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Ozone
http://www.stateoftheair.org/2009/states/michigan/ Ozone occurs in two layers of the
atmosphere. The layer closest to the Earth's surface is the troposphere.
Here, ground-level or "bad" ozone is an air pollutant that is
harmful to breathe and it damages crops, trees and other vegetation. It is a
main ingredient of urban smog. The troposphere generally extends to a level
about 6 miles up, where it meets the second layer, the stratosphere. The
stratosphere extends upward from about 6 to 30 miles. The stratospheric or
"good" ozone protects life on Earth from the sun's harmful
ultraviolet (UV) rays. The highest levels of ozone in the atmosphere are in the
stratosphere, in a region also known as the ozone layer between about
10 km and 50 km above the surface (or between about 6 and 31
miles). Here it filters out photons with shorter wavelengths (less than
320 nm) of ultraviolet light, also called UV rays, (270 to 400 nm)
from the Sun that would be harmful to most forms of life in large doses.
These same wavelengths are also among those responsible for the production of
vitamin D, a vitamin also produced by the human body. Ozone in the
stratosphere is mostly produced from ultraviolet rays reacting with oxygen: O2 + photon →
2 O O + O2 → O3 It is destroyed by the reaction with atomic oxygen: O3 + O → 2 O2 Ozone is produced naturally in the stratosphere. But this
"good" ozone is gradually being destroyed by man-made chemicals
referred to as ozone-depleting substances (ODS), including
chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl
bromide, carbon tetrachloride, and methyl chloroform. These substances were
formerly used and sometimes still are used in coolants, foaming agents, fire
extinguishers, solvents, pesticides, and aerosol propellants. Once released
into the air these ozone-depleting substances degrade very slowly. In fact,
they can remain intact for years as they move through the troposphere until
they reach the stratosphere. There they are broken down by the intensity of
the sun's UV rays and release chlorine and bromine molecules, which destroy
the "good" ozone. Scientists estimate that one chlorine atom can
destroy 100,000 "good" ozone molecules. Even though we have reduced or eliminated the use of many ODSs, their use
in the past can still affect the protective ozone layer. Research indicates
that depletion of the "good" ozone layer is being reduced
worldwide. Thinning of the protective ozone layer can be observed using
satellite measurements, particularly over the Polar Regions. Ozone depletion can cause increased amounts of UV radiation to reach the
Earth which can lead to more cases of skin cancer, cataracts, and impaired
immune systems. Overexposure to UV is believed to be contributing to the
increase in melanoma, the most fatal of all skin cancers. Since 1990, the
risk of developing melanoma has more than doubled. UV can also damage sensitive crops, such as soybeans, and reduce crop
yields. Some scientists suggest that marine phytoplankton, which are the base
of the ocean food chain, are already under stress from UV radiation. This
stress could have adverse consequences for human food supplies from the
oceans. The United States, along with over 180 other countries, recognized the
threats posed by ozone depletion and in 1987 adopted a treaty called the
Montreal Protocol to phase out the production and use of
ozone-depleting substances. The largest use of ozone is in the preparation of pharmaceuticals,
synthetic lubricants, as well as many other commercially useful organic
compounds, where it is used to sever carbon-carbon bonds. It can also be used
for bleaching substances and for killing microorganisms in air and water
sources. Many municipal drinking water systems kill bacteria with ozone
instead of the more common chlorine. Ozone has a very high oxidation
potential. Ozone does not form organochlorine compounds, nor does it remain
in the water after treatment. The Safe Drinking Water Act mandate that these
systems introduce an amount of chlorine to maintain a minimum of 0.2 ppm
residual Free Chlorine in the pipes, based on results of regular testing.
Where electrical power is abundant, ozone is a cost-effective method of
treating water, since it is produced on demand and does not require
transportation and storage of hazardous chemicals. Once the ozone has decayed, it leaves no taste or odor in drinking
water. Although low levels of ozone have been advertised to be of some
disinfectant use in residential homes, the concentration of ozone in dry air
required to have a rapid, substantial effect on airborne pathogens exceeds
safe levels recommended by the U.S. Occupational Safety and Health
Administration and Environmental Protection Agency. Humidity control can
vastly improve both the killing power of the ozone and the rate at which it
decays back to oxygen (more humidity allows more effectiveness). Spore forms
of most pathogens are very tolerant of atmospheric ozone in concentrations
where asthma patients start to have issues. Industrially, ozone is used to: Disinfect laundry in hospitals, food factories, care homes etc; Disinfect water in place of chlorine Deodorize air and objects, such as after a fire. This process is extensively
used in Fabric Restoration Kill bacteria on food or on contact surfaces; Sanitize swimming pools and spas Kill insects in stored grain Scrub yeast and mold spores from the air in food processing plants; Wash fresh fruits and vegetables to kill yeast, mold and bacteria; Chemically attack contaminants in water (iron, arsenic, hydrogen
sulfide, nitrites, and complex organics lumped together as
"color"); Provide an aid to flocculation (agglomeration of molecules, which
aids in filtration, where the iron and arsenic are removed); Manufacture chemical compounds via chemical synthesis Clean and bleach fabrics (the former use is utilized in Fabric
Restoration; the latter use is patented); Assist in processing plastics to allow adhesion of inks; Age rubber samples to determine the useful life of a batch of rubber;
Eradicate water borne parasites such as Giardia lamblia and
Cryptosporidium in surface water treatment plants. Many hospitals in the U.S. and around the world use large ozone
generators to decontaminate operating rooms between surgeries. The rooms are
cleaned and then sealed airtight before being filled with ozone which
effectively kills or neutralizes all remaining bacteria. Ozone is used as an alternative to chlorine or chlorine dioxide in
the bleaching of wood pulp. It is often used in conjunction with oxygen and
hydrogen peroxide to eliminate the need for chlorine-containing compounds in
the manufacture of high-quality, white paper Ozone can be used to detoxify cyanide wastes (for example from gold
and silver mining) by oxidizing cyanide to cyanate and eventually to carbon
dioxide. Devices generating high levels of ozone, some of which use
ionization, are used to sanitize and deodorize uninhabited buildings, rooms,
ductwork, woodsheds, and boats and other vehicles.
Breathing ozone can trigger a variety of health problems including chest pain,
coughing, throat irritation, and congestion. It can worsen bronchitis,
emphysema, and asthma. Ground-level ozone also can reduce lung function and
inflame the linings of the lungs. Repeated exposure may permanently scar lung
tissue. Ground-level ozone also damages vegetation and ecosystems. In the United
States alone, ozone is responsible for an estimated $500 million in reduced
crop production each year. Under the Clean Air Act, EPA has set protective health-based standards
for ozone in the air we breathe. EPA and others have instituted a variety of
multi-faceted programs to meet these health-based standards |
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