Back to Ozone Depletion Main Page


Dramatic decrease of the Larsen B Iceshelf due to such factors as ozone depletion

Historical Background:


It was in 1956 at Halley Bay, Antarctica that the concern of ozone measurements began. However, it wasn’t until the early 1970’s that accurate satellite measurements of ozone could be taken. Dramatic loss of ozone in the lower stratosphere over Antarctica was first noticed at this time by a research group (consisting of Joseph Farman, Brian Gardiner and Jonathan Shanklin) from the British Antarctic Survey (BAS) who was monitoring the atmosphere above Antarctica from a research station. British Antarctic Survey (BAS) is the UK’s national Antarctic operator as it has been UK’s leading research group in the Antarctica for the past 60 years.

nimbus_7.jpgIn 1978, a complete worldwide measurement was performed with the Nimbus-7 satellite (see image on left) which carried both a TOMS (total ozone mapping spectrometer) and an SBUC (solar backscatter UV meter). Although the TOMS broke down in May 7th 1993, it managed to capture several images measuring ozone concentrations and atmosphere gases of planet Earth up to that point. Scientists noticed a dramatic difference between ozone measurements over time that measuring instruments were deemed faulty. In 1984, when the British first reported their findings, October ozone levels were about 35 percent lower than the average for the 1960s. These measurements were so shocking that replacement instruments were built and sent out only to confirm the results of the earlier experiments. Ozone depletion was occurring rapidly and at a large scale—almost all over the Antarctica continent. In fact, ozone levels drop so low in spring in the Southern Hemisphere that scientists have observed what they call a "hole" in the ozone layer.

Chlorofluorocarbons (CFC’s) are a group of gaseous compounds that contain carbon, chlorine, fluorine, and sometimes hydrogen and are used as refrigerants, cleaning solvents, and aerosol propellants and in the manufacture of plastic foams. They are suspected of being a major cause of stratospheric ozone depletion as wcholoroflourons.gifell as of absorbing long-wave electromagnetic radiation. They were first created in 1928 as non-toxic, non-flammable refrigerants, and were first produced commercially in the 1930's by DuPont. The first Chlorofluorocarbon was a single carbon with two chlorines and two fluorines attached to it.

In 1974 M.J.Molina and F.S.Rowland published a laboratory study demonstrating the ability of CFC's to breakdown Ozone with the help of high frequency UV light. As more time was put into these studies, it was observed that the ozone would be depleted by about 7% in 60 years by CFC alone. Due to this devastating statistic, many nations decided to ban the use of CFC regardless of its useful applications. However, large companies opposed this view as CFC was a key element in many products despite its horrid environmental effects. It was not until 1985 in a field study done by the British Antarctic survey where data showed a 10% increase in ozone depletion then expected that a major phasing in CFC use began.

Since the issue of ozone depletion was relatively new, the cause as well as the existence of the Antarctic ozone hole was still indefinite. However, on September 1987, the Montreal Protocol (The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion) was signed on the basis of quite convincing evidence that the stratosphere had in fact been damaged or disturbed.
  1. The levels of atmospheric chlorine were increasing at about 4-5 per cent per year because of the emissions of chlorofluorocarbons;
  2. theoretical models predicted a chlorine-induced ozone loss, primarily in the upper stratosphere between 30km and 45km;
  3. there was limited observational evidence of ozone loss near 40km; and
  4. a significant loss of ozone was occurring every October above Antarctica, even though its cause had not been conclusively established.
For more information on the exciting history of ozone depletion, click HERE for a historical time-line!

Before we explain the scientific aspect of ozone depletion, this slide-show is a collection of the 'basics' of ozone depletion including the ozone hole and CFC.


Scientific Background:


In order to understand the process of ozone depletion, one must consider the makeup of the earth’s atmosphere. The atmosphere of the Earth may be divided into several distinct layers, as the following figure indicates. However, before we get into that, take a look at the basic workings of ozone depletion in the stratosphere by clicking HERE.

earths_atmopshere_layers.jpgThe Troposphere: The troposphere is where all weather takes place. There is a thin buffer zone between the troposphere and the next layer called the Tropopause.

