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What is UV Radiation?
The sun emits radiation
of different wavelengths. Some of the radiation, such as those making up the colours of rainbow, have wavelengths
to which our eyes respond.
Beynod these wavelengths are radiation in the ultraviolet (UV) and infrared which our eyes cannot see.
UV radiation is of concern to us because unprotected exposure to it can cause skin and
eye damage. UV radiation can be broadly subdivided into UV-A, UV-B and UV-C. Their main characteristics
are shown in Table 1.
| |
UV-A
|
UV-B
|
UV-C
|
|
Wavelength
(nanometer, nm)*
|
315-400 |
280-315 |
100-280 |
|
|
Penetrates the ozone layer |
Mostly absorbed by the ozone layer |
Almost all absorbed by the ozone layer |
|
Amount reaching the Earth's surface
|
> 98% of UV radiation is UV-A |
< 2% of UV radiation is UV-B |
Negligible
|
*Definition based on International Commission on
Illumination (CIE).
(1nm=10-9m)
Table 1 : Main characteristics of UV-A, UV-B and UV-C radiation
UV Radiation can generate photochemical
smog. Overexposure in
human can induce skin and eye injury, photokeratoconjunctivitis, eye cataract
and skin cancer.
Factors affecting the ground-level UV
intensity
| |
Factor |
Influence on UV intensity at
the Earth's surface |
 |
Position of the sun which varies with time of
the year, time of the day and the latitude. |
The higher the sun's position, the higher the
UV intensity. |
 |
Amount of ozone in the atmosphere. |
Ozone absorbs UV radiation. The more abundant
the ozone in the atmosphere, the less the amount of UV radiation reaching
the Earth's surface. |
 |
Clouds and haze. |
UV radiation is both absorbed and scattered
by clouds and haze. |
 |
Ground reflection. |
Most natural surfaces such as grass, soil and
water reflect less than 10% of UV. However, fresh snow strongly reflects
(80%) UV. Sand also reflects 10-25% of UV. |
 |
Altitude above the sea level. |
The higher the altitude, the higher the UV intensity
as the depth of the atmosphere and therefore the amount of ozone available
to absorb UV radiation is reduced. |
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