Ozone is an tri-atomic form of oxygen-it has three atoms instead of the normal two. It is formed naturally in the upper levels of the Earth’s atmosphere by high energy ultraviolet radiation from the Sun. The radiation breaks down oxygen molecules, releasing free atoms, some of which bond with other oxygen molecules to form ozone. About 90% of all ozone in the atmosphere are formed in this way, between 15 and 55 kilometers above the Earth’s surface – the part of the atmosphere called the stratosphere. Hence, this is known as the ‘Ozone layer’. Even in the ozone layer, ozone is present in very small quantities; its maximum concentration, at a height of about 20 – 25 kilometers, in only ten part per million.
Ozone is an unstable molecule. High-energy radiation from the Sun not only creates it, but also breaks it down again, recreating molecular oxygen and free oxygen atoms. The concentration of Ozone in the atmosphere depends on a dynamic balance between how fact it is created and how fast it is destroyed.
2. Why is the Ozone layer important for life on Earth?
The Ozone layer is important because it absorbs ultraviolet (UV) radiation from the sun, preventing most of it from reaching the Earth’s surface. Radiation in the UV spectrum have wavelengths just shorter than those of visible light. UV radiation with wavelengths between 280 and 315 nanometers (a nanometer is one millionth of a millimeter) is called UV-B, and is damaging to almost all forms of life. Absorbing most UV-B radiation before it can reach the Earth surface, the ozone layer shield the planet from the radiation’s harmful effect. Stratospheric ozone also affect the temperature distribution of the atmosphere, thus playing a role in regulating the Earth’s climate.
Ozone is also present in the lower levels of the atmosphere (i.e. the troposphere), but at even lower concentrations than in the stratosphere. Close to the Earth’s surface, most of the Sun’s high-energy UV radiation has already been filtered out by the stratospheric ozone layer, so the main natural mechanism for ozone formation does not operate at this low level. However, elevated concentrations of ozone at ground level are found in some regions, mainly at the result of pollution. Burning fossil fuels and biomass releases compounds, such as nitrogen oxides and organic compounds, which react with Sunlight to form Ozone. This ground level Ozone is a component of urban smog and can cause respiratory problems in humans and damage to plants.
There is little connection between ground level Ozone and the stratospheric ozone layer. Whereas stratospheric ozone shield the Earth from the Sun’s harmful ray’s, ground level Ozone is a pollutant. Though the downward movement of Ozone rich air from the stratosphere contribute to ground level Ozone very little is transported upwards, so Ozone formed due to pollution at the Earth’s surface cannot replenish the Ozone layer. In addition, though ground level Ozone absorbs some ultraviolet radiation, the effect is very limited.
When released to the air, some very stable man-made chemicals containing chlorine and bromine gradually infiltrate all part of the atmosphere, including the stratosphere. Though they are stable in the lower atmosphere, the chemicals are broken down in the stratosphere by the high levels of solar UV radiation, freeing extremely reactive chlorine or bromine atoms. These take part in a complex series of reaction leading to Ozone depletion. A simplified version of the main steps in the Ozone depletion process follows:
The newly freed chlorine and bromine atoms start the process afresh by attacking another ozone molecule. In this way, every one of this atom can destroy thousands of Ozone molecule, which is why very low of chlorine and bromine (the concentration of chlorine in the stratosphere in 1985 was 2.5 part per billion) can break down sufficient Ozone to deplete significantly the vast Ozone layer.
A number of man-made chemicals are capable of destroying stratospheric Ozone. They all have two features in common: In the lower atmosphere they are remarkably stable, being largely insoluble in water and resistant to physical and biological breakdown; and they contain chlorine or bromine (element that are extremely reactive when in a free state) and can therefore attack Ozone. For these reasons, Ozone depleting chemicals remain in the air for long periods, and are gradually diffused to all part of the atmosphere, including the stratosphere. Here they are broken down by intense high energy radiation from the Sun, freeing Ozone - destroying chlorine or bromine atoms.
Chlorofluorocarbons (CFCs) are the most important Ozone destroying chemicals. CFCs have been used in many ways since they are first synthesized in 1928. Some examples are: as a refrigerant in refrigerators and Air conditioners as a propellant in aerosol spray cans; as a blowing agent.
Hydrochlorofluorocarbons (HCFCs) are related to CFCs, and were largely developed as substitutes. Their main uses are as refrigerants and blowing agents. HCFCs are less Ozone destructive than CFCs because their extra hydrogen atom makes them more likely to break down in the lower atmosphere, preventing much of their chlorine from reaching the stratosphere. Nevertheless, the Ozone-Depletion Potential (ODP) HCFCs is too high to allow their long-term use. Forty different HCFCs are subject to global controls leading to an eventual phase out of their use.
