Chlorofluorocarbons

Chlorofluorocarbons (CFCs) are a family of compounds containing chlorine, fluorine and carbon. They are in general unreactive, having low flammability, toxicity and solubility in water.

The major sources of CFCs are aerosol propellants, cleaning solvents, refrigerants and plastic blowing agents.

CFCs such as trichloromethane (CCl₃F) and dichlorodifluoromethane (CCl₂F₂) are normally packed with materials like paint, insecticide or cosmetic preparations in pressurised containers. Upon depressurisation by opening the valve, the propellant vaporises and expels the materials inside the can in the form of aerosol spray.

CFCs like trichlorofluoroethane (CCl₂FCClF₂) can dissolve grease and are widely used as solvents in cleaning electric components and metals.

Freon is a series of CFCs. Dichlorodifluoromethane (CCl₂F₂) is the most important one. Freons absorb heat of vaporisation on evaporation resulting in the cooling of the surroundings. they are widely used as refrigerants in refrigerators and air conditioning units.

In making foam plastic, a volatile CFC, trichlorofluoromethane (CCl₃F) is incorperated in the plastic. The heat evolved during the polymerisation reaction vaporises the CFC which then forms tiny bubbles in the plastic.

Due to their inert behaviour, the once emitted CFCs can stay in the atmosphere for a long time (a few tens of years). They will not be broken down by rainwater. The prolonged effect of CFCs is the depletion of ozone layer. Ultraviolet light generates chlorine radicals that destroy ozone molecules and thus the equilibrium of ozone in the atmosphere. The increased intensity of sunlight may induce health complications (skin cancer, eye cataract) and ecological disasters. (Global warming leads to melting of ice caps in the polar regions. The low-lying land becomes flooded.)