The Stratosphere and Ozone Layer: Above the troposphere is the stratosphere, where air flow is mostly horizontal. The thin ozone layer in the upper stratosphere has a high concentration of ozone, a particularly reactive form of oxygen (O3). This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun. The formation of this layer is a delicate matter, since only when oxygen is produced in the atmosphere can an ozone layer form and prevent an intense fluctuation of ultraviolet radiation from reaching the surface, where it becomes hazardous to life on Earth. The stratosphere is where ozone depletion is occurring, which is why this process is known as stratospheric ozone depletion


The Mesosphere and Ionosphere: Above the stratosphere is the mesosphere and above that is the ionosphere (or thermosphere), where many atoms are ionized (gained or lost electrons so they have a neutral charge). The ionosphere is very thin, but it is where aurora takes place, and is also responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, which ultimately allows for long-distance radio communication. Stratospheric ozone depletion is a concern because the role of the ozone layer in the stratosphere is to keep a majority (95-99%) of the suns harmful ultraviolet radiation from striking the earth.
depletion_of_ozone_over_time.gif
Ozone (O3) is a colorless gas that is formed when an O2 molecule and atomic O molecule collide. Ozone is composed of three Oxygen atoms, and is unstable. Ozone that exists higher up in the atmosphere protects life on Earth and ozone lower in the atmosphere (troposphere) may be quite toxic. As stated above, most of the ozone in the atmosphere is found in a layer between 15 and 35 km above the earth surface in a region of the atmosphere known as the stratosphere.

In recent years, a large "hole" in the ozone layer has developed over the Antarctic each spring, as well as one over the Arctic region at a smaller size. The ozone layer over southern Canada has thinned by an average of about six per cent since the late 1970s, when human activities that released CFC into the atmosphere affected the ozone layer in the atmosphere. The ozone layer is invisible meaning changes are not physically noticeable. It is only through scientific research that allows us to understand what is happening to this fragile layer of gases in the upper atmosphere.

Ozone Depletion is the damage occurring to the ozone creating holes in it which is heating the earth. The problem of ozone depletion is caused by high levels of chlorine and bromine compounds in the stratosphere. The origins of these compounds are chlorofluorocarbons (CFC). Once formed in the stratosphere by the degradation of a CFC molecule, a single chlorine atom is capable of destroying as many as 10,000 ozone molecules before it is removed from the upper atmosphere.

Stratospheric ozone is very important to life on the surface of Earth because this gas absorbs much of the incoming solar ultraviolet radiation, and thereby shields organisms from its deleterious effects. Stratospheric ozone is formed and consumed naturally by photochemuv_rays_1_b.gifical reactions involving ultraviolet radiation.

About 90 per cent of the Earth's protective ozone layer resides in the stratosphere. Molecular oxygen is broken down in the stratosphere by solar radiation to produce atomic oxygen, which then combines with molecular oxygen to produce ozone. Ozone is destroyed naturally through a series of catalytic reactions involving oxygen, nitrogen, hydrogen and to a lesser extent chlorine and bromine species. The abundance of stratospheric ozone is therefore chemically controlled by the stratospheric abundances of compounds containing hydrogen, nitrogen, chlorine and bromine. Increases in the amount of methane and nitrous oxide thus affect the abundance stratospheric ozone. Stratospheric ozone is also affected by the abundance of carbon dioxide (CO2), because the rates of the chemical reactions that control the abundance of ozone are dependent upon temperature, and the abundance of CO2 plays a key role in determining the temperature structure of the stratosphere.

Human activities have resulted in large increases in emissions of some ozone consuming substances or their precursors into the atmosphere. As a result, there are concerns about potential changes in the dynamic equilibrium among the production and breakdown of ozone (ozone concentration). In the upper atmosphere, atomic oxygen dominates where UV levels are high. Moving down through the stratosphere, the air gets denser, UV absorption increases and ozone levels peak at roughly 20km. As we move closer to the ground, UV levels decrease and ozone levels decrease.


The Impact of Ozone Depletion & Ozone


Without the ozone layer, life would not be as it now is because the layer reflects most of the sun's hot rays back into the atmosphere, if the sun's rays were to hit directly on the Earth, then the Earth would be too hot to have anybody live on it. The effects that this has caused to Antarctica are devastating, between 1980 - 1991, the ozone layer lost over 100 dobson units over the Antarctica’s' atmosphere and is still dropping, at this rate there may be nothing left over the Antarctica and therefore this hole would surely increase and increase in size, which means that it will move its way towards the rest of the Earth, which means we will end up like Antarctica, melting. UV radiation seems responsible for skin cancer in humans; it lowers production of phytoplankton, and thus affects other aquatic organisms. It can also influence the growth of terrestrial plants. Unfortunately it is impossible to stop ozone depletion, however, very possible to reduce the rate of this process, and thus, prolong life on Earth.