Two other chlorine-containing chemicals have significant ODPs and are subject to global controls: carbon tetrachloride and methyl chloroform (1,1,1-trichloroethane). Both chemicals have been widely employed as solvents, mainly for cleaning metals during engineering and manufacturing operations.
The main bromine-containing chemicals that destroy Ozone are called halons. These are bromofluorocarbons (BFCs), the principal use of which has been to extinguish fire. Some halons are potent Ozone destroyers-up to ten times more powerful than the most destructive CFCs. Production of three halons ended in developed countries in 1994, and 34 types of halogenated halons (HBFCs) are due to be phased out under the Montreal Protocol.
In recent years, attention has been focused on another bromine-containing chemical with significant potential to destroy ozone-methyl bromide-which is used mainly as an agricultural pesticide. Due to its Ozone-depletion potential, the 7th Meeting of the Parties to the Montreal Protocol agreed to phase out methyl bromide by 2010 for developed countries, and a freeze at 2002 for developing countries.
The first hypotheses that human activities could damage the Ozone layer were published in the early 1970s. For some years afterwards, it remained uncertain whether Ozone depletion would actually happen, and if so, whether human activities could be to blame. Initially, some thought that emissions of nitrogen oxides from high-flying supersonic aircraft were the main threat. Other argued that man-made chemicals could make only a tiny difference compared with natural sources of potentially Ozone-depleting chemicals, such as volcanoes. This conclusion has been further supported by improved scientific understanding of the chemical mechanisms of Ozone depletion.
Volcanic eruptions can has-ten the rate of Ozone depletion, but their effects are relatively short-lived. In 1991, the eruption of Mount Pinatubo in the Philippines injected some 20 million tones of sulphur dioxide into the atmosphere, which contributed to record levels of Ozone depletion in 1992 and 1993. In the atmosphere, the sulphur dioxide was rapidly converted into sulphuric acid aerosol, increasing the rate of Ozone depletion.
However, stratospheric aerosol concentrations fell to less than a fifth of their peak level in less than two years. By comparison, some CFCs can stay in the atmosphere for more than 100 years; the atmospheric lifetime of CFC-115 is 1700 years.
An international panel of around 295 scientists from26 countries stands firm in its consensus that Ozone depletion is caused by chlorine- and bromine-containing man-made chemicals, mainly CFCs and halons.
Extensive measurements of the Ozone layer by ground-based instruments began in 1957. Since the late 1970s, scientists have taken increasing numbers of measurements of the Ozone layer, using ground-based, balloon- borne and satellite-borne instruments. The measurements have confirmed that Ozone levels are falling almost everywhere in the world. Over the period 1979 to 1994, Ozone over the mid latitudes (30degrees -60degrees) of both hemispheres has been depleted at an average rate of 4-5 per cent per decade. Ozone levels fell faster in the 1980s than in the 1970s, suggesting that Ozone depletion has accelerated.
Depletion varies with latitude. It is lowest over the equator and increases toward the poles. Over the tropics (20 degrees North - 20 degrees South), measurements have shown no significant trend in the total amount of Ozone. For the six months after the eruption of Mount Pinatubo, total Ozone fell by 3-4 per cent. Over the Arctic, cumulative ozone depletion of up to 20 per cent is thought to have occurred in some altitudes, while Ozone loss over the Antarctic has been even grater.
Depletion varies with season. In Northern Hemisphere mid-latitudes over the period 1979-1994, Ozone levels fell twice as fast in winter/spring as in summer/autumn. In the Southern, it became public knowledge in 1985-an event that played an important role in speeding up the international agreement, the Montreal Protocol, to protect the Ozone layer. The Ozone hole is created due to a combination of special factors found only over Antarctica. Each winter, a ‘polar vortex’ isolates a large mass of the Antarctic stratosphere. During the winter, no sunlight falls on this air and it becomes extremely cold. The low temperatures encourage the growth of ice clouds, which provide a surface for special chemical reactions. Despite the absence of sunlight, ‘inactive’ chlorine-containing chemicals are converted into ‘active’ forms, capable of attacking Ozone. When the Sun returns in the spring, this process is speeded up, resulting in very fast destruction of Ozone until the polar vortex breaks up, dispersing the air towards the equator.
