The discovery of the Antarctic ozone hole

To celebrate its 150 anniversary, Nature collected 10 extraordinary papers published on <italic>Nature</italic>in November, 2019. One of the papers is on the discovery of the Antarctic ozone hole, which was published by three British scientists, Joe C. Farman, Brian G. Gardiner, and Jonathan D. Shanklin, in 1985. They first showed observational evidence that Antarctic stratospheric ozone experienced drastic decrease in the early 1980s, by contrasting to the relative steady state in the 1970s. They also suggested that the ozone hole is due to human-made chlorofluorocarbons (CFCs). <italic>Nature</italic> invited Susan Solomon, who made outstanding contributions to our understanding of the ozone hole, to comment on the paper. She pointed out that “The unexpected discovery of a hole in the atmospheric ozone layer over the Antarctic revolutionized science—and helped to establish one of the most successful global environmental policies of the twentieth century.” The observational evidence by Farman et al. greatly confirmed earlier theoretical works by P. Cruzen, M. Molina, and F. Rowland who first emphasized in the 1970s that anthropogenic emissions of nitrogen oxides and CFCs would damage the ozone layer. Their observational confirmation led to the winning of the Nobel Prize in Chemistry by Cruzen, Molina, and Rowland in 1995. The discovery of the ozone hole also led to great international actions in reducing CFCs emissions and protecting the ozone layer, which is crucially important for screening solar ultraviolet radiation for surface life. A series of conventions has been organized by the United Nations, and the most successful one is the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. The Montreal Protocol and the succeeding amendments, adjustments, and decisions were subsequently negotiated to control the consumption and production of anthropogenic emissions of ozone-depleting substances (ODSs) and some hydrofluorocarbons (HFCs). Since then, ODSs emissions have been largely reduced and showed rapid decrease since the early 1990s. The global ozone layer and the ozone hole over Antarctic all have showed gradual increasing since the late 1990s. According to predictions of climate-chemistry models, the global total column ozone will return to its 1980 values by 2045 when ODSs decline to very low levels, and the Antarctic ozone hole will recover by 2060. The gradual recovery of the ozone hole, due to reducing anthropogenic emissions, from severe depletion also due to human emissions, is considered a successful story that human can protect their environment through self-efforts. It provides us with the confidence that we are able to reduce greenhouse gas emissions and to solve the problem of global greenhouse warming. In the present paper, we will first introduce the discovery of the Antarctic ozone hole by Farman et al. Then, we introduce the chemical mechanisms of the Chapman and the catalytic reactions that result in the formation of the ozone layer, and how anthropogenic perturbations caused the Antarctic ozone hole. We shall also introduce the actions that was taken by international communities to protect the ozone layer. In the final section, we point out the important implications of the discovery of the ozone hole.

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