In 1840, a German chemist named Christian Friedrich Schoenbein was working in his  laboratory. The laboratory was poorly vented.  He noticed a pungent odor around some electrical equipment. He isolated the gas causing the odor and named it ozone from the Greek word that means "smell". Later, an Irish physical chemist named Thomas Andrews identified it as a form of oxygen. 
    Ozone, a three atom molecule of oxygen, is found in trace amounts in the air we breathe. Ozone in the upper atmosphere is mainly present in the ozone layer. At ground level it has been used in industry as air and water purifiers, as an aerobic digester of sewage and as a bleaching agent. Ozone was once thought to be beneficial in air conditioning. Now, ozone at ground level is considered a pollutant.
    Tropospheric ozone is a product of volatile organic compounds emitted from automobiles, chemical plants, dry cleaners, bakeries, evaporating gasoline, paints, solvents, etc. It also comes from nitrogen oxides emitted from automobiles, electric generating plants, small gasoline powered engines, and even trees.  It is not released from any specific source as other air pollutants are. The reactions that make ozone are more active on hot, sunny days.
    As it occurs naturally, near the earth's surface in the troposphere, O₃  is 20-30 ppb in country air and less in cities except where there is smog. In smog, O₃  is formed by sunlight acting upon O₂  in the air in the presence of impurities.  On heavy smog days (Ozone Alert Days) concentrations may reach 500 ppb or more for short periods of time. It is a main component of urban smog. If it is in high enough concentrations it has toxic effects on plants and animals. As long ago as 1979, the EPA recognized the need for air quality standards on ozone levels and established an upper limit for ozone at 120 ppb for an average over a one hour period. These upper limits may be changed by the EPA. In fact discussions are occurring that the upper limit is currently too high and may be lowered as much as 80 ppb over eight  hours.
    In the stratosphere ozone is formed naturally by short wavelength UV radiation. O₂  dissociates into 0 atoms in the presence of wavelengths less than ~200 nanometers. The O atoms combine with other oxygen molecules to make ozone. When exposed to wavelengths ranging from 200-400 nanometers, ozone is destroyed.
    Ozone in the stratosphere is beneficial to living organisms since it helps filter out UV rays from the sun.  This leads to the paradox of "good" ozone versus "bad" ozone. When ozone levels increase in the troposphere, breathing is especially difficult for older persons, asthma patients, and people who exercise outdoors. It is the same ozone that is good for us if it is in the stratosphere since it protects us, but  bad for us at lower levels in the atmosphere since it reacts adversely with eyes and lungs. An interesting correlation between tropospheric and stratospheric ozone is that a decrease of stratospheric ozone leads to an increase of tropospheric ozone because more UVB radiation  reaches the earth thus helping to create more ozone at ground level.
    Ozone is found in irregular quantities over the earth.  It is generally thinner over the equator  than over the poles. Its thickness varies depending upon solar intensity and atmospheric conditions that constantly change.
    A number of studies are currently being done on both tropospheric and stratospheric levels of  ozone. Some compare atmospheric conditions. The TOL module (project) includes many atmospheric conditions and analysis capabilities that make it unique. Questions have arisen about why ozone levels have varied so much within the same testing sites. Do atmospheric conditions effect ozone concentrations?  If so, which ones effect the concentrations of ozone?
    Ozone reacts with a number of agents. Ozone reacts with potassium iodide to release the iodine. It also reacts with colored organic materials such as indigo and litmus to destroy color. (Remember that it is sometimes used as a bleach?)  It reacts with mercury to form a thin skin of mercurous oxide that causes the mercury to cling to the inside of its container. It reacts with  tetramethyl- diaminodiphenylmethane in alcohol solution with a trace of acetic acid to form a violet color (hydrogen peroxide-colorless, chlorine or bromine-blue, nitrogen tetroxide-yellow).
    Testing for ozone usually depends upon its ability to react to various substances. Examples of this type of testing is the Drager tube, the Ecobadge and the Schoenbein paper.  Its ability to alter substances makes the testing with TERC Rubber-Thread Ozonometer possible.
    Ozone also prevents some plants from being able to store starches and therefore stunts their growth. Ozone lessens some plants, including some trees, ability to fight diseases.  It damages other plants, including milkweed. This makes the testing of plants a possible method for determining ozone levels.

For further information on testing techniques and ozone, refer to the Testing Methodology and/or Ozone Related Sites sections in this document. Much of the information in this portion of the TOL document can be found in the links.
 
 
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