Abstract. A new set of hygrometers based on the Lyman ct photofragment fluorescence technique has been developed for operation on aircraft and balloons in the stratosphere and upper troposphere. They combine technical details from existing fluorescence hygrometers with several improvements in order to achieve the highest data quality and to minimize maintenance and operational procedures. With these instruments, stratospheric H20 measurements can be accomplished with a precision of < 0.2 ppmv at 1 s integration time, as has been demonstrated both in the laboratory and under field deployment. The design enables a rapid exchange of the air sample of the order of 1 s for fast measurements of small-scale variations of the H20 mixing ratio in the atmosphere. The hygrometer is calibrated using a laboratory calibration bench with approximately 4% accuracy. Measurements made by the hygrometer are compared with a frost point hygrometer during an aircraft mission at H20 mixing ratios from 280 to 8 ppmv, yielding an agreement between both techniques within the instrumental errors.

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Different whole air samplers were flown on large balloons launched from Kiruna (67.9°N; 21.1°E) in the period from 30 November 1991 until 20 March 1992. Thirteen vertical profiles of the N2O mixing ratio were obtained from the analyses of the stratospheric air samples collected at altitudes between about 10 km and 31 km. The series of profile observations illustrates the temporal variation of the vertical structure of the Arctic polar vortex over Northern Scandinavia during EASOE. Already by mid December the N2O mixing ratios observed at the 600 K isentropic level (about 24–25 km) were as low as 20 ppbv, due to the effect of diabatic subsidence. In December subsidence rates of about 100–180 m/day were observed. Dynamic wave activity at the edge of the vortex led to significant sideways erosion at lower altitudes. However, inside the vortex, at altitudes above 600 K, N2O mixing ratios of less than 10 ppbv were observed until the end of March.

Five sets of vertical profiles of long‐lived trace gases were measured in the stratosphere at high northern latitudes (68° N) during three field campaigns of the CHEOPS ‐ Project. Large whole air samples were collected by means of balloon‐borne cryogenic samplers analysed for their content of N2O, CH4, CFCl3, CF2Cl2, C2F3Cl3, CCl4, CH3Cl and CH3CCl3. The measured polar profiles will be compared with mean vertical distributions derived from a series of observations at midlatitudes (44° N). The difference indicates a pronounced effect of subsidence in the Arctic winter stratosphere with a net downward shift of the Arctic vertical profile by about 7 km over the time period from November until February. Owing to this efficient downward transport, the abundance of chlorine in the form of reservoir and reactive species, is increased in the lower Arctic stratosphere to about twice that observed at midlatitudes.

Vertical profiles of stratospheric HO 2 and NO 2 concentrations were determined using matrix isolation and ESR. Up to 10 different samples per flight were collected in situ by a balloon borne cryosampler. Free radicals and trace constituents which are condensable at 68 K are trapped in a polycristalline H~O or D:O matrix. After collection, the samples are stored at a temperature below 83 K until they are analysed in the laboratory by X-band ESR spectroscopy at 4 K. The HO 2 and NO 2 were identified and calibrated by comparison with standard samples collected in the laboratory under typical stratospheric sampling conditions. From several flights over Southern France (44°N) we obtained two profiles of the stratospheric NO 2 mixing ratio. One, from 21 October 1982, agrees well with previous measurements. The other, from 8 October 1981, is lower by one order of magnitude. The few HO 2 data obtained around 35 km altitude agree with previous measurements. An isolated measurement at 17 km altitude is one order of magnitude higher than the model predicted HO 2 concentration.