Abiotic methane formation in oxic soils

Methane plays an important role as a radiatively and chemically active gas in our atmosphere. Until recently, sources of atmospheric methane in the biosphere have been attributed to strictly anaerobic microbial processes during degradation of organic matter. However, some potentially abiotic sources from the biosphere have been discovered in the past few years, starting with methane emissions from plants and plant litter up to the recent discovery of methane production in saprotrophic fungi.rnAlso methane fluxes from aerobic soils have been observed for decades but no alternative source to methanogenesis has been identified so far.rnThis work aims to provide evidence for non-microbial methane formation in soils under oxic conditions. It was found that soils release methane upon heating and other environmental factors like ultraviolet irradiation, and drying-rewetting cycles. The chemical formation of methane during degradation of soil organic matter represents an additional source in soil that helps to understand the methane cycle in aerobic soils. Although the emission fluxes are relatively low when compared to those from aerobic soil sources like wetlands, they may still be important in warm and wet regions subjected to ultraviolet radiation. Therefore this methane source might be highly sensitive to global climate change.rn

Aircraft-based in-situ aerosol mass spectrometry: Chemical characterization and source identification of submicron particulate matter in the free and upper troposphere and lower stratosphere

The composition of the atmosphere is frequently perturbed by the emission of gaseous and particulate matter from natural as well as anthropogenic sources. While the impact of trace gases on the radiative forcing of the climate is relatively well understood the role of aerosol is far more uncertain. Therefore, the study of the vertical distribution of particulate matter in the atmosphere and its chemical composition contribute valuable information to bridge this gap of knowledge. The chemical composition of aerosol reveals information on properties such as radiative behavior and hygroscopicity and therefore cloud condensation or ice nucleus potential. rnThis thesis focuses on aerosol pollution plumes observed in 2008 during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) campaign over Greenland in June/July and CONCERT (Contrail and Cirrus Experiment) campaign over Central and Western Europe in October/November. Measurements were performed with an Aerodyne compact time-of-flight aerosol mass spectrometer (AMS) capable of online size-resolved chemical characterization of non-refractory submicron particles. In addition, the origins of pollution plumes were determined by means of modeling tools. The characterized pollution episodes originated from a large variety of sources and were encountered at distinct altitudes. They included pure natural emissions from two volcanic eruptions in 2008. By the time of detection over Western Europe between 10 and 12 km altitude the plume was about 3 months old and composed to 71 % of particulate sulfate and 21 % of carbonaceous compounds. Also, biomass burning (BB) plumes were observed over Greenland between 4 and 7 km altitude (free troposphere) originating from Canada and East Siberia. The long-range transport took roughly one and two weeks, respectively. The aerosol was composed of 78 % organic matter and 22 % particulate sulfate. Some Canadian and all Siberian BB plumes were mixed with anthropogenic emissions from fossil fuel combustion (FF) in North America and East Asia. It was found that the contribution of particulate sulfate increased with growing influences from anthropogenic activity and Asia reaching up to 37 % after more than two weeks of transport time. The most exclusively anthropogenic emission source probed in the upper troposphere was engine exhaust from commercial aircraft liners over Germany. However, in-situ characterization of this aerosol type during aircraft chasing was not possible. All long-range transport aerosol was found to have an O:C ratio close to or greater than 1 implying that low-volatility oxygenated organic aerosol was present in each case despite the variety of origins and the large range in age from 3 to 100 days. This leads to the conclusion that organic particulate matter reaches a final and uniform state of oxygenation after at least 3 days in the free troposphere. rnExcept for aircraft exhaust all emission sources mentioned above are surface-bound and thus rely on different types of vertical transport mechanisms, such as direct high altitude injection in the case of a volcanic eruption, or severe BB, or uplift by convection, to reach higher altitudes where particles can travel long distances before removal mainly caused by cloud scavenging. A lifetime for North American mixed BB and FF aerosol of 7 to 11 days was derived. This in consequence means that emission from surface point sources, e.g. volcanoes, or regions, e.g. East Asia, do not only have a relevant impact on the immediate surroundings but rather on a hemispheric scale including such climate sensitive zones as the tropopause or the Arctic.

