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Natural Occurrence of Volatile Mono-/Polyhalogenated amd Aromatic/Heteroaromatic Hydrocarbons in Hypersaline Environments
Volatile compounds are important substances for tropospheric and stratospheric chemistry. Anthropogenic sources of specific gases causing greenhouse effect, stratospheric ozone depletion, groundlevel ozone formation and aerosol formation are well known. Additionally, many natural sources, like oceans, wetlands and forests, have been investigated and assessed for their atmospheric impact previously. While emissions from natural sources are often affiliated to biotic mechanisms, model reactions demonstrated also the importance of abiotic reactions. As such furan formation from catechol was successfully accomplished in this work using Fenton chemistry with a well defined biomimetic bispidine Fe2+ complex. Furthermore, abiotic formation of ethylfuran from ethylcatechol was demonstrated. The work in hand also deals with the amalgamation of model reaction and the natural release of volatile compounds from Western Australian salt lakes and the Dead Sea. On the one hand, Fe2+ was determined as the predominant active iron species in most natural hypersaline ecosystems. On the other hand, the release of several aromatic and nonaromatic hydrocarbons, furanoic compounds, sulfur and selenide containing compounds and halogenated compounds was investigated in correlation with geochemical parameters like pH, iron and organic carbon content. Benzene, toluene, ethylbenzene and xylene emissions, normally attributed to anthropogenic sources, correlated significantly with the iron content of Australian salt lake sediments demonstrating their genuine natural abundance. The same was observed for furan and hitherto mostly unnoticed n-alkyl chlorides with a C3-C8 carbon structure. Furthermore, a connection between emissions of methylfurans and their homologoues methylthiophenes was observed indicating a mutual precursor and similar formation mechanism in the soils/sediments. Aside from various known natural chlorinated, brominated and iodinated compounds, new compounds were identified like 3-chlorofuran. Additionally, natural tetrachloromethane formation in acidic salt lakes was postulated supported by various results. Relevance of these compounds for the atmospheric chemistry was assessed with regard to ultrafine particle formation in Western Australia and reactive IO/BrO over the Dead Sea.
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550 Geowissenschaften
550 Earth sciences