A lightweight balloon-borne gas chromatograph for in situ measurements of atmospheric halocarbons

A new lightweight gas chromatograph using a Carboxen microtrap to pre-concentrate the sample has been developed for in situ measurements of stratospheric chlorofluorocarbons (CFCs) from balloon platforms. The instrument has been developed for fast analysis of a single tracer CFC-11 $({\mathrm{CCl}}_{\mathrm{3}}\mathrm{F})$ to maximize the vertical resolution of ascent/descent profiles. In principle a wide range of halocarbons can be measured by changing operational parameters. The instrument weights <25 kg and can easily be deployed on either the balloon flight train or on gondolas. It has a time resolution of <2 min which corresponds to a vertical resolution of 500–700 m for a typical balloon ascent and better for a controlled slow descent. The precision of the CFC-11 measurement is estimated to be 1.7% and the accuracy is currently estimated to be 2.9% with much of the uncertainty arising from the links to the absolute calibration scale. An improved calibration procedure is being developed which should reduce this uncertainty. Test flights were completed in 1998 and the instrument recently participated in the Third European Stratospheric Experiment on Ozone when a number of scientific flights were made.