Characterization of primary biogenic aerosol particles by DNA analysis: Diversity of airborne Ascomycota and Basidiomycota

Primary biogenic aerosol (PBA) particles account for large proportions of air particulate matter, and they can influence the hydrological cycle and climate as nuclei for water droplets and ice crystals in clouds, fog, and precipitation. Moreover, they can cause or enhance human, animal, and plant diseases. The actual abundance and properties of PBA particles and components in the atmosphere are, however, still poorly understood and quantified. rnIn this study, the identity, diversity, and frequency of occurrence of PBA particles were investigated by DNA analysis. Methods for the extraction, amplification, and analysis of DNA from aerosol filter samples were developed and optimized for different types of organisms, including fungi, bacteria, and plants. The investigations were focused on fungal DNA, and over 2500 sequences were obtained from air samples collected at different locations and climatic zones around the world (tropical, mid-latitude, sub-polar; continental, marine). rnNearly all fungal DNA sequences could be attributed to the phyla of Ascomycota and Basidiomycota. With regard to species richness, the ratio of Basidiomycota to Ascomycota was much higher in continental air samples (~60:40) than in marine air samples (~30:70). Pronounced differences in the relative abundance and seasonal cycles of various groups of fungi were detected in coarse and fine particulate matter from continental air, with more plant pathogens in the coarse and more human pathogens and allergens in the respirable fine particle fraction (<3 ��m). The results of this study provide new information and insights into the sources of PBA particles and the interactions of the biosphere with the atmosphere, climate, and public health. rn

