The Causes of Ozone Depletion
Scientific evidence indicates that stratospheric ozone is being destroyed by a group of manufactured chemicals, containing chlorine and/or bromine. These chemicals are
called "ozone-depleting substances" (ODS).
ODS are very stable, nontoxic and environmentally safe in the lower atmosphere, which is why they became so popular in the first place.
However, their very stability allows them to float up, intact, to the stratosphere. Once there, they are broken apart by the intense ultraviolet light, releasing chlorine and bromine. Chlorine and
bromine demolish ozone at an alarming rate, by stripping an atom from the ozone molecule. A single molecule of chlorine can break apart thousands of molecules of ozone.
What's more, ODS have a long lifetime
in our atmosphere up to several centuries. This means most of the ODS we've released over the last 80 years are still making
their way to the stratosphere, where they will add to the ozone destruction.
The main ODS are chlorofluorocarbons (CFCs), hydrochlorofluorcarbons (HCFCs), carbon tetrachloride and methyl chloroform. Halons (brominated fluorocarbons) also
play a large role. Their application is quite limited: they're used in specialized fire extinguishers. But the problem with halons is they can destroy up to 10 times as much ozone as
CFCs can. For this reason, halons are the most serious ozone-depleting group of chemicals emitted in British Columbia.
Hydrofluorocarbons (HFCs) are being developed to replace CFCs and HCFCs, for uses such as vehicle air conditioning. HFCs do not deplete ozone, but they
are strong greenhouse gases. CFCs are even more powerful contributors to global climate change, though, so HFCs are still the better option until even safer substitutes are discovered.
The Main Ozone-Depleting Substances (ODS)
- Chlorofluorocarbons (CFCs)
- The most widely used ODS, accounting for over 80% of total stratospheric ozone depletion.
- Used as coolants in refrigerators, freezers and air conditioners in buildings and cars manufactured before 1995.
- Found in industrial solvents, dry-cleaning agents and hospital sterilants.
- Also used in foam products such as soft-foam padding (e.g. cushions and mattresses) and rigid foam (e.g. home insulation).
- Used in some fire extinguishers, in cases where materials and equipment would be destroyed by water or other fire extinguisher chemicals. In B.C., halons cause greater
damage to the ozone layer than do CFCs from automobile air conditioners.
- Methyl Chloroform
- Used mainly in industry for vapour degreasing, some aerosols, cold cleaning, adhesives and chemical processing.
- Carbon Tetrachloride
- Used in solvents and some fire extinguishers.
- Hydrofluorocarbons (HCFCs)
- HCFCs have become major, “transitional” substitutes for CFCs. They are much less harmful to stratospheric ozone than CFCs are. But HCFCs they still cause some ozone
destruction and are potent greenhouse gases.
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