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Sun Safety
All life on Earth depends in part on a thin shell of gaseous
layer of ozone that
stretches from about 15 to 50 kilometers above us and covers the planet like an
invisible, protective shield. The ozone layer is the main barrier between us and
the hazardous ultraviolet radiation that constantly comes toward the Earth from
the burning surface of the Sun. Ozone screens out only the more energetic
ultraviolet rays while allowing the visible light and the warm infrared to pass
through untouched, causing harm to our bodies.
Ozone Deplition
Ozone is a molecule composed of three
oxygen atoms, designated by the chemical symbol O3. Although ozone is
found in small amounts at all altitudes in the atmosphere, due to
chemical, dynamical, and radiative processes it is not evenly
distributed. Approximately 90 percent of all ozone is contained in the
region of the atmosphere known as the stratosphere, which lies between
15 and 50 km above the Earth's surface. The region below the
stratosphere where our weather takes place is known as the troposphere.
The ozone depletion
process begins when CFCs
and other ozone-depleting
substances (ODS) are emitted into the atmosphere. Winds efficiently mix
the troposphere and
evenly distribute the gases. CFCs are extremely stable, and they do not dissolve
in rain. After a period of several years, ODS molecules reach the stratosphere,
Strong UV light breaks
apart the ODS molecule. CFCs, HCFCs, carbon tetrachloride, methyl chloroform,
and otehr gases release chlorine atoms, and halons and methyl
bromide release bromine atoms . It is these atoms that actually destroy ozone,
not the intact ODS molecule. It is estimated that one chlorine atom can destroy
over 100,000 ozone molecules before it is finally being removed from the
stratosphere
Ozone is constantly produced and destroyed in a natural cycle,
however the overall amount of ozone
is essentially stable. This balance can be thought of as a stream's depth at a
particular location. Although individual water molecules are moving past the
observer, the total depeth remains constant. Similarly, while ozone production
and destruction are balanced, ozone levels remain stable. This was the situation
until the past several decades.
Large increases in stratospheric chlorine and bromine, however, have upset
that balance. In effect, they have added a siphon downstream, removing ozone
faster than natural ozone creation reactions can keep up. Therefore, ozone
levels fall.
Since ozone filters out harmful UVB
radiation, less ozone
means higher UVB levels at the surface. The more depletion, the larger the
increase in incoming UVB. UVB has been linked to skin cancer, cataracts, damage
to materials like plastics, and harm to certain crops and marine organisms.
Although some UVB reaches the surface even without ozone depletion, its harmful effects will
increase as a result of this problem.
Chlorofluorocarbon (CFC):
CFCs are very stable in the troposphere. They move to the Stratosphere and
are broken down by strong ultraviolet light, where they release chlorine atoms
that then deplete the ozone layer. CFCs are commonly used
as refrigerants, solvents, and foam blowing agents. The most common CFCs are CFC-11,
CFC-12, CFC-113, CFC-114, and CFC-115.
Ozone-Depleting Substance(s) (ODS):
ODS include CFCs, HCFCs, halons, methyl bromide,
carbon tetrachloride, and methyl chloroform. ODS are
generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down,
they release chlorine or bromine atoms, which then deplete ozone.
UV: ultraviolet radiation
Ultraviolet radiation is a portion of the electromagnetic spectrum with
wavelengths shorter than visible light. The sun produces UV, which is commonly
split into three bands: UVA, UVB, and UVC. UVA is not absorbed by ozone. UVB
is mostly absorbed by ozone, although some reaches the Earth. UVC is completely
absorbed by ozone and normal oxygen.
UVB is a kind of ultraviolet light from the sun (and sun lamps) that has several harmful effects.particularly
effective at damaging DNA. It is a cause of melanoma and other types of skin
cancer. It has also been linked to damage to some materials, crops, and marine
organisms. The ozone layer protects the Earth against most
UVB coming from the sun. It is always important to protect oneself against UVB,
even in the absence of ozone depletion, by wearing hats,
sunglasses, and sunscreen. However, these precautions will become more important
as ozone depletion worsens
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