Stable isotope fractionation of selenium by biomethylation in soil

Selen ist in geringen Mengen ein essentielles N��hrelement, das aber in h��heren Gehalten toxisch wird. Der Se-Kreislauf in der Umwelt ist eng mit Redoxreaktionen wie der Reduktion von Se-Oxyanionen zu Methylselenid verkn��pft. Fl��chtige Methylselenide sind weit verbreitet und stellen einen wichtigen Se-Fluss in der Umwelt dar. Das ��bergeordnete Ziel meiner Dissertation war, die Stabilisotopenfraktionierung von Se durch Biomethylierung verschiedener oxidierter Se-Spezies (Se[IV] und Se[VI]) im Boden aufzukl��ren. Zun��chst wurde eine Methode entwickelt, die es erlaubte fl��chte Methylselenide quantitativ zur��ckzuhalten. Es zeigte sich, dass alkalische Peroxid-L��sung daf��r geeignet war. Mit alkalischer Peroxid-L��sung wurde eine Wiederfindung von 95,6 �� Standardabweichung 5,4% in Verfl��chtigungsexperimenten mit Methylselenid-Standards erreicht. Bei Einsatz von alkalischer Peroxid-L��sung in geschlossenen Mikrokosmos-Experimenten kam es zu keinen Se-Verlusten und ausgeglichenen Se-Isotopenbilanzen. Die massengewichteten ��82/76Se-Werte lagen f��r Se(IV) und Se(VI) am Ende der Mikrokosmos-Inkubationen bei -0,31 �� 0,05��� (n = 3) und -0,76 �� 0,07��� (n = 3) verglichen mit -0,20 �� 0,05��� und -0,69 �� 0,07��� im jeweils zugegebenen Se. Im zweiten Teil meiner Dissertation wurde die Pilzart Alternaria alternata mit Se(VI) und Se(IV) in geschlossenen Mikrokosmen f��r 11-15 und Se(IV) zus��tzlich f��r 3-5 Tage bei 30��C inkubiert. In 11-15 Tagen wurden 2,9-11% des Se(VI) und 21-29% des Se(IV) und in 3-5 Tagen, 3-5% des Se(IV) methyliert. Die anf��nglichen ��82/76Se-Werte von Se(VI) und Se(IV) lagen bei -0,69 �� 0,07���, und -0,20 �� 0,05���. Die ��82/76Se-Werte der Methylselenide unterschieden sich nach 11-15 Tagen Inkubation signifikant zwischen Se(VI) (-3,97 bis -3,25 ���) und Se(IV) (-1,44 bis -0,16���) als Quellen. Die ��82/76Se-Werte der Methylselenide zeigen also die Quellen der Biomethylierung von Se an. Die k��rzere Inkubation von Se(IV) f��r 3-5 Tage f��hrte zu einer ausgepr��gten Se-Isotopenfraktonierung von mindestens -6���, bevor ein Flie��gleichgewicht erreicht wurde. Im dritten Teil bestimmte ich die Bindungsformen von Se mit drei operativ definierten sequentiellen Extraktionen und die ��82/76S-Werte des gesamten Selens in zehn urbanen Oberb��den mit 0,09-0,52 mg/kg Se, die f��nf verschiedene Landnutzungstypen repr��sentierten (��berschwemmungsgr��nland, Garten, Park, Stra��enrand und Wald). Nur ein kleiner Teil des Seleniums lag in austauschbarer und damit direkt bioverf��gbarer und in residualer, wenig reaktiver Form vor. Das meiste Se war an die organische Substanz und Fe-(Hydr-)Oxide gebunden (42-77% des gesamten Selens). Der mittlere ��82/76Se-Wert des gesamten Selens in den Oberb��den lag mit -0,03 �� 0,38��� nahe beim Mittelwert der gesamten Erde. Geringf��gig niedrigere Se-Isotopensignale von -0,59 bis -0,35��� v.a. in Waldb��den und geringf��gig h��here von 0,26 to 0,45��� in ��berschwemmungsgr��nland wurden vermutlich durch Boden-Pflanze-Recycling und Se-Kontaminationen durch das Flusswasser verursacht. Der vierte Teil umfasste ein ���Natural Attenuation���-Experiment und Mikrokosmos-Inkubationen von Bodenproben mit A. alternata. Die Equilibrierung von zum Boden gegebenem Se(IV) und Se(VI) f��r drei Tage f��hrte zu abnehmenden wasserl��slichen Se-Gehalten um 32-44% bzw. 8-14, die mit kleinen Isotopenfraktionierung (�� = -0,045 bis -0,12 ��� and -0,05 to -0,07��� verbunden waren. In zwei der inkubierten B��den mit m����ig sauren pH-Werten wurden zwischen 9,1 und 30% des zugef��gten Se(IV) und 1,7% des zugef��gten Se(VI) methyliert w��hrend in einem stark sauren Boden keine Methylierung auftrat. Das aus Se(IV) entstandene Methylselenid war deutlich gegen��ber dem zugegebenen Se-Standard (0,20���) an 82Se verarmt (��82/76Se = -3,3 bis -4,5���). Meine Ergebnisse zeigen, dass die stabilen Isotopenverh��ltnisse von Se neue Einblicke in Se-Transformationsprozesse erlauben.rn

Stationary in-situ measurements of aerosols, gaseous pollutants and meteorology : chemical and physical characterization of natural and anthropogenic sources

Natural and anthropogenic emissions of gaseous and particulate matter affect the chemical composition of the atmosphere, impact visibility, air quality, clouds and climate. Concerning climate, a comprehensive characterization of the emergence, composition and transformation of aerosol particles is relevant as their influence on the radiation budget is still rarely understood. Regarding air quality and therefore human health, the formation of atmospheric aerosol particles is of particular importance as freshly formed, small particles penetrate into the human alveolar region and can deposit. Additionally, due to the long residence times of aerosol particles in the atmosphere it is crucial to examine their chemical and physical characteristics.This cumulative dissertation deals with stationary measurements of particles, trace gases and meteorological parameters during the DOMINO (Diel Oxidant Mechanism In relation to Nitrogen Oxide) campaign at the southwest coast of Spain in November/December 2008 and the ship emission campaign on the banks of the Elbe in Freiburg/Elbe in April 2011. Measurements were performed using the Mobile research Laboratory ���MoLa��� which is equipped with state-of-the-art aerosol particle and trace gas instruments as well as a meteorological station.