Recent experiments in the Arctic have shown that some of the mechanisms necessary for extremely rapid Ozone depletion are present here too. Fortunately, the polar vortex in the Arctic normally breaks up early in the spring (before sunlight has time to destroy large amounts of Ozone) before a full-blown Ozone hole can be created.
Stratospheric Ozone depletion and climate change are both effects of human activities on the global atmosphere. They are distinct environmental problems, but are linked in a a number of ways. Some of the main potential interactions are the following:
Ozone-depleting chemicals contribute to global warming
Ozone depletion can affect climate
Global warming could aggravate Ozone depletion
10. How is UV radiation level changing at the Earth’s surface?
Direct measurement of UV-B radiation levels is technically complicated. However, there is overwhelming scientific evidence that Ozone depletion leads to more UV-B reaching the Earth’ surface and that the amount of increase can be predicted from trends in Ozone levels. On this basis, UV-B at mid latitude is calculated to have increased by 8 - 10 percent over the last 15 years (the calculation is for UV-B radiation at a wavelenghth of 310 nanometers at latitudes 45 degrees north and south over the period 1979-1994). Calculated increases in UV-B to date are large at higher latitude and for shorter waving lengths.
The first persistent increase in UV-B over densely populated areas due to Ozone depletion was measured in 1992/933. Several studies found large increase at northern mid and high latitude. Measurements at Toronto, Canada, suggested that UV-B at 300 nanometers was 35 percent higher than four years previously.
Large increase in UV-B have occurred in Antarctica due to the annual Ozone hole. In 1992, when Ozone depletion was especially severe, UV-B (in the range 298-303 nanometers) at the South Pole was four times than in 1991. Surrounding regions have also been affected, because when the polar vortex breaks down in the spring, large quantities of Ozone depleted air drift toward lower latitudes.
At a measurement station in southern Argentina, biologically weighted levels of UV (a measure taking into account the greater damage caused by shorter wavelengths) were 45 percent higher in December 1991 than is usual at this latitude. The increase was equivalent to moving the site 20 percent closer to the equator.
Based on simulation models, peak levels of biologically weight UV-B reaching the Earth due to Ozone depletion are expected to be significantly higher than measured to date. Relative to 1960 estimated maximum increases for erythema induction and DNA damage at mid-latitudes are shown in the table below. As with the estimates of maximum Ozone depletion given above, the figures are subject to uncertainty; and they assume full compliance from all parties in the global effort to phase out Ozone depleting substances.
11. How does UV radiation affect human skin?
One of the most obvious effects of UV-B radiation is sun-burn, known technically as erythema. Dark skinned people are protected from most of his effect by pigment in their skill cells. UV-B can also damage the genetic materials in skin cells, which can cause cancers. For fair-skinned people, life-long exposure to high levels of UV- B increases the risk of non-melanoma skin cancers. Researchers have suggested that these kinds of skin cancer are likely to increase by 2 percent for each 1 percent decrease of stratospheric Ozone. There is also some evidence that increased exposure to UV-B, especially in childhood, can increase the risk of developing more dangerous melanoma skin cancers.
12. How does UV radiation affect the eye?
In humans, exposure to UV-B from unusual direction can cause snow blindness-actinic keratitis- a painful acute inflammation of the cornea. Chronic exposure can also damage the eye. Enhanced levels of UV-B could lead to more people suffering from cataracts-a clouding of the lens that impairs vision. Cataracts are a leading cause of blindness, even though they can be effectively treated through surgery in regions well provided with medical care.
13. How does UV radiation affect the body’s defense against disease?
Exposure to UV-B can suppress immune response in humans and animals. Increased UV-B could therefore reduce human resistance to a number of diseases, including cancers, allergies and some infectious diseases. In areas of the world where infectious are already a major problem, the added stress from increased UV-B could be significant. This is especially true for diseased, such as leishmaniasis, malaria and herpes, against which the body’s major defence is in the skin. Exposure to UV-B can also affect the body’s ability to respond to vaccination against disease.
The effect of UV-B on the immune system are not dependent on skin color. Dark-skinned and fair skinned people are equally at risk.
14. What effect does UV radiation have on plants?
Many species and varieties of plants are sensitive to UV-B, even at present –day levels. Increase exposure could have complex direct and indirect effects, both on crops and natural ecosystem. Experiments have shown that increase exposure to UV-B of crops such as rice and soy beans result in smaller plants and lower yield. Increased UV-B could alter crop plant chemically, potentially reducing nutritional value or increasing toxicity. If further Ozone depletion is not prevented, we will have to search for UV-B tolerant crops varieties or breed new ones.
