Short answers, pulled from the story.
Chlorofluorocarbons (CFCs) are halogenated hydrocarbons containing carbon, fluorine, and chlorine, produced as derivatives of methane, ethane, and propane. They were widely used as refrigerants, aerosol propellants, fire suppression agents, and solvents, with peak annual sales exceeding one billion US dollars and more than one million metric tonnes produced each year.
Thomas Midgley Jr. of General Motors is credited with synthesizing the first chlorofluorocarbons. The Frigidaire corporation received the first patent, number 1,886,339, on the 31st of December 1928. Midgley demonstrated the compound's properties before the American Chemical Society in 1930 by inhaling the gas and using it to blow out a candle.
CFCs have atmospheric lifespans exceeding one hundred years, giving them time to drift into the upper stratosphere. There, ultraviolet radiation breaks the carbon-chlorine bond, releasing chlorine atoms that catalyze the conversion of ozone into ordinary oxygen. Ozone absorbs UV-B radiation, so its depletion allows more high-energy radiation to reach Earth's surface.
The Montreal Protocol is a 1987 treaty forged in response to the seasonal ozone hole over Antarctica, calling for drastic reductions in CFC production. On the 2nd of March 1989, twelve European Community nations agreed to ban all CFC production by the end of the century. According to NASA, by 2018 the ozone layer had begun to recover as a result of CFC bans under the protocol.
Adding 90 to a compound's number gives a three-digit result whose digits encode the count of carbon atoms, hydrogen atoms, and fluorine atoms, with remaining carbon bonds filled by chlorine. For example, CFC-12 yields 90 plus 12, equaling 102: one carbon, zero hydrogen, two fluorine atoms, and two chlorine atoms. Brominated variants use four digits, and isomers are indicated by letters after the number.
CFCs dissolve in seawater at the surface and are transported into the ocean interior, where their concentration reflects both their atmospheric history and ocean circulation patterns. Because CFCs are chemically inert, oceanographers use their partial pressure, particularly the ratio of CFC-11 to CFC-12, to estimate how long a water mass has been out of contact with the atmosphere. Sulfur hexafluoride is now used alongside CFCs to resolve water-dating issues caused by declining atmospheric CFC concentrations since the 1980s.