Ozone Background

Mentioning ozone to most people in the 1990s evokes the thought of the ozone hole discovered by NASA's Landsat spacecraft over the South Pole or unhealthy air over some of our nation's cities. In both instances, the thoughts accompany a negative connotation of pollution by man-made chlorinated fluorocarbons destroying the ozone layer or a by-product of the photolysis of automobile exhaust. History has been much more favorable recognizing the positive attributes of ozone, and other countries have embraced the application of ozone for its environmentally safe biocidal and deodorizing properties for more than a century (1).

Ozone has been a natural part of our environment well before recorded history and indeed has enabled man to live today protected from dangerous ultraviolet rays from the sun. Ozone is created naturally by lightning and photo-chemically by ultraviolet (UV) light. Electrical discharge and UV light breaks the naturally occurring oxygen molecule, 02, into two unstable atomic atoms, O, that can com bine with other oxygen molecules and form ozone, 03. Ozone produced by lightning is responsible for the fresh smell following a storm. If ozone were not formed in the upper atmosphere by 02 absorption of the sun's UV rays, the radiation would be able to reach the surface of the earth where it can cause skin cancer in humans and other negative effects on plants and animals.

From the early writings of Homer, man has observed the smell that accompanied lightning as "full of sulphur" odor (2). In 1785 a Dutch physicist, van Marum (3), observed ozone's characteristic odor when electrical sparks were passed through air. From the electrolysis of water, another process to produce ozone, Cruickshank (3) observed in 1801 the same odor near the anode. However, it was Schoenbein who is credited with the discovery of ozone (4). In a memoir presented to the Academy of Munich in 1840, Schoenbein concluded that the odor during electrical discharge and electrolysis and after a flash of lightning were the same substance. He named the substance ozone after the Greek word ozein meaning "to smell."

Ozone exists naturally at ground level in low concentrations. It dissipates rapidly by releasing one of the three oxygen atoms and reverting to common molecular oxygen. Thus, ozone's unstable property necessitates that it be manufactured on-site where it will be used. Today, for most practical applications, electrical discharges, UV radiation, and electrolysis are used to produce ozone. Electrical discharges produce the highest ozone gas concentrations efficiently, up to 80 g 03/kWh and up to 20% by weight in oxygen. UV radiation produces the lowest efficiencies, about 8 g 03/kWh (5). Electrolysis can produce ozone directly in water, eliminating the need to dissolve the ozone gas water.

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