Chlorofluorocarbons react with ozone molecules resulting in an ozone hole.
Human-made compounds such as chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and halons destroy ozone in the upper atmosphere (stratosphere). Most of the chlorine entering the stratosphere is from human-made sources (84%), such as CFCs and HFCs, with the remaining 16% from natural sources, such as the ocean and volcanoes. The CFCs, however, are so stable and unreactive that they survive to reach the highest levels of the atmosphere and become globally distributed in the stratosphere. Chlorofluorocarbons are the most abundant ozone-depleting substance. Only when the chlorine atom reacts with some other molecule does it not react with ozone.