The safe refrigerant gas that turned out to be eating the ozone layer
In 1930 Thomas Midgley Jr. inhaled a lungful of his new refrigerant gas before the American Chemical Society and blew out a candle with it, proving it was neither toxic nor flammable. Chlorofluorocarbons replaced deadly fridge gases worldwide, and only decades later did chemists learn what they were doing high in the atmosphere.
Before and during the 1920s, refrigerators ran on ammonia, sulphur dioxide or chloromethane, and leaks of chloromethane killed people. Frigidaire, General Motors and DuPont joined forces to find something harmless, Midgley at GM made the first chlorofluorocarbons, and Frigidaire received the first patent on 31 December 1928. GM and DuPont set up the Kinetic Chemical Company to make Freon, and by 1935 more than 8 million refrigerators using R-12 had been sold.
Their chemistry explains the appeal. Swapping hydrogen in methane or ethane for fluorine and chlorine yields compounds that boil at handy temperatures, dissolve grease well and barely burn, partly because released halogen atoms quench the free radicals that keep flames going. The industry names hide a code: add 90 to a refrigerant number and the three digits give carbons, hydrogens and fluorines, with chlorine filling the rest, so CFC-12 becomes 102, or CCl2F2.
The trouble begins once the molecules drift into the upper atmosphere, where ultraviolet light snaps a carbon-chlorine bond. The freed chlorine atom lingers and keeps converting ozone into ordinary oxygen, thinning the layer that absorbs UV-B radiation; bromine atoms are even more efficient at it. CFCs are potent greenhouse gases too, because they absorb infrared in a band from 7.8 to 15.3 micrometres where the air is otherwise nearly transparent, and their warming grows linearly with quantity rather than tapering off as carbon dioxide's does.
The Montreal Protocol phased out their manufacture in favour of hydrofluorocarbons and related gases. NASA reported in 2018 that the ozone hole had begun to recover, though a 2019 study found rising emissions traced to unregulated use in China.
Source: Chlorofluorocarbon
