Ozone depletion

Greater UV radiation from ozone depletion causes mutations, skin cancer, eye damage and reduced immunity.
Liver cancer is not one of its health risks.

Ozone is called 'good' or 'bad' depending on where it is found.
Good ozone is found in the upper part of the atmosphere called the stratosphere, where it acts as a shield absorbing the harmful ultraviolet radiation from the sun.
Bad ozone is formed in the lower atmosphere (troposphere), where it is a pollutant that harms plants and animals.
The thickness of the ozone layer is measured in Dobson units.
Hence good ozone is found in the stratosphere.

The Montreal Protocol is an international treaty signed at Montreal, Canada, in 1987 (effective from 1989).
Its aim is to control the emission of ozone-depleting substances such as CFCs, in order to protect the ozone layer of the stratosphere.
Control of $CO_2$ and other greenhouse gases is the aim of the Kyoto Protocol.
Biodiversity conservation was the subject of the Earth Summit at Rio de Janeiro (1992).
Hence the Montreal Protocol aims at the reduction of ozone depleting substances.

The Montreal Protocol was signed at Montreal (Canada) in 1987 and became effective in 1989.
It laid down definite control strategies and time-bound road maps, separately for developed and developing countries, for reducing the emission of CFCs and other ozone-depleting chemicals.
The Vienna Convention (1985) only provided a general framework for protecting the ozone layer, without specific control measures.
The Rio de Janeiro conference (1992) dealt with biodiversity and sustainable development, and the Kyoto Protocol (1997) with greenhouse gases.
Hence the specific control strategies were adopted by the Montreal Protocol.

Ozone in the stratosphere absorbs the harmful ultraviolet radiation of the sun.
Chlorofluorocarbons (CFCs) and other ozone depleting substances release chlorine atoms in the stratosphere, which break down ozone and have caused the ozone hole over Antarctica.
Recognising this, an international treaty known as the Montreal Protocol was signed at Montreal (Canada) in 1987 to control the emission of ozone depleting substances.
It became effective in 1989.
Subsequently many more efforts were made, and protocols have laid down definite roadmaps, separately for developed and developing countries, for reducing the emission of CFCs and other ozone depleting chemicals.
So the Montreal Protocol was passed in the year 1987.