Action spectrum - A description of the wavelength dependence of
effects introduced by electromagnetic radiation on biological matter. For
example, a sunburn action spectrum describes the degree to
which varying wavelengths of ultraviolet rays inflict sunburn. It is usually
displayed as a function on a graph.
Aerosols - Small
particles suspended in the air. Examples of aerosols are dust, smog, fog, and
Albedo - The
ratio of radiation reflected from the ground to incoming radiation.
Calibration - A
procedure to convert an instrument's raw data (i.e. voltage) into the physical
unit (i.e. irradiance). For example, instruments for measuring sun light are
calibrated with special lamps. As the irradiance that these lamps
produce is known, radiometers are calibrated by comparing the signal
provoked from the sun light with the signal caused by the lamps'radiation.
Chlorofluorocarbons - Also known as CFCs, are composed of chlorine,
fluorine, and carbon. In the 1970s and 1980s they were extremely popular as
refrigerator coolants and circuit board cleaners, but have since been phased
out due to fact that they contribute to the ozone hole.
Dobson Unit - A unit used to measure the thickness of the ozone layer. It can be
visualized as a tube extending up into the stratosphere, capturing ozone (and
other gases) as it goes. If all of the ozone in that tube was compressed into
the bottom at a standard temperature and pressure, it would form a stack x
millimeters high. This number (x) multiplied by 100 is the number of Dobson Units.
Electromagnetic radiation - Any of a number of types of energy (i.e.
radio waves, micro-waves, ultraviolet rays, infrared or heat rays, light,
X-rays, and gamma rays) that travel at the speed of light.
Erythema - The medical term for sunburn.
Extrapolation - Projecting conclusions from a model or experiment
beyond that of the observed time frame or conditions.
Heterogeneous reactions -
reactions between dissimilar substances (i.e. a liquid and a solid,
or a gas and a liquid).
Irradiance - The amount of radiative power impinging a surface,
divided by the area of this surface. Irradiance is often measured in
the units watts per square meter.
Latitude - The
geographical distance from the equator. Regions close to the equator
have low latitude. The Arctic and Antarctic are at high latitudes.
The United States are in between, at "mid-latitudes".
Melanoma - Most serious form of skin cancer. Melanoma is a malignant
tumor that originates in melanocytes, the cells which produce the
pigment melanin that colors our skin, and is heavily concentrated in
Metastasize - Used most commonly in reference to cancer, it describes
the occurrence of the cancer extending beyond its area of origin into other
regions and organs of the body. When this happens, the cancer becomes difficult
to stop and often results in death.
Nanometer - One billionth of a meter. Unit to measure the wavelength
of UV radiation and light.
Non-melanoma skin cancer - Cancer of the skin's basal cells, which are
at the bottom of the epidermis (outer skin layer) and squamous
cells, which comprise most of the upper layers of skin.
Non-reactive or inert - Name given to a substance that does not react easily
with other substances, and so has a long life expectancy (or in other words, it
remains in its original form for a long time).
Ozone - A molecule composed of three atoms of oxygen and mostly found
in the stratosphere. Ozone absorbs the most dangerous ultraviolet rays before
they can hit the earth, thus protecting life on this planet from its adverse
Photon - Discrete packets of energy that make up electromagnetic
Polar Stratospheric Clouds (PSCs) - Clouds that form during the
winter months in Antarctica and sometimes in the Arctic. Extremely cold
temperatures are necessary for PSCs to exist, and it is on the surface of these
clouds that reactions take place that contribute to the seasonal ozone loss.
Polar vortex - A condition that exists during the winter time in the
Antarctic, in which the air moves in a ringing, circular motion, allowing
little air to come in or out. This is one of the factors resulting in the low
stratospheric temperature during the polar night, which are a
prerequisite for the ozone hole. When the vortex dissipates during
ozone-deprived air can spread over other parts of the
globe, leading to excess UV radiation.
Reactive - A name given to substance that, when introduced to other
substances or molecules, react easily with them and cause the break-up of the
Rickets - A childhood disease in which a lack of vitamin D results in
soft and weakened bones.
