CFC products

The decrease of strastospheric ozone was first reported in 1974 and its decrease was linked to the presence of manmade compounds in the atmosphere – the most damaging of which is the class of compounds know as Chloroflurocarbons or CFCs.

CFCs are the major category of man-made halocarbons. Halocarbons are formed when halogen gases such as fluorine, chlorine and bromine become attached to carbon. The smaller halocarbons turn into a gas quite easily and are the prime suspects in ozone depletion.

CFCs are listed as Class I (most harmful) stratospheric-ozone destroyers in Title VI of the United States Clean Air Act Amendments of 1990. Along with halons, carbon tetrachloride and 1,1,1-trichloroethane (methyl chloroform), these chlorine-based chemicals account for about 80 percent of ozone depletion.

CFCs are used in industry in a variety of ways. They were discovered in the 1930s by American chemist Thomas Midgley, and came to be used in refrigerators, home insulation, plastic foam, and throwaway food containers.

The non-reactivity of CFC's, so desirable to industry, allows them to drift for years in the environment until they eventually reach the stratosphere. High in the stratosphere, intense UV solar radiation splits the chlorine molecules off the CFC's. These then attract one of the three oxygen atoms in the ozone molecule (O3) – destroying the ozone by turning it into oxygen. A single chlorine atom can destroy over 100 000 molecules of ozone in this way.

By convection and diffusion, CFCs move upward through the atmosphere until they hit the ozone layer. When the reactive chlorine atoms of disintegrating CFCs collide with ozone (which is also unstable), a chlorine atom from the CFC steals an oxygen atom from the ozone molecule. Created in its place is a useless compound of one chlorine and one oxygen atom (chlorine monoxide) and a two-atom molecule of oxygen.

The oxygen atom of the chlorine monoxide molecule then starts searching for something to react with and bonds with the nearest oxygen atom, freeing the chlorine atom to find a new mate. By this constant change of dance partners, so to speak, a single chlorine atom can destroy 100,000 ozone molecules. Since this is happening a lot faster than Nature can replenish the ozone layer, sending a continuous stream of CFCs into our stratosphere is not a sustainable activity.

Many products that have removed CFCs have replaced them with hydrochlorofluorocarbons (HCFCs or HFCs), a Class II chemical which causes less damage to the ozone layer, but still poses a threat. HCFCs have one-twentieth of the chlorine and more hydrogen, so they break down more easily in the atmosphere's lower levels. But organizations such as the Environmental Defense Fund and the Institute for Energy and Environmental Research oppose the use of HCFCs, saying that much of their chlorine still reaches the ozone layer.

According to the United Nations Environment Programme, there has been a 40 percent drop in CFC consumption since 1986, a reduction beyond that required by the Clean Air Act and the Montreal Protocol. While this is an immense improvement, we still have a long way to go to get to zero ozone-depleting substances.