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 (CCl3F) 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 flig...