The O3N2O relation from balloon‐borne observations as a measure of Arctic ozone loss in 1991/92

We analyse balloon‐borne measurements of ozone (O3) and nitrous oxide (N2O) in the Arctic, obtained during the European Arctic Stratospheric Ozone Experiment campaign in winter and early spring 1991/92. Using N2O as a long‐lived tracer, we identify chemical ozone depletion in the Arctic vortex in the presence of ozone variations caused by dynamical effects. Substantial chemical ozone loss of about 25% locally over the height range of 15‐21 km, corresponding to the potential‐temperature range of 400‐550 K, is deduced for late winter. Mixing processes can be ruled out as the major cause of the observed anomaly in the O3‐N2O relation by considering the concurrently measured chloroflurocarbon‐11‐N2O relation. The chemical ozone loss derived from the balloon‐borne measurements is in agreement with the loss derived, following the same methodology, from satellite (Halogen Occultation Experiment) vortex observations. Consistent with the dynamical development of the polar vortex and with the observed chlorine activation, the major fraction of the ozone decline occurred before February 1992. The reduced ozone levels persisted over the lifetime of the polar vortex until late March 1992.