effects_of_ozone.jpg

The primary concern regarding ozone depletion is that a decrease in the total column content of ozone leads to an increase in the amount of UV-B radiation reaching the Earth's surface, with adverse effects on human health and ecosystems. While the largest ozone depletion is occurring at high latitudes in both hemispheres, it is happening everywhere except the tropics, and enhanced levels of UV-B radiation will have adverse effects on people of all nations, independent of their geographical position or economic status.

The effects of this are devastating and can have a world wide effect, even if it is only happening in one particular region. For instance, in Antarctica, the ozone layer is damaged throughout the whole area which ultimately leaves the icecaps and glaciers exposed to melting. This is extremely dangerous because these extreme melting results in, more water being pumped into the sea, thus, raising the sea levels and dramatically affecting coastal regions. Furthermore, this drastic increase in temperature will result in the overall increase of the Earth's temperature. Eventually, the Earth's temperature will be so high that life on Earth would be impossible. Animals living in the poles (Antarctica for example) are already suffering the damages of ozone depletion and thus, decrease in overall temperature. The harp seal pups leaving in the northern regions of the earth are suffering dramatically from the depleting ice surfaces. Click HERE to see a video

The ozone layer contains almost all the ozone gas that exists. This is "good" ozone because it protects us from the sun's UV rays. At ground level we find "bad" ozone, as a result of emissions from car exhaust, for example. During the summer it causes smog in large cities. Unfortunately, ground level ozone is increasing while stratospheric ozone decreases. Up in the stratosphere it absorbs some of the potentially harmful ultra-violet (UV) radiation from the sun (at wavelengths between 240 and 320 nm) which can cause skin cancer and damage vegetation, among other things. The ozone layer is beneficial to life on earth as it absorbs the harmful ultra violet (UV) radiation from the sun. In contrast, ozone at ground level, although it also absorbs some UV, is harmful to living organisms. Ground level ozone is produced by sunlight acting on motor vehicle exhaust gases and is a key component of urban smog.good_ozone.gif

The thinning off the earth's ozone layer has allowed greater amounts of skin-burning UV radiation from the sun to reach the earth. Increased exposure to UV has been shown to harm human health, damage freshwater and marine ecosystems, reduce crop yields, and affect forests. In marine ecosystems, UV can damage the tiny single-celled plants, known as phytoplankton, which form the base of the food chain. Decreases in the food source at this early stage, may have effects throughout the entire system, and could ultimately affect fish populations.

skin_cancer.jpgThe most basic impact for humans is the increase in skin cancers. Over-exposure to the sun's UV rays can also cause eye damage, including cataracts, and may even weaken the immune system. UVB radiation can damage several parts of the eye, including the lens, the cornea, and the membrane covering the eye (conjunctiva). "Snow blindness" is the result of overexposure to UVB and occurs in areas of the world with high levels of UV exposure. UV not only affects our eyes and eyesight, but our ability to fight disease. The body's immune system is its first line of defense against invading germs. Recent research has shown that the some viruses can be activated by increased exposure to UV.

Increased UV levels will also have an impact on agriculture, including many of the world's major food crops. It has been observed that some crops, such as barley and oats, have shown decreased growth as a result of exposure to increased UV radiation.

Forestry research found that trees which grow at higher elevations (where UV is naturally stronger) are more resistant. Studies such as these may help us to adapt to increasing UV levels. The effects of UV exposure may be increased during the sudden brief increases which occur in the early springtime when ozone levels fall sharply in the annual cycle. Other concerns include the long-term effect of many years of exposure to higher UV levels and the effect of UV in combination with other stresses on the environment, such as climate change, acid rain and toxic chemicals.

