Publikationer

DESCARTES is a lightweight instrument for in-situ measurements of long-lived stratospheric tracers from balloons. The instrument is designed to fly piggyback on other payloads; it weighs 16kg and there is no need for telemetry. The instrument collects samples by letting a measured amount of air pass though a tube containing a carboxen adsorbent. The instrument can measure CFC-11 and CFC-113 quantitatively, CCl₄ and CH₃CCl₃ is adsorbed and might give quantitative results after further laboratory analysis. Preliminary results from the four flights with DESCARTES during the THESEO-O₃-loss campaign in the spring of 1999 are presented.

DESCARTES is a lightweight instrument for in-situ measurements of long-lived stratospheric tracers from balloons. The instrument is designed to fly piggyback on other payloads; it weighs 16kg and there is no need for telemetry. The instrument collects samples by letting a measured amount of air pass though a tube containing a carboxen adsorbent. The instrument can measure CFC-11, CFC-113, CCl₄ and CH₃CCl₃ quantitatively. Results from the four flights with DESCARTES during the THESEO-O₃-loss campaign in the spring of 1999 are presented.

DESCARTES is a lightweight balloon-borne grab-sampler instrument for the long-lived chemical tracer CFC-11 developed at the University of Cambridge. From Dec 3, 1999 and throughout 2000 it made 15 flights from Esrange and Andø ya. Simultaneous balloon-borne ozone measurements were made during most flights. The evolution of the polar airmass over the whole year is studied from these flights and compared to model profiles at Kiruna and other subsidence studies.

DESCARTES is a balloon-borne grab-sampler instrument sampling stratospheric trace gases. Sampling and pre-concentration is done by adsorption traps and analysis by gas chromatography. In order to get good focusing for the chromatography the traps should be as small as possible and the lower limit is set by the breakthrough of the adsorbate during sampling. This study focuses on the adsorption behaviour of these traps under different circumstances. The results show that simple theory does not explain adsorption at high flow speed.

DESCARTES is a lightweight balloon-borne instrument for the measurement of long-lived trace gases in the stratosphere. The principle behind the instrument is to let a measured amount of air pass through sample tubes containing the adsorbent Carboxen. The trace gases will then be trapped inside the tubes. DESCARTES is, during a flight, capable of taking 15 samples over a range of altitudes. The samples are analysed after recovery of the instrument using a GC-ECD system. With the current setup DESCARTES is optimised for CFC-11. The objective with this study was to investigate if quantitative adsorption of CFC-11 can be secured during sampling with DESCARTES in the stratosphere. In order to study the adsorption efficiency of the sample tubes, double trap experiments were performed to test for leakage of CFC-11 during sampling. The results indicate that CFC-11 exhibits an exponentially declining distribution inside the adsorbent tube, giving rise to an exponential increase in breakthrough when sampling continuously. The exponential distribution of CFC in the adsorbent tubes of DESCARTES differs from the common way of seeing the sample tube as a chromatographic column. Furthermore the breakthrough of CFC-11 seems to increase exponentially when the flow rate is increased. During a normal flight with DESCARTES, samples are taken at pressure levels from 250 up to 20 hPa. Typical sample sizes are between 30 and 200 scc with flow rates varying from 5 to 200 sccm. If a breakthrough of 5 per cent is acceptable most samples taken with DESCARTES can be seen as safe samples when considering the mass flow. The reduced pressure in the stratosphere will however give rise to enlarged sample volumes, resulting in volume flows of 200 to 600 ml/min. Since the important flow parameter when considering breakthrough seems to be somewhere in-between mass flow and volume flow, breakthrough of CFC-11 exceeding 5 per cent may still be expected due to the high volume flow rates occurring at low pressure.