Adelaide Brooke cited the ozone as part of the "forty long years" of chaos on Earth from 2019 to 2059. (TV: The Waters of Mars) The ozone layer in Earth's atmosphere was damaged in the course of global warming. In part, this was a plot by the Zygons to transform the planet's atmosphere to make it more amenable to Zygon life. The Zygons encouraged the introduction of modified CFCs Earth's atmosphere, by investing in industrial projects, and releasing any toxic products to the humans which would be harmful to the ozone layer. (AUDIO: The Zygon Who Fell to Earth)
By 1903, an apparatus for producing ozone was invented by Nikola Tesla. (TV: Nikola Tesla's Night of Terror)
In December 1992, the women of Cheldon Bonniface blamed the ozone for the unusual weather. (PROSE: Timewyrm: Revelation)
The Ozone Purge occurred around 2106. (PROSE: Lucifer Rising, AUDIO: An Earthly Child)