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on this page: ozone intro | uv
radiation | Ozone depleting gases | ecological effects | uv radiation -
definitions | phytoplankton.
A giant sunshade
The ozone layer acts like a giant sunshade,
protecting plants and animals from much of the sun's harmful ultraviolet
radiation.
Ozone (O3) forms a layer in the stratosphere, 15-40 km above earth surface.
If the ozone in the atmosphere from ground level to a height of 60 km could be
assembled at the earth's surface, it would comprise a layer of gas only about
3 mm thick.
Global stratospheric ozone levels
have declined, which means that the ozone layer is changing. Stratospheric
ozone has large natural temporal and spatial variations, up to 30 percent
variation may be regarded as normal. However, we now have evidence of a
significant thinning of the ozone layer during spring and summer. This is
observed in both the northern and the southern hemispheres at middle and high
latitudes. During the last 10-15 years, the ozone layer above the northern
hemisphere has been reduced by 5-6 percent in spring per decade. The latest
tests (January-March 1995) have shown very large reductions, with a maximum of
more than 30 percent reduction compared to normal.
A depletion of the ozone layer will increase the UV-radiation at ground
level. Increasing doses of UV-B may cause skin cancer, eye
cataracts, damage to the immune system in animals as well as human beings, and
have an adverse impact on plant growth.
The maps shows UV intensity at noon calculated from sun
angle and satelitte measurements of the ozone layer. The model assumes clear
sky conditions at sea level and average sun reflection. With increased
altitude and reflection - for instance snow conditions in mountain areas - the
UV dose can be considerably higher.
The UV index used in the maps above has been developed by
Environment Canada. It runs on a scale from 0 to 10, with 10 being a typical
mid-summer, sunny day in the tropics. A relative scale ranging from low to
extreme is also applied: In extreme conditions (UV Index higher than 9) light,
sensitive and untanned skin may burn in less than 15 minutes.
UV radiation will affect human health through for example sunburn, snow
blindness, other eye damage, early ageing of the skin and rising rates of skin
cancer. It may also cause suppression of the immune response system. It will
likewise affect the productivity of aquatic and terrestrial eco-systems.
Single-celled algae, chlorophyll and plant hormones are especially sensitive
to UV radiation.
As the ozone layer is reduced, the Earth's surface is exposed to more of
the shorter UV wavelengths of the sun's radiation that damage
living things. For each 10 percent depletion of the ozone layer, we can expect
20 percent more radiation in these damaging wavelengths.
Raw material import of CFCs (tons of Ozone Depletion
Potential). Source: SFT, Norwegian State Pollution Control Agency.
The
Ozone Depletion Potential; ODP, is described as a potential
relative to that of CFC-11. The various ozone-depleting
substances vary in the degree to which they contribute to the reduction of the
ozone layer. Halons, for example, are more efficient than CFCs
in depleting ozone, and therefore have a higher ODP.
Chlorofluorocarbons (CFCs), halons, methyl chloroform, methyl
bromide, carbontetrachloride and several other chemicals are ozone-depleting
substances.
When CFCs and halons are released into the atmosphere, they
rise slowly, taking up to seven years to reach the stratosphere. But once they
are there, under the influence of the sun's ultraviolet light, chlorine is
released and react with ozone, with a depletion of the ozone layer as a
consequence. This allows harmful solar UV radiation to pass
through to the earth's surface. Because it takes so long for the
CFCs and halons to reach the stratosphere, any reduction in
their use on earth does not have an immediate effect on the concentration in
the stratosphere. Some of the ozone depleting substances are persistent,
remaining active in the atmosphere for up to 50 years.
Raw material import of halons (ODP tons). Source:
SFT
Most of the CFCs imported to Norway are eventually
emitted into the atmosphere. A minor part is degraded and some is recycled.
Imports of CFCs, halon and carbontetrachloride to Norway have
been stopped. CFC is only allowed used in certain refrigerating
systems.
Halons are only allowed in existing fire extinction plants, but refillment
of halons is prohibited.
Impact on the oceans
Increasing amounts of UV radiation
will have an impact on plankton and other tiny organisms at the base of the
marine food web. These organisms provide the original food source for all
other living organisms in the oceans. Plankton- phytoplankton as well as
zooplankton are highly sensitive to UV radiation, as they lack
the protective UV-B-absorbing layers that higher forms of
plants and animals have. (Phyto = plant. Zoo = animal).
More UV-B radiation reduces the amount of food phytoplankton
create through photosynthesis. Zooplankton, feeding off the phytoplankton, are
also affected. UV-B also damages small fish, shrimp and crab
larvae. It has been estimated that on shallow coastal shelves, a 16 percent
reduction of the ozone layer would kill more than 50 percent of e.g. anchovy
larvae, and cause a 5 percent drop in plankton numbers and a 6-9 percent drop
in fish yield.
