When and where was the ozone hole discovered?

The Montreal Protocol,which calls for appropriate action to protect the ozone layer from human activities,was passed in the year:

Ozone layer depletion or a hole in the ozone layer is primarily found over which region?

Depletion of which gas in the atmosphere can lead to an increased incidence of skin cancers?

In which year was the Montreal Protocol,which aims to protect the ozone layer,signed?

Recognizing the deleterious effects of ozone depletion,an international treaty was signed at Montreal in $1987$ to control the emission of ozone-depleting substances,which is known as $.........$.