FOR 763:  Natural Halogenation Processes in the Environment - Atmosphere and Soil

• Subject Area: Geosciences ; Chemistry ; Medicine
• Term: from 2008 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 24881704

To understand on a molecular level the covalent attachment of halide to organic molecules, which are model compounds for humic substances under environmental conditions: Mechanistic laboratory studies will be supported by computational work and will produce detailed information on the various possible reaction pathways, intermediates, products and product distributions with respect to the catalyst structure. The applied analytical techniques available will be UV-VIS-, NIR-, FTIR-, Raman-, Mössbauer- and EPR-spectroscopy, ESI-MS, GC-MS and HPLC-MS.
To evaluate the contribution of microbially induced versus abiotic processes for the formation of organohalogens: Biotic systems will be compared to abiotic systems, and the role of humic substances as either electron shuttle or complexing agent, in particular the role of quinones and complexed metal ions in humic substances for the formation of organohalogens, will be identified.
Further on, the flip side of the coin will be elucidated, where the products of oxidative halogenation are the educts for reductive dehalogenation: Thus the observable product distribution is dependent on the simultaneous formation and degradation of organohalogens.
To investigate halogenation processes on HULIS, dust and sea salt aerosols: The reaction mechanisms for gas-aerosol interactions promoting halogenation will be evaluated by measurements of gas-phase halogen species (DOAS) and of reactive organic substances and particles in smog chamber studies. The analysis of these experiments will be assisted by a numerical model that also makes use of the results from the other laboratory studies and the field of measurements.
To study the amount of natural halogenation processes in different soils depending on Fe- and halide-content and additional crucial soil parameters, such as temperature, moisture, pH, Eh and Corg content: These field parameters and the constraints from the laboratories and the smog chamber will be dovetailed closely in order to assure reasonable comparisons and direct information exchange. The field of work will be conducted in arid regions of Southern Russia and will cover seasonal variations.
To investigate the relevance of natural halogen release processes for the chemistry of the troposphere: Based on the results gained from laboratory and field experiments, a numerical model will be used to explore the importance of halogenation and halogen recycling processes on aerosol particles in dust plumes and of processes on soils (including salt lakes and salt pans). In the second phase of this project parameterisations for halogen release will be developed and implemented in a global three-dimensional model to test the global relevance of the aforementioned processes.

• DFG Programme: Research Units
• International Connection: United Kingdom

Projects

• Coordination of the Research Unit (Applicant Schöler, Heinz-Friedrich )
• Direct and indirect formation of organohalogens by microorganisms (Applicant Kappler, Andreas )
• Experimental and Computational Studies on the Mechanism of Transition-Metal-Catalyzed Oxidation and Halogenation Processes (Applicant Comba, Peter )
• Field and laboratory studies of aerosol formation from halogenated precursor gases (Applicant Held, Andreas B. )
• Formation of volatile organohalogens by microbially catalyzed redox reactions of iron minerals and humic substances (Applicant Kappler, Andreas )
• Identification, fluxes and stable isotope composition of halocarbons released from halogen rich semi-arid environments (Applicant Keppler, Frank )
• Identification of environmentally significant halomethanes using stable isotope techniques (Applicant Keppler, Frank )
• Investigation of reactive halogen species in a smog chamber and in the field (Applicant Platt, Ulrich )
• Naturally produced organohalogens; Atmospheric simulation experiments on halogen activation in aerosol smog chamber facilities with sea salt and secondary organic aerosol (HALOSOA) (Applicant Zetzsch, Cornelius )
• Naturally produced volatile and polar organohalogens in soils (Applicant Schöler, Heinz-Friedrich )

• Spokesperson: Professor Dr. Heinz-Friedrich Schöler
• Deputy: Professor Dr. Cornelius Zetzsch