Global warming
Ozone-layer depletion seems likely to increase the rate
of greenhouse warming, by reducing the effectiveness of the carbon dioxide
sink in the oceans. Phytoplankton in the oceans assimilates large amounts of
atmospheric carbon dioxide. Increased UV radiation will reduce
phytoplankton activity significantly. This means that large amounts of carbon
dioxide will remain in the atmosphere. A 10 percent decrease in carbon dioxide
uptake by the oceans would leave about the same amount of carbon dioxide in
the atmosphere as is produced by fossil fuel burning.
Impact on land plants.
A high increase in UV radiation
may disrupt many ecosystems on land. Rice production may be drastically
reduced by the effects of UV-B on the nitrogen assimilating
activities of micro-organisms. With a diminishing ozone layer, it is likely
that the supply of natural nitrogen to ecosystems, such as tropical rice
paddies, will be significantly reduced.
Most plants (and trees) grow more slowly and become smaller and more stunted
as adult plants when exposed to large amounts of UV-B.
Increased UV-B inhibits pollen germination.
Increased effects of air pollution
UV-B stimulates the
formation of reactive radicals - molecules that react rapidly with other
chemicals, forming new substances. The hydroxyl radicals, for example,
stimulate the creation of tropospheric ozone and other harmful pollutants.
Smog formation creates other oxidized organic chemicals, such as
formaldehydes. These molecules can also produce reactive hydrogen radicals
when they absorb UV-B. In urban areas, a 10 percent reduction
of the ozone layer is likely to result in a 10-25 percent increase in
tropospheric ozone.
More UV-B radiation seems likely to cause global increases in
atmospheric hydrogen peroxide. This is the principal chemical that oxidizes
sulfur dioxide to form sulfuric acid in cloud water, making it an important
part of acid rain formation.
Damage to materials
UV-radiation causes many materials to degrade more
rapidly. Plastic materials used outdoors will have much shorter lifetimes with
small increases of UV radiation. PVC sidings, window and door
frames, pipes, gutters, etc. used in buildings degrade faster.
Source: UNEP/GEMS library series no 7: The Impact of Ozone layer
depletion
Ultraviolet Radiation
Ultraviolet radiation is divided into three
types, according to wavelength.
UV-A radiation, emitted at wavelenghts of
315-400 nm (1 nanometer is a millionth of a millimeter, or 10 - 9m) is
unaffected by ozone reduction, and is not as harmful as
UV-B.
UV-B radiation, emitted at 280-315 nm, is
affected by decreases in atmospheric ozone. It is UV-B that
causes most of the damage to plants and animals.
UV-B damage depends on the amount of atmospheric ozone that can
act as a filter, the angle of the sun in the sky, and cloud cover, which
shields the surface from some of the ultraviolet radiation.
The ozone layer is usually thinnest at the tropics and thickest towards the
poles.
As stratospheric ozone diminishes, proportionately more of the ultraviolet
radiation reaching the Earth's surface will arrive in the shorter
UV-B wavelenghts.
UV-C radiation, which is lethal, is emitted
at wavelengths of 200-280 nm. Fortunately, UV-C is completely
absorbed by atmospheric ozone and oxygen. Even with severe ozone reduction,
UV-C radiation would still be absorbed by the remaining
ozone.
How to calculate UV intensity:
Look at the
UV intensity map, and find the estimated UV
intensity according to the colour code.
Increasing altitude: add 10 % per 1000 metres.
With white snow: add 100 %
With a decrease in the ozone layer in your area of 10 %: add 20 %.
I.e. with a 50 % reduction in the ozone-layer in your region, the UV-intensity
increases by approximately 100 %.
At sea: add between 5 -10 %.
(UV rays are not so much reflected from the water surface, as they mostly
penetrate it, and may go deep into the water.)
This page is collected from various pages on the "State of the Environment Norway" site. This
is well worth checking out if you haven't had enough already!
Phytoplankton are algae, microscopic single-celled plants that float in the
surface waters of the sea, lakes and rivers. In the ocean they constitute the
base of the marine food web. They have been called 'the pasture of the sea'.
Similar to plants on land they use sunlight to convert carbon dioxide and
water into sugars and oxygen in the process of photosynthesis.
Phytoplankton are tiny and cannot usually be seen individually without a
microscope. They range in size from around 1µm (1/1000mm) to about
1/10mm. However, what they lack in size they make up for in number. Their
concentration is typically around a million cells per litre, but this can rise
to tens of millions of cells per litre. Around 200 different species of
phytoplankton are found in Antarctic waters.
Our research program on phytoplankton in the Southern Ocean is directed to
finding out their importance in the diet of small animals including krill,
their role in the global carbon cycle and the impact on them of increased
ultraviolet radiation caused by the Antarctic 'ozone hole'.
back to ozone info. (top
of this page)
To krill info. To "Krill and
the Circle of Life".
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