An assessment of changing ozone loss rates at South Pole: Twenty-five years of ozonesonde measurements

1 In 2010, 25 years of regular, year-round ozone soundings at South Pole station, Antarctica, were completed. These measurements provide unique information about the seasonality, trends, and variability of ozone depletion in the polar stratosphere at high vertical resolution. Here, we focus on the observed loss rates, and their changes since the measurement series began. The fastest loss rates occur between the end of August and end of September between 50 hPa and 30 hPa. Loss rates at these pressure levels increased by approximately 40% from the late 1980s to the late 1990s and have remained stable within estimated uncertainties since then. To estimate the time frame when a reduction in ozone loss rates will be observable outside the range of dynamical variability at the South Pole, we scale the estimated loss rates to the future projected concentrations of equivalent effective stratospheric chlorine (EESC). If a linear relationship between ozone loss rates and EESC is assumed, we project that a change in lower stratospheric ozone loss rates at South Pole station will be first detectable in the 2017–2021 time period.