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Optical Radiation > UV Radiation > Sun > Sun, UV radiation and ozone
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Sun, UV radiation and ozone
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As sunlight passes through the earth’s atmosphere, its intensity and spectral distribution are subject to changes caused by absorption, reflection and scattering. gamma-radiation, part of the UV and most of the infrared component are shielded by the upper atmosphere. Visible light reaches the earth in an almost unimpeded manner.
Solar UV radiation
Most of the so-called „solar UV radiation“, i.e. ultraviolet radiation from the sun, is absorbed by ozone in the stratosphere and troposphere. This filter function heavily depends on the UV wavelength. UV radiation intensity at ground level decreases markedly with wavelengths below about 330 nanometre (nm). This phenomenon is also referred to as “UV-B border”. At wavelengths below about 290 nm (UV-C) UV radiation is not measurable any more in our latitudes even in summer.
Variations of ozone content
The total ozone content in our latitudes is subject to natural season variations with a maximum in spring and a minimum in autumn. During the last few years, however, extremely low levels have been recorded particularly in late winter/spring, also referred to as “mini holes in the ozone layer”. This is primarily due to the inflow of ozone-depleted air from subtropical latitudes. In addition, the dispersal of the polar vertex in spring might cause a transfer of polar air with low ozone content to moderate latitudes.
Ozone concentration and UV radiation
As a result of decreasing ozone concentrations in the atmosphere there is an increase especially in the intensity of UV-B radiation, i.e. additional very high energy UV radiation is reaching the ground. The biological effectiveness of this radiation component is very high, and even small variations of the ozone content in the stratosphere, therefore, substantially influence the danger potential of sunlight at the earth’s surface.
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