Environmental Context. Halocarbons can have significant effects on the atmosphere and the environment, particularly with regard to ozone depletion and climate change impacts. The determination of isotopic concentrations for selected halocarbon species should provide useful information to identify and constrain halocarbon sources and sinks within the urban environment. In the present study, a new instrumental method is described to determine these isotope ratios for selected halocarbons and the resultant data are interpreted in terms of local sources and sinks.

Abstract. δ¹³C values of a suite of halocarbons have been determined in an urban background site in Bristol, UK. A novel mobile preconcentration system, based on the use of multi-adsorbent sample tubes, has been developed for trapping relatively large-volume air samples in potentially remote areas. An Adsorption Desorption System–Gas Chromatography–Electron Capture Detector was used to measure the mixing ratios of the selected halocarbon species, while a Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometer was used to determine δ¹³C values. For the species with strong local sources, the variation of isotope ratios has been observed over the experimental period. Some of the results reported in the present study differ from previously reported values and reasons for this are discussed. The reporting of different δ¹³C values for selected halocarbons from different areas in the present study suggests that δ¹³C values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.