A discovery by scientists could make it possible in future to identify the source of banned chlorofluorocarbons being released into the atmosphere. Using mass spectrometers, researchers from the University of East Anglia and the University of Frankfurt analysed air samples collected in the stratosphere by balloons belonging to the French space agency, the Centre National d'Études Spatiales. CFCs have been banned in most countries because of their role in depleting the ozone layer. Because of their long lifetimes, post-ban atmospheric concentrations of the substances were expected to fall slowly: however, the observed decline has been even slower than scientists predicted. Likely reasons for this are the continued use of CFCs, as well as emissions from old refrigerators, air-conditioning systems and waste-disposal units.