Although they are responsible for destroying the barrier that protects life on Earth from harmful solar rays, ozone-depleting gases continue to be used around the world, especially in developing countries. Major advances have been made in controlling the emissions of gases that deplete the ozone layer, which protects life on Earth from the Sun's harmful rays. But the battle will be long one. Chlorofluorocarbons (CFCs) and halons, for example, can remain in the atmosphere for 50 and 65 years, respectively.

1.- What are the principal ozone-depleting gases?

– The best known and most consumed are CFCs, used in refrigerators and air conditioners, as well as in aerosols and some packaging. There are also two gases used as solvents in industry: carbon tetrachloride and methyl chloroform. Add to the list methyl bromide, a widely used fumigant, and the halons used in fire extinguishers.

2.- How do these gases affect the ozone layer?

– Once released, the gases mix with the atmosphere, rising to the stratosphere, where solar rays break their chemical bonds. Chlorine and bromine are released, which contribute to the destruction of ozone molecules. Currently, the depletion of the ozone layer is occurring at a faster pace than its natural regeneration process.

3.- What are the phenomenon's consequences for the environment and human health?

– The destruction of the ozone layer means the loss of the natural barrier against the Sun's harmful ultraviolet rays, particularly UV-B, which can harm the eyes (cataracts) and contribute to skin cancer (melanoma) and suppress the efficiency of the body's immune system. UV-B also produces changes in the chemical makeup of plant species, leading to reduced crop yields, for example, or dying forests. Aquatic life is also affected, particularly zooplankton, the foundation of the ocean food chain.

4.- Can the damage to the ozone layer be reversed?

– If emissions of all ozone-depleting gases were halted today, scientists estimate that natural processes would restore the ozone layer in approximately a half-century, roughly the time that gases like CFCs and halons remain in the atmosphere.

5.- Who are the major consumers of CFCs?

– The United States (2,805 ODP* metric tons) is the leader among industrialized countries. Brazil (6,231 ODP metric tons), China (33,923) and North Korea (6,724) are responsible for 46 percent of the total consumed by developing countries in 2001.

6.- What actions are being taken to control the use of these gases?

– There are 96 chemical substances controlled by the Montreal Protocol, in force since 1987. The aim is to comply with a schedule for eliminating, reducing or substituting these substances. Estimates are that the ozone layer would have lost 50 percent of its volume by 2035 without the Montreal Protocol.

7.- Have the efforts to curb ozone-depleting gas emissions been successful?

– In 1986, the estimated global consumption of CFCs was 1.1 million ODP metric tons, a sum that was reduced to 110,000 in 2001. But new problems have emerged, such as illegal trade in CFCs and the export of refrigeration systems based on CFCs to developing countries, which do not have the same bans as industrialized countries do under the Montreal Protocol.

* Metric tons multiplied by a factor of Ozone-Depleting Potential.

Sources:

http://www.epa.gov/Ozone/ods.html http://toms.gsfc.nasa.gov/ http://www.unep.org/ozone/PressBack/Press-Backgrounder.shtml http://www.undp.org/hdr2003/indicator/indic_316_1_1.html