The implications for natural ecosystem are difficult to predict, but could be significant. UV-B has a number of indirect effect on plants, such as altering plant form, biomass allocation to parts of the plant and production of chemicals that prevent insect attack. Increased UV-B could therefore lead to ecosystem- level effect, such as changes in competitive balance between plants, animals that eat them and plant pathogen and pests.
15. What are the effects on marine and aquatic life?
Experiments have shown that increase UV-B harms phytoplankton, zooplankton, juvenile fish and larval crabs and shrimps. Harming this small organisms could threaten the productivity of fisheries. More than 30 percent of animal protein consumed by humans comes from the sea, and in many developing countries the share is higher. In Antarctic seas, plankton production has already been reduced under the annual Ozone hole.
Marine life also plays an important role in global climate because phyto-plankton absorbs vast quantities of carbon dioxide, the main greenhouse gas. A decrease in phytoplankton production could leave more carbon dioxide in the atmosphere, contributing to global warming.
16. What are the effects on man-made materials?
Ultraviolet radiation is a primary cause of degradation of some materials, particularly plastics and paints. Increased UV-B will speed up rated of degradation, especially in regions that normally experience high temperature and strong sunshine.
17. What has the international community done to combat ozone depletion?
A strong international consensus that the Ozone layer needs to be protected has developed over the past decade. The first step towards turning consensus into global action was taken in March 1985, ahead of firm scientific proof that man-made chemicals were damaging the Ozone layer.
This was the adoption of the Vienna convention for the protection of the Ozone Layer. Parties to the convention agreed to take the appropriate measures to safe guard the ozone layer and anticipated the negotiation of protocols for specific measures.
The need for a protocol arose almost immediately, when the first evidence of the Antarctic ozone layer hole was published in June 1985. Global negotiations for a protocol were put into top gear and resulted in adoption in September 1987 of the Montreal protocol on substances that deplete the Ozone layer. The Montreal protocol came into force in January 1989 and is the legal basis for the world wide effort to safeguard the ozone layer through controls on production, consumption and use of ozone depleting substances.
By December 1995, 150 countries had ratified the Montreal protocol, so becoming parties to it and legally bound by its requirements. About a third are developed and two-thirds are developing countries. The original Montreal protocol defined measures that parties had to take to limit production and consumption of eight zone depleting substances(ODS), known in the language of the Protocols as ‘controlled substances’. At meetings held in London and Copenhagen in 1990 and 1992 , the controls were strengthened and broadened to cover other chemicals . Instead of merely a reduction in production and consumption of 5 CFCs and 3 halons, the Protocols now requires developed counties to phase out 15 CFCs, 3 halons, 34 HBFCs, carbon tetrachloride and methyl chloroform . A longer –term reduction schedule, also leading to complete phase out, has been agreed for 40 HCFCs. The list of controlled substance is now extended to include: methyl bromide as agreed at the 17th meeting of the parties.
Parties to the Montreal Protocol agreed to reduce and then eliminate the use of ODS before substitute and alternate technologies were fully available. This has proved a successful strategy. Industries and manufactures have already developed alternative substance and technology for almost every formal use of ODS . Many countries are well on their way to a complete phase out of ODS.
Recognizing developing countries’ need for economic development and their relatively low historical use of CFCs, the Montreal Protocol grants developing countries a ‘grace period’ of 10 years more than developed countries to implement the reduction and phase out measures required by the protocols. In addition, at their 1990 meeting in London, the parties created a financial mechanism to provide technical and financial assistance to ‘developing countries’ Ozone protection programmes.
To be eligible to receive support under the financial mechanism, parties must be developing countries and must consume more than 0.3 kg per capita per annum of controlled substance. More than 100 because their status is defined in Article 5 of the Montreal Protocol.
18. How are Ozone – depleting substance being phased out?
Many alternatives exist in the former application of ODS, involving both substitute chemicals and alternative technologies. In existing uses of ODS, conservation, recovery, recycling, and leak prevention are important routes to near – term reduction in emissions. In refrigeration and air conditioning, the main alternative to ODS is to use a non – CFC refrigerant, such as a hydrocarbon or ammonia.
HCFCs are being used in some applications, but only as stop gaps, or ‘ transitional substance’ , since the they too are due to be phased eventually, due to their Ozone-depletion potentials. Some hydrofluoro-carbons (HFCs) are also being used. HFCs contain no chlorine and are Ozone benign however, they are potent green house gasses.
For existing refrigeration and cooling equipment, proper maintenance can reduce leakage considerably. This also cuts costs. Some equipment can be retrofitted for alternative chemicals. CFCs from old refrigerators and air conditioners are increasingly being recovered and recycled before the equipment is disposed off.
