Chlorofluorocarbons (CFCs) were for decades commonly used in the cooling systems of refrigerators and in aerosol cans. However, when these usually inert compounds get zapped by radiation in the upper atmosphere, they are energized and produce chlorine radicals that react with ozone. This has led to a significant depletion in the ozone layer, notably at the North and South Poles. The world was on the brink of losing its natural protection from harmful ultraviolet (UV) rays, mostly thanks to a household appliance used worldwide.
Ironically, CFCs started out as savior compounds, replacing nasty substances such as ammonia and sulfur dioxide in refrigeration equipment. Faulty units would cause unpleasant illnesses and even deaths. The American Thomas Midgley (1889-1944) first proposed CFCs as refrigerants in 1928, demonstrating their suitability with theatrical flourish—he proved their lack of reactivity and toxicity by inhaling the gas and then exhaling onto a lit candle. Developed with the help of Charles Kettering (1876-1958), the new compound was dubbed "Freon," a trademark held by the DuPont company.
Midgley's wonder compound powered a revolution in home refrigeration, and before long nearly every home in the Western world was able to store and enjoy chilled and frozen foods in safety. But the death knell rang in 1974, when research highlighted the harmful nature of CFCs. Restrictions were quickly put in place, and the 1987 Montreal Protocol implemented the gradual elimination of CFCs and similar gases. Although the quantities of CFCs in the atmosphere are now measurably lower, it will take many decades for the ozone layer to fully recover.