Smog - A combination of the words "smoke" and "fog"; it has come to
mean a polluting substance that remains suspended in the air. Smog can be made
up of a variety of matter, such as aerosols, ozone, car exhaust, and sulfurous
compounds, and can also aggravate medical conditions such as asthma or other
Spectroradiometer - An instrument used to measure spectral irradiance.
Spectrum - A range of components, arranged in order. For example, the spectrum of
electromagnetic radiation is the array of wavelengths composing it.
Stratosphere - Area
of the earth's atmosphere just above the troposphere and under the mesosphere.
It takes up an altitude from about 15 km to 50 km above the earth's surface (The
boundaries of these regions are approximate - they vary according to season and
latitude.) The majority of the ozone found in our atmosphere is contained in the
stratosphere, and it is also the location of the ozone hole. In the
stratosphere, the temperature gradually increases until the
stratopause, which is the boundary between the stratosphere and
mesosphere, is reached.
Sun Protection Factor (SPF)
- A number quantifying the effectiveness of
sunscreens. For example, if you can normally stay outside for about
15 minutes before you start to burn, then applying a sunscreen with
an SPF of 20 allows you to stay out for 20 times 15 minutes before
burning, or rather, 300 minutes. The SPF is measured in the
laboratory under standardized conditions, so caution has to be
applied when using it to estimate the time one can actually stay in
the sun. As many sunscreens only block UV-B radiation, they are not
as effective as the SPF suggests in protecting the body from harmful
effects caused by UV-A radiation, like photoaging and possibly
Troposphere - Area
of the earth's atmosphere extending from the surface of the earth up to the
borders of the stratosphere, which is about 15 km above the earth. This
is the area in which we live, and all of the weather takes place. The
troposphere becomes increasingly colder the higher up you go, until the
tropopause (the boundary between the troposphere and
the stratosphere) is reached.
Ultraviolet radiation (or UV radiation) - Electromagnetic radiation
with wavelengths between 100 and 400 nanometers. These rays are emitted from the sun
and are not visible. They inflict increasingly more damage upon a recipient as
the wavelength decreases. Based on its effects, UV radiation is subdivided into
three wavelength ranges named UV-A, UV-B and UV-C:
UV-A covers the
wavelength range 320-400 nm. UV-A is not absorbed by the ozone
layer and is the least harmful UV radiation.
the wavelength range 280-320 nm. UV-B is more energetic than
UV-A, and is partially absorbed by the ozone layer. UV-B rays
that are not filtered out cause sunburn and other harmful
effects to humans.
the wavelength range 100-280 nm. UV-C is the most dangerous form
of UV radiation, but is completely absorbed by the ozone layer.
Artificial UV-C (for example emitted by electric discharges) is
a threat for certain occupational group, like welders.
UV Index - UV Index is a way of expressing the amount of sun-burning
UV radiation. It was invented to inform the public about the intensity of UV radiation,
and is now published in newspapers and on TV. The definition of the UV Index is the
same throughout the world, so it's a great way to learn about the UV hazards at your
travel destinations. The Index is a simple number. 1-3 means low exposure; 4-6 means
medium; 7-9 means high; and more than 10 means extreme exposure.
Mostly wavelengths in the UV-B contribute to the UV Index. The
contribution from the UV-A is only about 10%. Therefore, the
UV Index is highly affected by the thickness of the ozone layer, in
contrast to UV-A radiation.
The time you can stay
outside in the sun at a given UV Index depends also on on your skin type. For example,
if you have fair skin (skin type I) and the UV Index is seven, it takes less than 20
minutes until your skin starts to redden. If you have a dark skin color the same UV
level may need more than 40 minutes to cause an effect. Check out the
UV Index at San Diego measured by the NSF network! During summer it is typically
10 - this means extreme.
Visible light - Electromagnetic
radiation with wavelengths between 380 and 780 nanometers. It is the only
type of radiation that the human eye can see.
Wavelength - A
concept used to describe the energy of electromagnetic radiation, in which the rays are
visualized as traveling in a wave-like pattern. The length of these peaks varies
and is the identifying factor in the type of ray (e.g. x-ray, ultraviolet,
visible). A shorter wavelength means more energy.
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