Ozone Depletion in Canada



canada.jpg
Canada has been concerned about stratospheric ozone depletion since the issue was first raised by scientists in the 1960s and 1970s. In fact, our first monitoring programs were established way back in the 1950’s. Since then, our involvement in the issue of the ozone layer has increased. The Brewer ozone spectrophotometer (see image below) was developed in Canada and is presently the principal instrument (most accurate and popular) for ground-based ozone measurements. Furthermore, our collection of monitoring stations is among the largest and most proficient in the world. Canada also remains the archival spot for storing ozone measurements from all around the world in the World Ozone and Ultraviolet Radiation Data Centre, we are responsible for archiving ozone measurements from around the world.

brewer_spectrometer.jpgCanada was one of the original parties to the Montreal Protocol and to be among the many countries that have met or exceeded their obligations under the protocol and its amendments. The Montreal Protocol on Substances that Deplete the Ozone Layer is an international agreement aimed at reversing the damage done to the stratospheric ozone layer that protects the earth from harmful solar ultraviolet radiation. Canada continues to be a leader on ozone protection among the more than 175 countries that are signatories of the Montreal Protocol. On January 1, 1996, the developed countries within the Montreal Protocol decided on eliminating the production of the most damaging ozone depleting substance: CFC. However, further initiatives must still be made to make reducing ozone depletion a global effort.

In 1987, the ozone “hole” or, dramatic thinning of the ozone layer in the Antarctic was noticed, Canada became the first country in the world to take interest in this issue. In 1993, Environment Canada scientists completed the first long-term study which showed that the thinning of the stratospheric ozone layer led to an increase in ultraviolet levels at the earth's surface.

Canadian scientists use a variety of techniques to keep tabs on the ozone layer, including high-altitude research balloons, satellite measurements and ground-based instruments. Two Canadian astronauts, Marc Garneau and Steve MacLean, have even used Canadian instruments to take readings of the ozone layer from inside the space shuttle.

However, despite our tremendous efforts at reducing the damaging effects of global warming, the effects remain devastating. Agricultural and forestry studies have been made on the canada_ozone_level.gifsensitivity of Canadian trees and crops to UV levels. One study found a 10% increase in UV would result in losses of $192 million per year to sensitive crops, such as canola, oats, barley and soybeans.

Since 1979, the annual average amount of stratospheric ozone has dropped globally by 3-6% per decade at mid-latitudes, 12% at high northern latitudes such as northern Canada, and 10-18% at far southern latitudes, such as Antarctica. There has been a similar trend in the depletion of Canadian stratospheric ozone levels since 1980. While the extreme meteorological conditions of the Antarctic are unlikely to occur in the Canadian Arctic, the late-winter/spring ozone levels in the Arctic have been unusually low in six of the last nine years. Due to the long atmospheric lifetimes of ozone-depleting chemicals in the upper atmosphere, ozone levels are not expected to show signs of recovery until at least 2030 - a recovery that could be further slowed by climate change.

On an international level, Canada has been doing quite well in terms of lowering CFC produccfc_phasing.giftion. The global CFC production fell by 88% between 1988 and 1999. Ozone-depleting substances in Canada fell from a high of 27.8 kilo-tonnes in 1987 to about 1 kilo-tonne in 2000. It is predicted that all production of CFC related products will cease by 2022, except for small quantities used for servicing equipment and as laboratory standards.

It has already been discussed that excessive exposure of humans to UV-B causes sunburn and DNA damage, which can lead to skin cancer, depression of the immune system, and an increased risk of cataracts. It is believed that a sustained 1% decrease in stratospheric ozone will result in a 2% increase in cases of non-melanoma skin cancer. The incidence of melanoma in Canada has doubled during the last 20 years.

As mentioned earlier, Canada was one of the first participants of the Montreal protocol. During the late 1980s, nations worldwide got together to discuss solutions to the solving the problem of stratospheric ozone depletion by reducing emissions of ozone depleting substances. In 1989, the Montreal Protocol of the Vienna Convention for the Protection of the Ozone Layer was developed, and today 183 countries have joined this agreement. This protocol ensures that all new reactants that cause ozone depletion except HCFC's and methyl bromide are to be phased out by developed countries by 1996. Methyl bromide will be phased out by 2005, and HCFCs by 2030.

Ozone Depletion in the UK


map_of_england.gifThe largest depletion of ozone occurred over the north and south poles, however during 1997-2001, losses of 3 to 6 per cent compared with pre-1980s levels were observed at mid-latitudes around the UK. Furthermore, over the UK losses of about 6 per cent since 1980 have been noticed. Ozone layer damage extends from the Arctic to northern Europe, including the UK. At Camborne in Cornwall and Lerwick in the Shetland Islands, total ozone concentrations have generally fallen since 1979 although there has been an increase in recent years. The average ozone amounts vary from year to year due to fluctuations in meteorology, but the overall trend for the past 20 years shows a leveling off of the initial decline in total ozone over the UK since the early 1980s. The majority of ozone depletion occurs in the spring. These observations are consistent with the long-term trend of falling ozone amounts over Europe (including the UK) and other northern mid-latitudes.

