The Problem
How synthetic chemicals created a hole in the sky.
CFCs and ozone depletion
In the 1920s, chlorofluorocarbons (CFCs) were developed as safe, non-toxic alternatives to dangerous refrigerants like ammonia and sulphur dioxide. They became widely used in refrigeration, air conditioning, aerosol sprays, foam blowing, and industrial solvents. By the 1970s, scientists discovered that these stable molecules drifted to the stratosphere where UV radiation broke them apart, releasing chlorine atoms that catalytically destroyed ozone.
The Antarctic ozone hole
In 1985, British Antarctic Survey scientists reported a dramatic thinning of the ozone layer over Antarctica — the now-famous ozone hole. Each chlorine atom could destroy up to 100,000 ozone molecules before being deactivated. The discovery galvanised global action, leading to the Vienna Convention and Montreal Protocol.
Substance families
Ozone-depleting substances include: CFCs (refrigerants, aerosols, foam), halons (fire extinguishers), carbon tetrachloride (solvents), methyl chloroform (industrial cleaning), HCFCs (transitional refrigerants, still ozone-depleting but less so), and methyl bromide (agricultural fumigant). Each has an ozone depletion potential (ODP) measuring its destructive capacity relative to CFC-11.