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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.

chart: ozone in earth's atmosphere
Source: Nasa; Shuttle Solar Backscatter Ultraviolett Instrument
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.

UV radiation

january map april map july map october map key

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.


Ozone-depleting gases

cfc's graph
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.


halons graph

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.



Ecological effects

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

UV radiation. Definitions

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


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'.

Visit the Phytoplankton Noticeboard

back to ozone info. (top of this page)
To krill info. To "Krill and the Circle of Life".

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