells.

Ozone displays an "all or nothing" effort in terms of destroying bacteria. It is such a strong germicide that only a few micrograms per liter are required to demonstrate germicidal action. Factors like humidity, temperature, pH, ozone concentration levels, type of organism and time, determine the kill rate for pathogens. The action of ozone gas in water is instantaneous. After oxidation, ozone returns to its original form of oxygen, without leaving any toxic by-products or residues.

Ozone oxidizes natural organic compounds like acetic and oxalic acids, as well as synthetic substances like nitro- and chloro-benzic compounds, detergents, herbicides and composite pesticides. Ozone oxidizes inorganics such as iron, manganese, heavy metals, cyanide, sulfides and nitrates in water.  Ozone retards the ripening of fruits and vegetables by destroying ethylene gas and bad odors, which are produced by aging and decay.

Ozone is more cost-effective than ethylene filters, which are costly and have to be replaced each month. Filters only act on the air that happens to pass through them, and ionization machines put a negative charge on air particles in the air which causes them to gravitate toward room surfaces. Unlike ozone, filters, ionizers and sprays do not eliminate the cause of odors. Once the cause has been eliminated, the odor does not come back unless the source that caused the odor is reintroduced.

Man-Made Ozone: Corona Discharge

The "lightning method" of ozone production has been duplicated commercially by many manufacturers of ozonating air purifiers and is known as corona discharge. In this method, 5,000 to 10,000 volts of electricity is used to split the O2 atoms to produce ozone. However, in addition to safety concerns and high operating costs, air purifiers utilizing the corona discharge method are plagued by unpredictable levels of ozone production -- ozone "blasts" -- and also produce undesirable and unhealthful byproducts such as nitric oxides. These oxides actually irritate the respiratory system -- not what you want in an air purifier. So in spite of claims that these units give you a "thunderstorm in a box," they have clear drawbacks.

Man-Made Ozone: Ultraviolet Light

Short-wave solar ultraviolet radiation -- ultraviolet light -- is another method used by many air purifier manufacturers. When ultraviolet light rays collide with a contaminant such as carbon monoxide (CO) and nitrogen oxides (NO2 and N2O) in the presence of oxygen (O2), ozone is produced.  

References

United States Environmental Protection Agency, Office of Air and Radiation, EPA Report 402-K-00-002, March 2000

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