Sydney Chapman mapped the chemical process that creates and destroys ozone in Earth's upper atmosphere in 1930. Oxygen gas molecules absorb high-energy UVC photons from the sun and split into two atomic oxygen radicals which combine with other oxygen molecules to form triatomic ozone gas.
Chlorine atoms released from human-made chemicals act as catalysts that destroy thousands of ozone molecules before being removed from the stratosphere. A single chlorine atom can react with up to one hundred thousand ozone molecules while bromine atoms are even more efficient at destroying ozone though less bromine exists in the atmosphere.
British Antarctic Survey scientists Farman, Gardiner, and Shanklin reported massive seasonal ozone loss over Antarctica in May 1985. Their findings appeared in the journal Nature and showed values so low they were initially rejected as errors by data quality control algorithms until researchers reran the software without error flags.
Increased surface UVB radiation leads to higher rates of skin cancer and cataracts according to epidemiological studies showing basal and squamous cell carcinomas linked to DNA damage mechanisms. Terrestrial plant productivity drops by about six percent in areas where substantial ozone depletion has occurred due to reduced growth and increased oxidative stress.
Twenty nations signed the Vienna Convention for the Protection of the Ozone Layer in 1985 establishing a framework for international regulations. Representatives from forty-three countries signed the Montreal Protocol later that year agreeing to freeze production of chlorofluorocarbons at 1986 levels.
Atmospheric concentrations of significant compounds have been declining since peaking in 1994 with Effective Equivalent Chlorine dropping ten percent by 2008. The Antarctic ozone hole is expected to return to pre-1980 levels by around 2075 based on current regulations while global stratospheric ozone levels are now increasing toward preindustrial levels.