Season
UV radiation levels peak in late spring and in early
summer. In the winter the peak levels decrease
clearly and may be then 50% to 70% lower than
peak levels in the summer. This can vary depending
on the geographical position.
Weather conditions
Clouds can substantially reduce UV radiation, but
do not block them completely. Heat, humidity and
wind can intensify the UV radiation effect.
Altitude
The UV intensity increases by approximately 3% to
4% per 300 m (1000 feet) above sea level.
On a mountain which is 3000 m (10,000 feet) high
the exposure is 50% higher than at sea level. Winter
sport enthusiasts should be aware of the fact that
snow reflects UV rays additionally and therefore
amplifies the exposure.
Ozone layer
Ozone is a molecule and is found especially in the
upper atmosphere. It filters the UV rays out of the
sunlight. In some parts of the world this protecting
ozone layer is extremely reduced so that a lot more
UV radiation hits the earth at these places.
Reflected UV radiation
White sand reflects from 20% up to 50% of the
incident UV radiation and snow even up to 90%.
Winter sport enthusiasts and others spending time
outdoors in snow-covered areas should be especially
aware. However, as assumed very often, water
reflects a lot less UV radiation so that it is possible to
get sunburn a few meters (feet) under water.
54 Appendix
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