Development, characterization, and application of flowing atmospheric-pressure afterglow ionization for mass spectrometric analysis of ambient organic aerosols

Addressing current limitations of state-of-the-art instrumentation in aerosol research, the aim of this work was to explore and assess the applicability of a novel soft ionization technique, namely flowing atmospheric-pressure afterglow (FAPA), for the mass spectrometric analysis of airborne particulate organic matter. Among other soft ionization methods, the FAPA ionization technique was developed in the last decade during the advent of ambient desorption/ionization mass spectrometry (ADI–MS). Based on a helium glow discharge plasma at atmospheric-pressure, excited helium species and primary reagent ions are generated which exit the discharge region through a capillary electrode, forming the so-called afterglow region where desorption and ionization of the analytes occurs. Commonly, fragmentation of the analytes during ionization is reported to occur only to a minimum extent, predominantly resulting in the formation of quasimolecular ions, i.e. [M+H]+ and [M–H]– in the positive and the negative ion mode, respectively. Thus, identification and detection of signals and their corresponding compounds is facilitated in the acquired mass spectra. The focus of the first part of this study lies on the application, characterization and assessment of FAPA–MS in the offline mode, i.e. desorption and ionization of the analytes from surfaces. Experiments in both positive and negative ion mode revealed ionization patterns for a variety of compound classes comprising alkanes, alcohols, aldehydes, ketones, carboxylic acids, organic peroxides, and alkaloids. Besides the always emphasized detection of quasimolecular ions, a broad range of signals for adducts and losses was found. Additionally, the capabilities and limitations of the technique were studied in three proof-of-principle applications. In general, the method showed to be best suited for polar analytes with high volatilities and low molecular weights, ideally containing nitrogen- and/or oxygen functionalities. However, for compounds with low vapor pressures, containing long carbon chains and/or high molecular weights, desorption and ionization is in direct competition with oxidation of the analytes, leading to the formation of adducts and oxidation products which impede a clear signal assignment in the acquired mass spectra. Nonetheless, FAPA–MS showed to be capable of detecting and identifying common limonene oxidation products in secondary OA (SOA) particles on a filter sample and, thus, is considered a suitable method for offline analysis of OA particles. In the second as well as the subsequent parts, FAPA–MS was applied online, i.e. for real time analysis of OA particles suspended in air. Therefore, the acronym AeroFAPA–MS (i.e. Aerosol FAPA–MS) was chosen to refer to this method. After optimization and characterization, the method was used to measure a range of model compounds and to evaluate typical ionization patterns in the positive and the negative ion mode. In addition, results from laboratory studies as well as from a field campaign in Central Europe (F–BEACh 2014) are presented and discussed. During the F–BEACh campaign AeroFAPA–MS was used in combination with complementary MS techniques, giving a comprehensive characterization of the sampled OA particles. For example, several common SOA marker compounds were identified in real time by MSn experiments, indicating that photochemically aged SOA particles were present during the campaign period. Moreover, AeroFAPA–MS was capable of detecting highly oxidized sulfur-containing compounds in the particle phase, presenting the first real-time measurements of this compound class. Further comparisons with data from other aerosol and gas-phase measurements suggest that both particulate sulfate as well as highly oxidized peroxyradicals in the gas phase might play a role during formation of these species. Besides applying AeroFAPA–MS for the analysis of aerosol particles, desorption processes of particles in the afterglow region were investigated in order to gain a more detailed understanding of the method. While during the previous measurements aerosol particles were pre-evaporated prior to AeroFAPA–MS analysis, in this part no external heat source was applied. Particle size distribution measurements before and after the AeroFAPA source revealed that only an interfacial layer of OA particles is desorbed and, thus, chemically characterized. For particles with initial diameters of 112 nm, desorption radii of 2.5–36.6 nm were found at discharge currents of 15–55 mA from these measurements. In addition, the method was applied for the analysis of laboratory-generated core-shell particles in a proof-of-principle study. As expected, predominantly compounds residing in the shell of the particles were desorbed and ionized with increasing probing depths, suggesting that AeroFAPA–MS might represent a promising technique for depth profiling of OA particles in future studies.