Dobson Spectrophotometer

It was measurements made using the Dobson Spectrophotometer at Halley that led to the discovery of the hole in the ozone layer. BAS scientists Joe Farman, Brian Gardiner and Jon Shanklin announced their findings in Nature in 1985, sparking rapid international action (as well as a Blue Peter Badge for Jon!)

The ozone hole develops as the Sun returns here at the end of winter. It occurs only over Antarctica and its surrounds. This is because for ozone destruction to take place, not just chlorine from Chloro-Fluoro-Carbons (CFCs) but also extremely cold temperatures and sunlight are essential. In temperatures of -78°C and below, very high ice clouds called polar stratospheric clouds form at the level of the ozone layer. Only on the surface of these clouds, and only with sunlight as a catalyst, can the chemical reactions that begin to destroy ozone take place.

Ozone values started to drop around 1970, soon after CFCs came into use, and continued dropping until around 1999. Since then a very slow recovery has begun. CFCs were banned in the Montreal Protocol from the late 1980s onwards and now, slowly, their levels are dropping at the height of the ozone layer. The ozone hole has started to shrink in response, but it will not disappear completely before the end of the century.