Identification, fluxes and stable isotope composition of halocarbons released from halogen rich semi-arid environments

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Although it has recently been established that terrestrial ecosystems play an important role in production, consumption and emission of volatile halogenated compounds, they are still very poorly characterized. The objective of these proposed research activities as part of the DFG research unit HALOPROC is to further explore the formation of environmentally-relevant halocarbons such as the halomethanes, chloromethane, bromomethane, iodomethane, chloroform and bromoform; and look for previously uncharacterized emissions of short-lived larger halocarbons from halogen rich soils and associated vegetation. A recently developed fast GC-MS system will be employed to assess these emissions in the laboratory using samples collected in semi-arid salt rich environments (including samples from the first and second phase of the project). In addition stable isotope values of abundant volatile halogenated compounds will be measured from these soil and plant samples. The stable carbon and hydrogen isotope composition (δ13C and δ2H values) of halocarbons will be used to investigate their biogeochemical cycles and global source-sink relationships, as well as the underlying mechanisms. Laboratory based investigations of several environmental parameters influencing the emissions of halocarbons will be conducted. Furthermore, a series of laboratory experiments with varying degrees of complexity will be conducted to gain more information about the underlying mechanisms involved in halocarbon formation in saline soils and halophytes. Instrumentation used in these investigation will also be linked into other activities such as the photochemical/aerosol chamber.