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The Antarctic ‘Ozone Hole’ and Its Possible Global Consequences

T Antarctic 'ozone hole', first observed at Halley Bay by the British team as reported by Farman et al. (1985), and then confirmed by the observational series at the South Pole (Komhyr et al, 1986) as well as by satellite measurements (Nimbus 7, Stolarski et al, 1986), at first provoked a considerable scientific controversy—decreased ozone transport due to changes in stratospheric circulation versus direct photochemical causes. The phenomenon in the Antarctic could not be understood from the current photochemical models; therefore, a number of new photochemical schemes were developed during 1986 (Crutzen & Arnold, 1986; McElroy et al., 1986a, 19866; Rowland, 1986; Solomon et al., 1986), which attempted to explain this new feature. There are differences between them in some details, but all those theories agree in the main points: very low NOX content in the Antarctic lower stratosphere at the end of the polar night, and high concentrations of active chlorine or of other chemical species from which active chlorine is easily produced by photodissociation after the return of the Sun. The new theories assume that N2O5, which originates from NO2 by the action of ozone, is converted to HNO3 by heterogeneous reactions at the surface of aerosols, and/or by cycles including hydrated ions produced by cosmic rays (Crutzen & Arnold, 1986). A basic feature of the further chemical development which takes place is the very low temperature that occurs in the Antarctic lower stratosphere in the latter part of the polar night, due to weaker meridional exchange processes than in the Northern Hemisphere. These temperatures of below -80°C lead to the formation of ice-crystals of a mixture of H2O and HNO3, and thus to an increase of the aerosol mass which can again speed up the catalytic processes at their surface, leading to an almost complete removal of gaseous NOX.