Tropospheric ozone depletion in polar regions A comparison of observations in the Arctic and Antarctic

Abstract

The dynamics of tropospheric ozone variations in the Arctic (Ny-Å lesund, Spitsbergen, 79°N, 12°E) and in Antarctica (Neumayer-Station, 70°S, 8°W) were investigated for the period January 1993 to June 1994. Continuous surface ozone measurements, vertical profiles of tropospheric ozone by ECC-sondes, meteorological parameters, trajectories as well as ice charts were available for analysis. Information about the origins of the advected air masses were derived from 5-days back-trajectory analyses. Seven tropospheric ozone minima were observed at Ny-Å lesund in the period from March to June 1994, during which the surface ozone mixing ratios decreased from typical background concentrations around 40 ppbv to values between 1 ppbv and 17 ppbv (1 ppbv O₃ corresponds to one part of O₃ in 10⁹ parts of ambient air by volume). Four surface ozone minima were detected in August and September 1993 at Neumayer-Station with absolute ozone mixing ratios between 8 ppbv and 14 ppbv throughout the minima. At both measuring stations, the ozone minima were detected during polar spring. They covered periods between 1 and 4 days (Arctic) and 1 and 2 days (Antarctica), respectively. Furthermore, it was found that in both polar regions, the ozone depletion events were confined to the planetary boundary layer with a capping temperature inversion at the upper limit of the ozone poor air mass. Inside this ozone-poor layer, a stable stratification was obvious. Back-trajectory analyses revealed that the ozone-depleted air masses were transported across the marine, ice-covered regions of the central Arctic and the South Atlantic Ocean. These comparable observations in both polar regions suggest a similar ozone destruction mechanism which is responsible for an efficient ozone decay. Nevertheless, distinct differences could be found regarding the vertical structure of the ozone depleted layers. In the Arctic, the ozone-poor layer developed from the surface up to a temperature inversion, whereas in the Antarctic, elevated ozone-depleted air masses due to the influence of catabatic surface winds, were observed.