UV radiation monitoring: UV index and UV dose
UV radiationElectromagnetic radiation or "light" is the collective name for all forms of energy that move with the speed of light. There are different "types of light" in the spectrum, depending on their energy, which is related to the wavelength (freqency) of the light: the lower the wavelength, the higher the energy.
The human eye is sensitive for only a part of the spectrum, referred to as "visible light": between 400 and 780 nm (1 nm = 10-9 meter). The wavelength of the light determines the colour: 400 nm is blue, 700 nm is red.
The part of the spectrum immediately to the left of blue, between 200 and 400 nm is the ultraviolet light (UV). The UV is usually divided into three components, with increasing energy:
The UV-C energy is potentially more dangerous, but it decreases dramatically as ozone increases, because of the strong absorption in the 200-280 nm wavelength band. The UV-B is also strongly absorbed, but a small fraction reaches the surface. The UV-A is only weakly absorbed by ozone, with some scattering of radiation near the surface.
Atmospheric ozone thus shields life at the surface from most of the harmful components of the solar UV radiation. Chemical processes in the atmosphere can effect the level of protection provided by the ozone in the upper atmosphere.
Ozone decline in the stratosphere can be caused by:
It is therefore important to monitor the UV radiation that reaches the ground. One of the tools for this is the UV index.
Note on the UV-A & UV-B wavelength rangesThe wavelength of the devision between UV-A and UV-B varies in the literature and this may lead to some confusion.
The Commission Internationale de l'Éclairage (International Commission on Illumination) uses 280-315 nm as UV-B and 315-400 nm as UV-A.
Other sources put the devision point at 320 nm, as in the above given definition. In particular this is done in medical (dermatological) applications, as well as in cosmetics. Also several text books on UV use 320 as devision point.
To avoid confusion, one could use the following short-hand notation: dUVB for 290-320 nm and dUVA for 320-400 nm, where "d" stands for dermatological, and use UVA and UVB for the 315-nm devision quantities. The use of the prefix "d" is not very common, though.
Within the TEMIS project, the data supplied are the UV index and UV dose, which cover (parts of) both UV-A and UV-B. The precise wavelength range that is relevant for these quantities depends on the action spectrum applied:
02 October 2012
data product contact: Jos van Geffen & Ronald van der A
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