Which is the source of chlorofluorocarbons ?

Concept: Chlorofluorocarbons are synthetic compounds built on a short carbon skeleton that carries only chlorine and fluorine atoms and no hydrogen. Because they are volatile, chemically inert, non-toxic and non-flammable, they became the standard working fluid of vapour-compression cooling and were also used as aerosol propellants and foam-blowing agents. Nothing burns to produce them: they are manufactured in a chemical plant, charged into equipment, and released to the air only afterwards.

Application: A sector therefore qualifies as a source only when these compounds are deliberately built into its equipment and then escape from it. Vapour-compression cooling plant carries a volatile refrigerant charge sealed inside a closed circuit; that charge reaches the atmosphere through leaking joints, during servicing and recharging, and when scrapped units are vented instead of having the charge recovered. Refrigeration and air-conditioning is the source the question asks for.

Cross-check: the remaining sectors emit combustion products or soil-chemistry products, not a manufactured halocarbon working fluid.

• Thermal power plants burn pulverised coal, so their stack gas is sulphur dioxide, oxides of nitrogen, carbon dioxide and fly ash.

• Automobiles burn petrol or diesel, so their tailpipe gas is carbon monoxide, oxides of nitrogen, unburnt hydrocarbons and fine particulates.

• Fertilizers add nitrogen to soil, so the gases that follow are ammonia volatilising from urea and nitrous oxide from microbial nitrification and denitrification.

This is exactly why the 1987 Montreal Protocol attacked the cooling sector — refrigerant recovery during servicing, leak-tight equipment and substitute working fluids — to cut chlorofluorocarbon emissions and let the stratospheric ozone layer recover.