How did Mario Molina and F. Sherwood Rowland connect CFCs to ozone depletion?

In the early 1970s, chemists Mario Molina and F. Sherwood Rowland theorized that chlorofluorocarbons (CFCs), which were widely used as refrigerants and aerosol propellants, posed a significant threat to the ozone layer.

Their research, published in the journal Nature in 1974, demonstrated that once CFCs are released into the atmosphere, they accumulate in the stratosphere. There, the molecules are exposed to ultraviolet radiation, which causes them to dissociate and release chlorine atoms.123

Molina and Rowland discovered that these chlorine atoms act as catalysts, reacting with and destroying ozone molecules. A single chlorine atom can trigger a chain reaction capable of destroying thousands—or even up to 100,000—ozone molecules before becoming inactive. This critical work established the scientific basis for understanding ozone depletion, eventually leading to international agreements like the Montreal Protocol to phase out these harmful chemicals and protect the Earth from increased ultraviolet radiation.132