Large losses of total ozone in Antarctica reveal seasonal ClO_x/NO_x interaction

Abstract

Recent attempts^1,2 to consolidate assessments of the effect of human activities on stratospheric ozone (O₃) using one-dimensional models for 30° N have suggested that perturbations of total O₃ will remain small for at least the next decade. Results from such models are often accepted by default as global estimates³. The inadequacy of this approach is here made evident by observations that the spring values of total O₃ in Antarctica have now fallen considerably. The circulation in the lower stratosphere is apparently unchanged, and possible chemical causes must be considered. We suggest that the very low temperatures which prevail from midwinter until several weeks after the spring equinox make the Antarctic stratosphere uniquely sensitive to growth of inorganic chlorine, ClX, primarily by the effect of this growth on the NO₂/NO ratio. This, with the height distribution of UV irradiation peculiar to the polar stratosphere, could account for the O₃ losses observed.