Characterizing agricultural N2O emissions in the U.S. Midwest using a novel top-down approach based on airborne in situ measurements

Distickstoffmonoxid (N2O) ist nach Kohlenstoffdioxid und Methan das drittwichtigste langlebige, anthropogene Treibhausgas und heutzutage die dominante ozonabbauende Substanz in der Stratosphäre. Anthropogene Emissionen, vor allem auf Grund von Düngung landwirtschaftlicher Regionen, haben dazu geführt, dass die atmosphärischen Konzentrationen seit dem Start der Industrialisierung um über 20% auf etwa 334 ppb angestiegen sind. Trotz seiner wichtigen Rolle, wird N2O kaum in den Plänen zur Emissionsreduktion innerhalb des Pariser Abkommens berücksichtigt. Ein Grund dafür ist die unzureichende Charakterisierung regionaler N2O Quellen auf Grund fehlender Messungen und Methodiken, welche für eine gründliche Analyse komplexer N2O Flächenquellen nötig sind. In dieser Arbeit wird die Hypothese untersucht, ob regionale flugzeuggetragene in situ Messungen von N2O geeignet sind, um N2O Emissionen aus landwirtschaftlich intensiv genutzten Regionen zu bestimmen und um neueste Bottom-up-Emissionsinventare zu evaluieren. Hierfür wird ein außergewöhnlicher in situ N2O Datensatz verwendet, welcher im Zuge des Atmospheric Carbon and Transport-America (ACT-America) Projekts bei fünf Flugzeugmesskampagnen in allen vier Jahreszeiten von 2016 bis 2019 über dem östlichen Teil der USA zusammengetragen wurde. Der Datensatz besteht aus hochpräzisen Luftproben und einzigartigen, kontinuierlichen Messungen mit einem Absorptionsspektrometer (Quantum Cascade Laser Spectrometer (QCLS)), welches im Zuge dieser Arbeit für N2O optimiert und bei zwei der fünf Flugzeugmesskampagnen erfolgreich eingesetzt wurde. In Kombination mit WRF (Weather Research and Forecasting model) Simulationen und vorhandenen atmosphärischen Dispersionsrechnungen, werden N2O Emissionen im Bottom-up-Inventar EDGAR (Emissions Database for Global Atmospheric Research) skaliert, um so die Emissionen aus dem mittleren Westen der USA (MW) - einer Region mit einer der intensivsten Landwirtschaften weltweit - zu quantifizieren. Mit den QCLS Messungen und WRF Simulationen sind die N2O Emissionen im MW im Oktober 2017 (0.42+-0.28 nmol m-2 s-1) und im Juni/Juli 2019 (1.06+-0.57 nmol m-2 s-1) quantifiziert worden. Die Luftproben, die für alle fünf ACT-America Kampagnen verfügbar sind, wurden verwendet, um die Saisonalität der Emissionen zu untersuchen. Hauptsächlich auf Grund von Düngung, hat diese Studie für den Frühling 75% und für den Herbst 13% höhere Emissionen ergeben als für den Sommer. Emissionsabschätzungen für den Winter waren höchstwahrscheinlich auf Grund von Frost/Tau Zyklen des Bodens sogar 230% höher als für den Sommer. Die Ergebnisse sind konsistent mit anderen bodengebundenen Top-down-Studien, jedoch sind weitere Studien nötig um die Komplexität von N2O Emissionen komplett abbilden zu können. Vergleiche mit dem Bottom-up-Inventar EDGAR haben gezeigt, dass EDGAR N2O Emissionen im MW deutlich (Faktoren zwischen zwei und zehn) und in extremen Fällen sogar um Faktoren bis zu 20 unterschätzt. Monatliche Emissionsabschätzungen für 2011-2015 mit dem prozessbasierten Modell DayCent (daily time-step version of the CENTURY model) sind signifikant besser als EDGAR (Faktoren zwischen zwei und fünf), da DayCent regionale Besonderheiten, wie Bodenbedingungen und Wetter, berücksichtigt. Eine Sensitivitätsanalyse basierend auf den Luftproben und Dispersionsrechnungen deutet daraufhin, dass die Heterogenität von N2O Bodenemissionen im MW im Sommer vorwiegend mit der Bodentemperatur und im Frühling und Herbst vorwiegend mit der Bodenfeuchte korreliert. Im Winter wird das Bodenemissionsgeschehen durch Frost/Tau Zyklen bestimmt. Für eine umfassende quantitative Analyse sind zusätzlich Simulationen mit einem prozessbasierten Modell nötig. Diese Arbeit zeigt, dass flugzeuggetragene in situ N2O Messungen gut geeignet sind, um regionale N2O Emissionen zu charakterisieren. Dies ist ein wertvoller Beitrag zum Bestreben ein nationales N2O Monitoring System zu entwickeln, die Grundlage für Emissionsreduktionsstrategien, welche dringend benötigt werden um die Ziele des Pariser Abkommens zu erreichen.Nitrous oxide (N2O) is, after carbon dioxide and methane, the third most important long-lived anthropogenic greenhouse gas and nowadays the dominant ozone-depleting substance in the stratosphere. Anthropogenic emissions, mainly released due to fertilization practices in agricultural regions, have increased atmospheric concentrations by more than 20% since the start of the industrialization to about 334 ppb. Despite its important role, N2O is almost ignored in emission reduction plans submitted to the Paris Agreement. One of the reasons for this is the insufficient characterization of regional N2O sources due to the lack of measurements and methodologies required for thorough analyses of complex N2O area sources. This thesis investigates the hypothesis that regional-scale airborne in situ measurements of N2O are well-suited to characterize N2O emissions from intensively cultivated agricultural regions and to evaluate state-of-the-art bottom-up emission inventories. To this end, an exceptional in situ N2O dataset is used, which has been collected in the course of the Atmospheric Carbon and Transport-America (ACT-America) project (2016-2019) during five aircraft campaigns covering all four seasons over the eastern part of the U.S. It consists of high-precision flask measurements and unique continuous measurements with an absorption spectrometer (Quantum Cascade Laser Spectrometer (QCLS)), which, in the course of this work, was optimized for N2O and successfully deployed during two of the five aircraft campaigns. In combination with WRF (Weather Research and Forecasting model) simulations and available atmospheric dispersion calculations, N2O emissions in the bottom-up inventory EDGAR (Emissions Database for Global Atmospheric Research) are scaled to quantify emissions from the U.S. Midwest - a region with one of the most intensive agriculture in the world. Using a combination of QCLS measurements and WRF simulations, N2O emissions in the Midwest in October 2017 (0.42+-0.28 nmol m-2 s-1) and June/July 2019 (1.06+-0.57 nmol m-2 s-1) have been quantified. Flask measurements, available for all five ACT-America deployments, were further used to study the seasonality of emissions. Primarily due to fertilization, emissions in spring were found to be 75% higher than in summer, while in fall, they were observed to be 13% higher than in summer. In winter, estimated emissions even exceeded the summer estimates by 230%, most likely due to freezing/thawing processes of the soils. The results of this study are consistent with other ground-based top-down studies. However, further studies are needed to be able to fully capture the complexity of N2O emissions. Comparisons with the bottom-up inventory EDGAR show that EDGAR underestimates Midwest N2O emissions significantly (factors between two and ten), for exceptional cases even by factors up to 20. Monthly Midwest emission estimates for 2011-2015 calculated with the process-based model DayCent (daily time-step version of the CENTURY model) are significantly closer to the results of this thesis than EDGAR (factors between two and five), since DayCent considers regional characteristics like soil conditions and weather. A sensitivity analysis using the flask measurements and dispersion calculations indicates that the heterogeneity of N2O soil emissions in the Midwest mainly correlates with soil temperature in summer and soil moisture in spring and fall. In winter, soil emissions are dominated by freezing/thawing processes. For a thorough quantitative analysis, additional simulations with a process-based model are required. This work shows that airborne in situ N2O measurements are suitable for characterizing regional N2O emissions. This is a valuable contribution to the effort to establish a national N2O emission monitoring system, the basis for emission reduction strategies, which are urgently needed to meet the targets of the Paris Agreement

