OZONE-DEPLETING SUBSTANCES (ODSs)

The thickness of the ozone layer is being reduced by chemicals released due to human activities. Chemicals that deplete the layer are called ozone-depleting substances (ODSs). Many of the ODSs are chlorofluorocarbons (CFCs) - - compounds of chlorine, fluorine and carbon. Other ODSs include halons (which contain bromide and fluorine) used in fire extinguishers.

Chlorine is the main ozone depleting substance in CFCs. When CFCs reach the upper layers of the atmosphere and are exposed to strong ultraviolet light, they breakdown and chlorine atoms are separated from CFC molecules. These chlorine atoms attack the ozone layer.

One chlorine molecule lasts up to 100 years and can destroy as many as 100,000 molecules of ozone. It takes about 10 years for CFCs to reach the ozone layer. This means the CFCs released in 1990 will reach the layer in the year 2000.

Introduction of chlorofluorocarbons (CFCs)

CFCs were first introduced into the atmosphere in the 1930s due to the manufacture of products such as air-conditioners, refrigerators and cold rooms. Since then, CFCs have been used to preserve goods, particularly perishables.

It was 40 years later that scientists realised that CFCs and other gases were damaging the ozone layer. Since then more studies have been carried out to determine the extent of the damage. The studies reveal that some areas are more damaged than others.

Impacts of CFCs on ozone layer

One of the most affected areas is the Antarctica where, during October, an ozone "hole" appears. It is called a hole because some of the layer has been eaten up. In October 1991, scientists found out that about three percent of the protective layer had over the US had been depleted. In October 1993, British scientists discovered the ozone layer over the Antarctic was 67 percent thinner.

By the year 2000, the depletion rate is expected to be double from three to six percent.

EFFECTS OF OZONE-DEPLETING SUBSTANCES

Forests

Ultraviolet light interferes with photosynthesis which enables plants to grow. This leads to reduced crop yields. The ripple effect means less food for animals and ultimately less meat for people. In the oceans, the effect is similar on plant growth, fish and other marine animals.

Ultraviolet light also inhibit plants from adapting to a changing environment. Some studies show that light reduces the ability of plants to fix nitrogen in the atmosphere, an essential element in the growth and productivity.

Agriculture

The effect of the ultraviolet radiation on plants varies from one species to another. Soybeans production falls under increasing dosages of ultraviolet light. The quality of some crops, such as varieties of tomatoes, potatoes and sugar beets also deteriorates when exposed to excess radiation.

Marine areas

In the Southern Sea near the South Pole, the productivity of marine plants is falling and is expected to decline as ozone depletion increases. The impact is worsened by the timing - the ozone is thinnest during the long summer days which bring plenty of sunlight for photosynthesis.

Ozone depletion on people

The depletion of the ozone layer is harmful to people. When people are exposed to the strong ultraviolet light, they can develop skin cancer and eye cataracts. For every one percent decline in the ozone layer, there is potentially a two percent increase in skin cancer.

The ultraviolet light also reduces the ability of the body to fight infections and skin tumours.

There are more cases of skin cancer in countries over which there is greater depletion of the ozone layer. For example, in Australia, which is close to the Antarctica, cancer cases have increased substantially over the past few years.

Effects of CFCs on climate

CFCs contribute to global warming in two ways: First, CFCs are greenhouse gases more potent at trapping heat from the sun than the well known carbon dioxide. Each molecule of CFC 11 and 12 is 10,000 times more effective at trapping heat than a molecule of carbon dioxide. Secondly, by destroying the ozone layer, it allows more heat from the sun leading to more heat near the earth's surface.

PROTECTION OF THE OZONE LAYER

While scientists linked CFCs with ozone layer depletion in the 1970s, the major producers of the chemicals disagreed and continued to manufacture and sell them. In fact, worldwide, CFC production rose by about 50 percent between 1975-1988.

But when the US and Scandinavian governments intervened, producers sought and found substitutes. The world's major CFC producers and users (the industrialised countries) introduced controls to end both production and use of CFCs. This culminated in 1987 Vienna Convention for the Protection of the Ozone Layer.

CFC production fell by 46 percent between 1988-1991 due to the Convention.

Phasing out use of ODSs

Under the Protocol, the major users and producers will phase out CFC production by the year 2000 while developing countries will enjoy a 10-year grace period.Countries that ratify the Protocol are obliged to produce a country programme on how they intend to reduce and phase out the production and use of ODSs. The programme should cover; ODS use and trends, an implementation plan and ODS phasing out projects.

Member countries are also required to enact laws that prohibit trade in ODSs.

The Multilateral Fund

The Multilateral Fund was set up by the industrialised countries to assist poor countries which are signatories of the Protocol.

Signatories of the Protocol who use, at most, an average of 0.3 kilogrammes of ODSs per person per year, are eligible for assistance from the Multilateral Fund.

By the end of July 1993, the Fund had US$127 million which could be accessed by 80 countries - an average of just over US$1.5 million per country. However, some countries get less than others. The Fund has target of US$240 million.

The Multilateral Fund can be used to reduce the burden people in developing countries will face from abiding by the Protocol.

Projects eligible for funding include: training refrigeration and air-conditioning technicians in retrofitting (converting facilities such as refrigerators to use ozone-friendly chemicals); training of customs officials on the control of CFC movement; CFC 12 recovery and recycling projects and replacement of halon installations.

The cost

Almost 90 percent of the cost of observing the terms of the Protocol will arise from converting refrigerators so that they can use the new chemicals. In Zimbabwe, the cost of converting one refrigerator is about US$250. A new one sells at about double this price.

Currently, the cost of the ozone-friendly chemicals to replace CFCs is high - up to five times more expensive. However, as technology and expertise improve, the cost is expected to fall.

At the same time, not all substitutes are more expensive. Ammonia and propane are cheap, and plentiful and are being tried as substitutes in ammonia, which was used in refrigerators before CFCs, is not an attractive alternative as it is toxic and readily catches fire.

Some recommendations

One of the signatories to the Montreal Protocol is Zimbabwe. In March 1994, governmental a meeting to suggest how best to phase out ODSs in compliance with the Protocol.

These were some of the recommendations: For halons the recommendation was to continue to use the remaining 15 tonnes in aircraft, taking it away from other users and stopping the importation of any. The building and surface transport industries should switch on to the substitutes which are too heavy for aeroplanes.

It was also recommended that CFCs should be phased out before the expiry of the grace period. But it was acknowledged that the changeover costs were going to be too high for many consumers and business people and government support was called for.It was further suggested that the necessary legislation should be enacted timeously either under Control of Hazardous Substances Act or under a new statutory regime.