One chlorine atom can wreck around 100,000 ozone molecules
A single chlorine atom freed from a CFC molecule in the stratosphere can destroy about 100,000 ozone molecules before it is finally locked away. That multiplier explains how refrigerants and spray propellants tore a hole over Antarctica, and why the 1987 Montreal Protocol that banned them is counted as the most successful environmental treaty so far.
Ozone, a molecule of three oxygen atoms, is constantly made and unmade high in the atmosphere. Ultraviolet light splits ordinary oxygen into single atoms, which join other oxygen molecules to form ozone; ozone then absorbs harmful UVB rays and breaks apart, only to reform. It is the only atmospheric gas that absorbs UVB, the wavelengths linked to sunburn, skin cancer and cataracts.
Chlorofluorocarbons are so unreactive that they drift intact up to the stratosphere, where ultraviolet light breaks them and releases chlorine. The chlorine grabs an oxygen atom from ozone to form chlorine monoxide, then lets it go and is free to attack again, acting as a catalyst for up to two years until it gets tied up in compounds such as hydrogen chloride. Bromine is even more destructive per atom, though far scarcer. Most stratospheric hydroxyl and nitric oxide radicals are natural, but human activity has sharply raised chlorine and bromine levels.
The damage became visible in the late 1970s. Beyond a general thinning, the Antarctic spring brings a much deeper loss, the ozone hole; reductions of up to 70 percent were first reported in 1985 by Farman and colleagues. Even by 2010, September and October ozone there was still 40 to 50 percent below pre-hole values.
Regulation worked. Controls took effect in 1989, levels stabilised by the mid-1990s, and recovery began in the 2000s. In 2019 NASA reported the smallest hole since discovery, and the UN projects full regeneration by 2045 under current rules, though other estimates put a return to pre-1980 levels nearer 2075. Newer refrigerants, such as the R-1234yf now common in cars, also carry far lower global warming potential than older ones.
Source: Ozone depletion
