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Observations of the ozone mixing ratio in September in the Antarctic (Left) and March in the Arctic (Right) averaged for a pressure level of 70 (±2) mbar (≈18 km in the heart of the region of ozone depletion). Historical data taken with less accurate methods (Brewer–Mast and Regener; see Materials and Methods and references cited therein) are shown using open symbols. PPMV, parts per million by volume.
