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It is divided into four sections: Some of the materials presented in this document are subject to periodic revision by EPA. Updated versions of these documents may be obtained by writing to: Ozone is a form of molecular oxygen that consists of three oxygen atoms linked together.
Ozone in the upper atmosphere the "ozone layer" occurs naturally and protects life on earth by filtering out ultraviolet radiation from the sun.
Ozone at ground level, however, is highly corrosive, damaging plant, animal, and human tissue, and other materials such as metals and masonry. It is the major component of urban smog. Why is Ozone a Public Health Problem? Ozone is a severe irritant.
It is responsible for the choking, coughing, and stinging eyes associated with smog. Ozone damages lung tissue, aggravates respiratory disease, and makes people more susceptible to respiratory 113744 essay.
Children are especially vulnerable to ozone's harmful effects, as are adults with existing disease. But even otherwise healthy individuals may experience impaired health from breathing ozone-polluted air.
Elevated ozone levels also inhibit plant growth and can cause widespread damage to crops and forests. The standard is based on the highest ozone exposure sensitive persons can tolerate.
See list of Ozone Classifications later in this section. How is Ozone Formed? Ozone is not emitted directly but is formed in the atmosphere through a complex set of chemical reactions involving hydrocarbons HC and oxides of nitrogen NOx catalyzed by sunlight.
The rate at which these reactions occur is affected by both temperature and intensity of the sunlight. For this reason, high ozone levels occur most often on hot summer afternoons.
Hydrocarbons and nitrogen oxides come from a wide variety of industrial and combustion processes. In typical urban areas, one-third to one-half or more of those pollutants come from cars, trucks, and buses.
How is Ozone Monitored? Pollutant concentrations are continually measured by networks of national, state and local monitoring stations. Most monitoring stations are situated in urbanized areas to measure ozone concentrations to which the population is exposed but some are located in down-wind areas as well.
Ozone measurements are averaged over a one-hour period and compared to the standard of 0.
Violations of the ozone standard are determined by looking at the second highest daily readings obtained from the monitoring sites in an urbanized area hi a year. Hence, more than one day of high ozone readings is needed in order for an area to be in violation of the ambient ozone standard.
An area meets the ozone standard if, on average, not more than one annual exceedance is recorded over a three year period. Since then, seven areas have been redesignated to attainment based upon a lack of violations over a three year period and a demonstration that the air quality improvements can be maintained over time.
Resignations are pending in several other areas as well see lists later in this section. Ozone is usually not formed at the point where the precursors, hydrocarbons and oxides of nitrogen, are emitted.
Rather, these chemicals are typically carried some distance on the wind before the right mix and conditions for ozone formation are achieved. Pollutants in one area can contribute to ozone problems in other areas.Free Essay: 1.
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