Investigation of Arctic ozone depletion sampled over midlatitudes during the Egrett campaign of spring / summer 2000

A unique halocarbon dataset has been obtained using the Australian high altitude research aircraft, the Grob G520T Egrett, during May–June 2000 with GC instrument (DIRAC), which has been previously deployed on balloon platforms. The halocarbon data generally shows a good anticorrelation with ozone data obtained simultaneously from commercial sensors. On 5 June 2000, at 380 K, the Egrett entered a high latitude tongue of air over the U.K. CFC-11 and O3 data obtained on the flight show evidence of this feature. The dataset has been used, in conjunction with a 3D chemical transport model, to infer ozone depletion encountered in the midlatitude lower stratosphere during the flight. We calculate that ozone is depleted by 20% relative to its winter value in the higher latitude airmass. A suite of ozone loss tracers in the model have been used to track ozone depletion according to location relative to the vortex and chemical cycle responsible. The model, initialised on 9 December, indicates that 50% of the total chemical ozone destruction encountered in June in the middle latitudes occurred in the 90–70 N equivalent latitude band and that 70% was due to halogen chemistry.