Ozone is a particular gas present both in the Earth's upper atmosphere and at ground level. There are two distinct types of ozone; the Ground-level Ozone (or “bad” ozone) and the Stratospheric Ozone (or “good” ozone layer)
Ground-level Ozone (GOL) is located in the troposphere, close to the Earth's surface. It is the main ingredient of urban smog that originates in emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents. Ground level ozone is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ground-level ozone is a harmful pollutant for humans. Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion or it can worsen bronchitis, emphysema, and asthma. Another aspect of the GLO is its detrimental effect on the ecosystem as it can damage crops, trees and other vegetation. It is responsible for an estimated $500 million in reduced crop production each year in the United States.
The 1963 Clean Air Act (CAA) has set protective health-based standards for ozone. Amended several times since its creation, the CAA mandates the ongoing promulgation of a variety of emission standards and controls. Its primary objective is to establish Federal standards for various pollutants from both stationary and mobile sources and to provide for the regulation of polluting emissions via state implementation plans. In addition, the amendments are designed to prevent significant deterioration in certain areas where air quality exceeds national standards, and to provide for improved air quality in areas that do not meet Federal standards (referred to as "nonattainment" areas). The Environmental Protection Agency (EPA) and others organisms have also contributed to a variety of multi-faceted programs to meet health-based standards.
Figure 1: Location of the 2 ozone layers (EPA website)
Naturally produced in the stratosphere (extending upward from about 6 to 30 miles from the earth surface), the stratospheric ozone is a layer in the Earth atmosphere comparable to a natural shield protecting life on earth. This ozone absorbs between 97 to 99% of the sun’s harmful ultra-violet (UV) rays thus protecting life on earth. However, this "good" ozone is gradually being depleted by chemicals referred to as ozone-depleting substances (ODS), including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, and methyl chloroform. These man-made chemicals are ultimately responsible for more cases of skin cancer, cataracts, and other health problems.
In 1974 Mexican researcher Mario J. Molina and American F. S. Rowland published a laboratory study demonstrating the ability of CFC's to breakdown Ozone in the presence of high frequency UV light.
In 1985, atmospheric scientists highlighted the tremendous consequences of ozone-depleting substances for the ozone layer by pointing out the discovery of a “hole” in the upper atmosphere (stratosphere) over Antarctica.
Further studies estimated that the ozone layer would be depleted by CFC's by about 7% within 60 years. These incidents were soon followed by the signature by the US and 180 countries of the Montreal Protocol on Substances That Deplete the Ozone Layer, an international treaty designed to phase out the production of a number of substances believed to be responsible for ozone depletion. The treaty was opened for signature on September 16, 1987 and entered into force on January 1, 1989 and has been hailed as an example of international cooperation.
Figure2: Total reported global production of ozone depleting substances (ods). (2007). In UNEP/GRID-Arendal Maps and Graphics Library. Retrieved 17:03, March 26, 2008 from http://maps.grida.no/go/graphic/total-reported-global-production-of-ozone-depleting-substances
Since the adoption and strengthening of the Montreal Protocol has led to reductions in the emissions of CFCs, atmospheric concentrations of the most significant compounds have been declining. These substances are being gradually removed from the atmosphere. A complete recovery of the Antarctic ozone layer will not occur until the year 2050 or later. Although many countries have diligently complied with the Montreal Protocol allowing a drastic reduction of ozone depleting substances (see graph above), stockpiled, recycled and illegally traded CFCs, together with those in refrigeration and fire-fighting equipment, will still be around for many years.
While industrialized countries have agreed to phase out halocarbons, some critical uses are exempt and developing countries have been given longer time-scales.
Ozone depletion and climate change. (2007). In UNEP/GRID-Arendal Maps and Graphics Library. Retrieved 15:43, March 26, 2008 from http://maps.grida.no/go/graphic/ozone-depletion-and-climate-change (PDF file)
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