Ozone is produced naturally in the stratosphere. But "good" ozone is referred to as ozone-depleting substances (ODS), including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, and methyl chloroform. These were are sometimes still used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants. Once released into the air these ozone-depleting substances degrade really slowly. They can remain intact for years as they move through the troposphere until they reach the stratosphere.