One of the main reasons for the widespread concern about depletion of the ozone layer is the anticipated increase in the amounts of ultraviolet radiation received at the surface of the Earth and the effect of this on human health and on the environment. Although there is no evidence for a long-term trend in UV-B levels over the UK, there is no doubt that depletion of stratospheric ozone should lead to enhanced UV-B radiation. It is calculated that a 5 per cent decrease in ozone would result in an increase of about 8 per cent in UV-B at the Earth's surface. As stated earlier, increased exposure to UV-B radiation will result in harmful effects on biological systems. In humans these effects include sunburn, skin cancers, damage to the eye and effects on the immune system. Declining ozone values mean UV levels have increased over the UK. UV exposure stops our immune systems working properly. We can develop eye cataracts and skin cancers. Deaths in England and Wales from malignant skin melanomas rose from 200 to 300 per year in the early 1950s to 1766 in 2003. So this is a type of an effect that ozone depletion has on the UK and why it is must be repaired as quick as possible.

Total ozone levels over the UK vary with the seasons, with a maximum of nearly 400 Dobson units (DU) in the early spring and a minimum of a little less than 300 DU in the autumn. This trend also continues through the winter whereby ozone trends can vary even by 50 DU in 24 hours. These drastic changes may be due to both natural and man-made activities. For instance, in the lower atmosphere persistent anticyclonic conditions commonly lead to a reduction in ozone concentrations at heights between 8 and 12 km. This can lead to a significant decrease in the total ozone. Furthermore, in the lower stratosphere the passage of a cold trough is often associated with a temporary reduction in total ozone.

Since there are such varying degrees of ozone concentrations within our atmosphere at a given amount of time, accurate measurements must be taken in order to carefully determine the cause of depleting ozone in the stratosphere. The amount of UV radiation reaching the surface not only depends on the total ozone but also on the elevation of the sun and filtering by clouds and aerosols. When taking these factors into consideration, UV radiation, and thus ozone depletion will undergo further variation. For these reasons, the National Radiological Protection Board (NRPB) maintains a network of sensors for monitoring the levels of UV over the UK.



Ozone Science Crossword Puzzle


Now that you have learned the scientific background as well as the history of ozone depletion, test your knowledge with this cross word!

external image scipuzzl.gif





Across
  • 3. Microscopic animals harmed by excess UV
  • 6. Especially harmful band of UV radiation
  • 11. One atom of this can destroy over 100,000 ozone molecules
  • 12. Unnatural thinning of the ozone layer by human activities
  • 13. Skin _: One of the worst health effects of too much sun
  • 14. _ conditioning: one type of equipment that used CFCs
  • 15. Unit for measuring column ozone
  • 17. _osphere: Part of the atmosphere containing the ozone layer
Down
  • 1. The southernmost continent; location of the ozone hole
  • 2. Wind pattern over Antarctica that isolates the ozone hole
  • 4. Ozone _: region containing most atmospheric ozone
  • 5. Montreal _: Treaty protecting the ozone layer
  • 7. Chemical that makes methyl bromide an ozone-depleting substance
  • 8. Molecule that absorbs UVB radiation from the sun, protecting Earth
  • 9. A substitute for CFCs that's much less damaging to the ozone layer
  • 10. Ultra_: Harmful solar radiation
  • 16. Measure of how much a chemical harms the ozone layer

Words
Cancer, Dobson, Violet, Plankton, Bromine, Layer, HCFC, Depletion, Chlorine,
Protocol, Strat, ODP, Ozone, Air ,Vortex, UVB, Antarctica
Answers
  • 3. Plankton
  • 6. UVB
  • 11. Chlorine
  • 12. Depletion
  • 13. Cancer
  • 14. Air
  • 15. Dobson
  • 17. Strat
Down
  • 1. Antarctica
  • 2. Vortex
  • 4. Layer
  • 5. Protocol
  • 7. Bromine
  • 8. Ozone
  • 9. HCFC
  • 10. Violet
  • 16. ODP

Back to Ozone Depletion Main Page
2.Catholic Teaching and Moral Responsibility
3.International Agreements
4.Possible Solutions
5.References



;