Quantifying nitrous oxide emissions in the U.S. Midwest: a top‐down study using high resolution airborne in‐situ observations

The densely farmed U.S. Midwest is a prominent source of nitrous oxide (N2O) but top‐down and bottom‐up N2O emission estimates differ significantly. We quantify Midwest N2O emissions by combining observations from the Atmospheric Carbon and Transport‐America campaign with model simulations to scale the Emissions Database for Global Atmospheric Research (EDGAR). In October 2017 we scaled agricultural EDGAR v4.3.2 and v5.0 emissions by factors of 6.3 and 3.5, respectively, resulting in 0.42 nmol m−2 s−1 Midwest N2O emissions. In June/July 2019, a period when extreme flooding was occurring in the Midwest, agricultural scaling factors were 11.4 (v4.3.2) and 9.9 (v5.0), resulting in 1.06 nmol m−2 s−1 Midwest emissions. Uncertainties are on the order of 50 %. Agricultural emissions estimated with the process‐based model DayCent (Daily version of the CENTURY ecosystem model) were larger than in EDGAR but still substantially smaller than our estimates. The complexity of N2O emissions demands further studies to fully characterize Midwest emissions

Versatile 3D-Printed Micro-Reference Electrodes for Aqueous and Non-Aqueous Solutions

While numerous reference electrodes suitable for aqueous electrolytes exist, there is no well-defined standard for non-aqueous electrolytes. Furthermore, reference electrodes are often large and do not meet the size requirements for small cells. In this work, we present a simple method for fabricating stable 3D-printed micro-reference electrodes. The prints are made from polyvinylidene fluoride, which is chemically inert in strong acids, bases, and commonly used non-aqueous solvents. We chose six different reference systems based on Ag, Cu, Zn, and Na, including three aqueous and three non-aqueous systems to demonstrate the versatility of the approach. Subsequently, we conducted cyclic voltammetry experiments and measured the potential difference between the aqueous homemade reference electrodes and a commercial Ag/AgCl-electrode. For the non-aqueous reference electrodes, we chose the ferrocene redox couple as an internal standard. From these measurements, we deduced that this new class of micro-reference electrodes is leak-tight and shows a stable electrode potential

