Ultraviolet Radiation All energies that move at the speed of light are collectivelly referred to as electromagnetic radiation or 'light'. Various types of light differ in their wavelength, frequency and energy; higher energy waves have higher frequencies and shorter wavelengths. Pigments inside the retina of our eyes absorb wavelengths of light between 400nm-700nm, collectively referred to as 'visible light'. A "nm'' is a nanometer which is one billionth, or 10e-9, meters.
Stratospheric Oxygen and Ozone molecules absorb 97-99% of the sun's high freguency Ultraviolet light, light with wavelengths between 150 and 300nm. Ultraviolet-B(UV-B) is a section of the UV spectrum, with wavelengths between 270 and 320nm.
The amount of UV-B light recieved by a location is strongly dependent
on:
The
Cancer link The principle danger of skin cancer is to light-skinned
peoples. A 1%decrease in the ozone layer will cause a estimated
2%increase in UV-B irradiation; it is estimated that this will lead
to a 4%increase in basal carcinomas and 6%increase in squamous-cell
carcinomas.[Graedel&Crutzen]. 90% of the skin carcinomas are attributed
to UV-B exposure [Wayne] and the chemical mechanism by which it
causes skin cancer has been identified [Tevini]. The above named
carcinomas are relatively easy to treat, if detected in time, and
are rarely fatal. But the much more dangerous malignant melanoma
is not as well understood. There appears to be a correlation between
brief, high intensity exposures to UV and eventual appearance (as
long as 10-20yrs!) of melanoma. Twice as many deaths due to melanomas
are seen in the southern states of Texas and Florida, as in the
northern states of Wisconsin and Montana, but there could be many
other factors involved. One undisputed effect of long-term sun exposure
is the premature aging of the skin due to both UV-A, UV-B and UV-C.
Even careful tanning kills skin cells, damages DNA and causes permanent
changes in skin connective tissue which leads to wrinkle formation
in later life. There is no such thing as a safe tan.
Possible
eye damage can result from high doses of UV light,
particularly to the cornea which is a good absorber of UV light.
High doses of UV light can causes a temporary clouding of the cornea,
called 'snow-blindness', and chronic doses has been tenitively linked
to the formation of cataracts. Higher incidences of cataracts are
found at high elevations,Tibet and Bolivia; and higher incidences
are seen at lower latitudes(approaching the equator).
Damage to marine life The penetration of increased
amounts of UV-B light has caused great concern over the health of
marine plankton that densly populate the
top 2 meters of ocean water. The natural protective-responce of
most chlorophyll containing cells to increased light-radiation is
to produce more light-absorbing pigments but this protective responce
is not triggered by UV-B light. Another possible responce of plankton
is to sink deeper into the water but this reduces the amount of
visible light they need for photosynthesis, and thereby reduces
their growth and reproduction rate. In other words, the amount of
food and oxygen produced by plankton could be reduced by UV exposure
without killing individual organisms. There are several other considerations:
Author: Brien Sparling
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