Stable Carbon Isotope Analysis of Anthropogenic Volatile Halogenated C1 and C2 Organic Compounds

Abstract

Environmental Context.Volatile halogenated organic compounds (VHOCs), ubiquitous trace gases of natural or man-made origin, have gained increasing attention due to their adverse health effects on humans and wildlife, and their potential for catalytic ozone destruction. However, it is difficult to confront VHOC emission budgets as the processes responsible for the formation and degradation of these compounds are complex, and their emission and persistence are affected by variations in the environment and climate. In order to understand VHOCs and reduce their environmental impact, it is necessary to study the isotopic composition of VHOCs produced by different sources, in addition to their concentrations and fluxes in the environment. In this paper, the determination of the carbon isotope range of VHOCs produced by human activities adds useful basic information for future studies of their environmental fate. Abstract. This paper presents the C13/C12 determination of 27 industrial volatile halogenated organic compounds (VHOCs) from different suppliers via gas chromatography combustion isotope-ratio mass spectrometry (GC-C-IRMS). A total of 60 samples, containing one or two carbon atoms, plus chlorine, bromine and iodine substituents, were analyzed to provide a basis for their further comparison with naturally produced VHOC δ13C values. The results indicate a wide range in the carbon isotope signature (–62‰ and –5‰). For chloroiodomethane alone, positive carbon isotope values of 33‰ (Fluka) and 59‰ (VWR International) were found. Each C1 and C2 compound has a distinctive carbon isotope composition, depending on the individual manufacturing reactions, the use of different carbon sources, differences in the composition of the same type of raw material and/or conditions during the manufacturing process. The last two factors are probably responsible for the δ13C discrepancies of ~5‰ found between manufacturers of the same compound. Larger deviations are mainly associated with different carbon isotope signatures of the reactant. Therefore, it is suggested that the reporting of a stable carbon isotope ratio for an anthropogenic VHOC include details of the manufacturing process or alternatively the supplier.