ozone-depleting substance

Ozone-depleting substances, usually shortened to ODS, are the category the Montreal Protocol was written to control. The UN Environment Programme describes that treaty as regulating the production and consumption of nearly 100 man-made chemicals referred to as ozone depleting substances, which when released into the atmosphere damage the stratospheric ozone layer that shields people and ecosystems from harmful ultraviolet radiation.

CFCs are the family most people have heard of, but they are one group among several. The treaty's annexes also cover halons, carbon tetrachloride, methyl chloroform, HCFCs and methyl bromide, phased out on different timetables. The US Environmental Protection Agency splits them into Class I, such as chlorofluorocarbons, and Class II, such as hydrochlorofluorocarbons, which were adopted in part as replacements for the first group and are themselves being phased out.

The distinction matters when reading recovery figures. Progress is measured against the whole controlled category rather than CFCs alone, so a story about the ozone layer healing is describing the combined effect of retiring many different chemicals over decades. Worth noting too that not everything the Protocol now controls is an ODS: HFCs were added later for their effect on the climate, and UNEP is explicit that they do not deplete the ozone layer.