In the plastic foam manufacturing industry, CFCs have been used as blowing agents for both rigid (insulating) foams and flexible (structural) foams. Several alternative blowing agents are now in widespread use, including HCFCs, hydrocarbons, methylene chloride, carbon dioxide and water. Several ODS have been used as clearing agents, including CFC -113, carbon tetrachloride, methyl chloroform. They are being replaced in a variety of ways.
Alternatives such as alcohol, terpenes or water, have proved effective for many industrial needs. In the electronic industry, new techniques have made it possible to eliminate cleaning in some operations.
CFCs 11 and 12 have been widely used as propellants in aerosol spray cans in many
countries, this use has already virtually ceased.
Alternative propellants, such as hydrocarbons, have replaced virtually all the former uses of CFCs. In addition, mechanical pumps have been developed that do not needs a chemical propellant at all.
Halons for fire fighting are being replaced with other fire-quenching compounds such as water, carbon dioxide or foam. New high-pressure water mists are being developed for oil and gasoline. Inert where the other solutions have serious drawbacks. Halons in existing fire-fighting equipment are increasingly being reclaimed and stores in halon banks to conserve stocks, prevent emissions to the atmosphere and available for ‘essential uses’ as agreed under the Montreal protocol.
There are two main reasons to convert to Ozone-friendly technologies as soon as possible.
The first is environmental benefit: the total chlorine and bromine loading in the atmosphere will determine how severe Ozone depletion will become and how long it will last. The sooner emissions are stopped; the faster the Ozone layer will repair itself. Only if all companies and all countries cooperate in a rapid phase out of ODS can even more severe Ozone depletion be avoided.
The second is economic benefit: under the terms of the Montreal Protocol, most production of CFCs and halons will cease in the near future. Trade restrictions will further limit supplies. What is left on the market will become scarce and expensive. Companies that abandon ODS early could benefit from lower costs. Industries that switch to Ozone-benign technologies could benefit from consumer demand for Ozone-friendly products. Users of ODS-containing equipment, such as air conditioners and refrigeration units, could save costs by preventing leaks; with the advantage that better maintenance also reduces the likelihood of breakdowns.
Historically, developing countries’ use of ODS and manufacture of import of ODS-containing equipment has been very limited. In 1986, the developing countries in Asia, Africa and Latin America accounted for only 21 per cent of global consumption of CFCs and halons. Developing countries are responsible for even smaller proportion of emissions; 90 per cent of CFCs are currently released in latitudes corresponding to North America, Europe and Japan. World ODS consumption is falling-but not everywhere.
However, as developed countries phase out ODS and others become more industrialized, the developing countries’ share of consumption is increasing. Developed countries accounted for 65 per cent in 1986, but only 47 per cent in 1992. Asia’s share of consumption rose over the same period from 19 to 30 per cent. The consumption share of Eastern Europe increased from 14 to 21 per cent. Trends in the geographical distribution of ODS emissions mean that developing countries’ policies on ODS will become increasingly significant for the global environment. Several Article 5 developing countries are rapidly industrializing; at the same time, economic growth in these countries is creating much greater consumer demand for products that use or contain ODS. Two examples are refrigerators and air conditioners. If the new demands are met by Ozone-destructive technologies, emissions of CFCs and halons will rise drastically.
Increases in population and economic growth in countries such as Brazil, China and India could lead to a doubling of CFC-consumption every five years, and it would soon reach the levels attained by the industrialized nations a few years ago. The demand for ODS in developing countries, if unconstrained, has been calculated at 1 million tonnes in 2010.
Parties to the Montreal Protocol have agreed that developing countries need financial and technical assistance to phase out ODS. To meet this need, the Parties have established the Multilateral Fund as part of the financial mechanism, which assists Article 5 countries with their reduction and phase-out efforts. Contributions to the Fund are made mainly by industrialized countries.
The Fund provides Article 5 countries with financial assistance in developing and implementing projects and proprammes aimed at phasing out ODS. Technical expertise and assistance, information on new technologies, and training and demonstrating programmes can also be provided by the fund.
The Multilateral Fund is managed by an Executive Committee, made up of representatives of 14 parties to the Montreal protocol, with equal representation from developed and developing countries. The committee approves projects funding and develops guidelines for the administration of the Fund. Four organizations have been designated implementing Agencies for the Multilateral Fund.
Culled from FAQ UNEP DTIE Ozone Action Programme website, September 8, 2003.