Chlorofluoro Carbons and Ozone Layer Depletion

The association of Chlorofluoro Carbons to the Ozone layer depletion is as a result of common characteristics of a family of organic compounds made up of Carbon (C) and two members of the Halogen: Fluorine (F) and Chlorine (Cl). But some of those characteristics that makes them useful commercial chemicals are responsible for the depletion of the Ozone layer. They are insoluble in water, very unreactive and non biodegradable with half life of 75 years. This allow them to persist in the surrounding for a long period of time so that they can effectively be blown into the stratosphere where they initiate the ozone depleting reaction.

What made the chemicals of the CFCs family attractive was never the more popular negative effect, but because of their inertness, non-flammability and unreactive nature. This make them useful chemicals as Blowing agents, Propellants, Refrigerants and Solvents.

Blowing Agents - CFCs are used as physical blowing agents in foam and polymer industry. Here, the CFC is added to the polymer material and heated to evaporate into tiny bubbles that cool to aerated soft foamy material.

Propellants - Dichlorofluoromethane (CCl₂F) and Trichlorofluoromethane (CCl₃F) are odourless, stable and non-toxic chemicals used in vaporizing and expelling materials from pressurized containers in the form of Aerosol spray. Here, they serve as solvents for Paints, Cosmetics, Insecticides, and other materials pressurized in canisters.

Refrigerants - CFC are also important cooling materials in Refrigerators and air conditioning systems. Initially, they were regarded as better replacement for other refrigerants like sulphur (II) Oxide and Ammonia that are evidently toxic chemicals. Dichlorofluoromethane for example is the active material in Freon that absorbs vapour heat from the immediate environment thus causing cooling in the cooling system.

Solvents - CFCs also find great use in cleaning of what should otherwise be referred to as stubborn stains. Trichlorotrifluoroethane (CCl₃CF₃) is used in removing stains such as grease from electronics and metals.

Two important chemical reactions are essential to the Ozone layer depletion:

1. The dissociation of Ozone gas in the presence of UV light to release atomic oxygen.

O₃(g) → O₂(g) + O(g)

2. The dissociation of CFCs to release Chlorine free radical.

CCl₂F₂(g) → CClF₂(g) + Cl•

Although the atomic oxygen destructively attack the ozone molecule to form molecular oxygen,

O(g) + O₃(g) → 2O₂(g)

atomic oxygen also combine with molecular oxygen to restore the ozone molecule.

O(g) + O₂(g) → O₃(g) + O(g)

Hence there is a fairly constant concentration of Ozone in the atmosphere. But the Problem is how the free chlorine radical destroys the Ozone Layer. The free Chlorine radical Cl• destructively attacks Ozone molecule to form oxochlorate (otherwise called Hypochlorite) (I) ClO and Oxygen molecule.

Cl• + O₃ →ClO + O₂

Oxochlorate (I) formed from the reaction then react with atomic oxygen to produce more chlorine free radicals,

ClO + O → Cl• + O₂

Hence, a cascade of reaction or chain reaction is initiated so that the breakdown of the ozone in the ozone layer is a continuous event.

The World is not closing its eyes on the Ozone depleting effect of CFCs hence the prescription of both political and scientific solutions. This is the reason why several countries signed the Montreal Protocol to stop the use and production of all CFCs materials. The United state and Canada had identified the problem and had in 1978 banned the use of CFCs in Aerosols.

Chemists from around the World are working everyday to create a CFC substitute. This has already given birth to an array of substitutes. An example is the use of Haloalkanes that are not fully halogenated: Hydrochlorofluorocarbons (HCFCs) and Hydrofluorocarbons HFCs). Both compounds are less stable because of the presence of Hydrogen which is hoped could allow the chemical to decompose before it gets to the Stratosphere. 1,1-dichloro-2,2,2-trifluoroethane (CF₃CFCH) is a good candidate because it has a very low percentage of Chlorine, and 1,2,2,2,-tetrafluoroethane (CF₃CH₂F) do not have a single atom of the notorious chlorine. Other ozone safe possible substitutes are: Steam, Propane, Butane, etc.