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2 The Culprits 1: Ozone Depleting Substances

When they were discovered in the 1920s, CFCs and other ozone depleting substances (ODS) were “wonder” chemicals. They were neither flammable nor toxic, were stable for long periods and ideally suited for countless applications. By 1973, when scientists discovered that ODS could destroy ozone molecules and damage the shield protecting our atmosphere, they had become an integral part of modern life.

We would get up in the morning from a mattress containing CFCs and turn on a CFC-cooled air conditioner. The hot water in the bathroom was supplied by a heater insulated with CFC-containing foam, and the aerosol cans containing deodorant and hair spray used CFC propellants. Feeling hungry we would open the fridge, also insulated with CFCs. Methyl bromide had been used to grow those tempting strawberries, not to mention many other foodstuffs consumed every day. Nor would there be any escape in the car, with CFCs nesting in the safety foam in the dashboard and steering wheel. At work it was much the same, with halons used extensively for fire protection in offices and business premises, as well as in data centres and power stations. Ozone depleting solvents were used in dry cleaning, and to clean metal parts in almost all electronic devices, refrigerating equipment and cars. They also played a part in tasks such as laminating wood for desks, bookshelves and cupboards.

Since the discovery of their destructive nature, other substances have gradually replaced ODS. In some cases it is difficult to find and costly to produce replacements, which may have undesirable side-effects or may not be applicable for every use. Experts and the public need to remain vigilant to ensure replacements do not cause adverse health effects, safety concerns, or other environmental damage (for example global warming). As is often the case, the last mile on the road to complete elimination is the most difficult one.

ODS can escape during use (for example when used in aerosol sprays), or are released at the end of the lifetime of a equipment if proper care is not taken during its disposal. They can be captured, recycled and re-used if proper procedures are followed by servicing technicians and equipment owners. Disposing of ODS is possible, though it is relatively costly and laborious. These chemicals must be destroyed using one of the destruction processes approved by the Parties to the Montreal Protocol.

Most commonly used ozone depleting substances and their replacements
Substance Characteristics Uses Alternatives
Chlorofluorocarbons (CFCs) Long lived, non toxic, non corrosive, and non flammable. They are also versatile. Depending on the type of CFC, they remain in the atmosphere from between 50 to 1700 years. Refrigerants, cleaning solvents, manufacture of aerosol sprays, blowing agents for plastic foam. Hydrofluorcarbons (HFCs) do not deplete stratospheric ozone, but they are greenhouse gases. Hydrochlorofluorocarbons (HCFCs) do also deplete the ozone layer, but to a much lesser extent. They are being phased out as well. Hydrocarbons are ozone-and climate friendly substances, they are however toxic and flammable, which limits their applications.
Halons Atmospheric lifetime of 65 years. Mobile fire extinguishers, Fire suppression systems in places such as computer rooms and airplanes, explosion protection.  
Methyl chloroform (CHCl3) Toxic. Takes about 5.4 years to break down. Industrial solvent for cleaning, inks, correction fluid.  
Methyl bromide (CH3Br) Takes about 0.7 years to break down. Fumigant used to kill soil-borne pests and diseases in crops prior to planting and as disinfectants in commodities such as stored grains or agricultural commodities awaiting export. Soil solarisation: a plastic cover of a certain thickness on the soil has a pasteurizing effect on the soil. Good results of eliminating harmful pests from the soil are also achieved by mixing residues from certain plant species (marigold – tagetes) varieties. The organic material breaking down in the soil is toxic for certain pests. The method of heating the soil for 30 minutes with steam is expensive and energy-intensive and thus not a real alternative. Soil-less cultures are another option as well as the breeding of pest-resistant varieties.
Hydrochlorofluoro-carbons (HCFCs) Transitional CFC replacements HCFCs deplete stratospheric ozone, but to a much lesser extent than CFCs; however, they are greenhouse gases. Refrigerants, solvents, blowing agents for plastic foam manufacture, and fire extinguishers.