Distinct and stage-specific contributions of TET1 and TET2 to stepwise cytosine oxidation in the transition from naive to primed pluripotency

Cytosine DNA bases can be methylated by DNA methyltransferases and subsequently oxidized by TET proteins. The resulting 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) are considered demethylation intermediates as well as stable epigenetic marks. To dissect the contributions of these cytosine modifying enzymes, we generated combinations of Tet knockout (KO) embryonic stem cells (ESCs) and systematically measured protein and DNA modification levels at the transition from naive to primed pluripotency. Whereas the increase of genomic 5-methylcytosine (5mC) levels during exit from pluripotency correlated with an upregulation of the de novo DNA methyltransferases DNMT3A and DNMT3B, the subsequent oxidation steps turned out to be far more complex. The strong increase of oxidized cytosine bases (5hmC, 5fC, and 5caC) was accompanied by a drop in TET2 levels, yet the analysis of KO cells suggested that TET2 is responsible for most 5fC formation. The comparison of modified cytosine and enzyme levels in Tet KO cells revealed distinct and differentiation-dependent contributions of TET1 and TET2 to 5hmC and 5fC formation arguing against a processive mechanism of 5mC oxidation. The apparent independent steps of 5hmC and 5fC formation suggest yet to be identified mechanisms regulating TET activity that may constitute another layer of epigenetic regulation

In‐Liquid Plasma for Surface Engineering of Cu Electrodes with Incorporated SiO2 Nanoparticles: From Micro to Nano

A robust and efficient route to modify the chemical and physical properties of polycrystalline copper (Cu) wires via versatile plasma electrolysis is presented. Silica (SiO2) nanoparticles (11 nm) are introduced during the electrolysis to tailor the surface structure of the Cu electrode. The influence of these SiO2 nanoparticles on the structure of the Cu electrodes during plasma electrolysis over a wide array of applied voltages and processing time is investigated systematically. Homogeneously distributed 3D coral‐like microstructures are observed by scanning electron microscopy on the Cu surface after the in‐liquid plasma treatment. These 3D microstructures grow with increasing plasma processing time. Interestingly, the microstructured copper electrode is composed of CuO as a thin outer layer and a significant amount of inner Cu2O. Furthermore, the oxide film thickness (between 1 and 70 µm), the surface morphology, and the chemical composition can be tuned by controlling the plasma parameters. Remarkably, the fabricated microstructures can be transformed to nanospheres assembled in coral‐like microstructures by a simple electrochemical treatment.DFG, 327886311, SFB 1316: Transiente Atmosphärendruckplasmen - vom Plasma zu Flüssigkeiten zu FestkörpernDFG, 390874152, EXC 2154: POLiS - Post Lithium Storage Cluster of Excellenc

Source apportionment of methane emissions from the Upper Silesian Coal Basin using isotopic signatures

During the CoMet mission in the Upper Silesian Coal Basin (USCB) ground-based and airborne air samples were taken, and analyzed for the isotopic composition of CH4 to derive the mean signature of the USCB and the source signatures of individual coal mines. Using δ2H signatures, the biogenic emissions from the USCB account for 15–50 % of total emissions, which is underestimated in common emission inventories. This demonstrates the importance of δ2H-CH4 observations for methane source attribution

Atmospheric Carbon and Transport - America (ACT-America) Data Sets: Description, Management, and Delivery

Abstract The ACT‐America project is a NASA Earth Venture Suborbital‐2 mission designed to study the transport and fluxes of greenhouse gases. The open and freely available ACT‐America data sets provide airborne in situ measurements of atmospheric carbon dioxide, methane, trace gases, aerosols, clouds, and meteorological properties, airborne remote sensing measurements of aerosol backscatter, atmospheric boundary layer height and columnar content of atmospheric carbon dioxide, tower‐based measurements, and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over the Central and Eastern United States. We conducted 121 research flights during five campaigns in four seasons during 2016–2019 over three regions of the US (Mid‐Atlantic, Midwest and South) using two NASA research aircraft (B‐200 and C‐130). We performed three flight patterns (fair weather, frontal crossings, and OCO‐2 underflights) and collected more than 1,140 h of airborne measurements via level‐leg flights in the atmospheric boundary layer, lower, and upper free troposphere and vertical profiles spanning these altitudes. We also merged various airborne in situ measurements onto a common standard sampling interval, which brings coherence to the data, creates geolocated data products, and makes it much easier for the users to perform holistic analysis of the ACT‐America data products. Here, we report on detailed information of data sets collected, the workflow for data sets including storage and processing of the quality controlled and quality assured harmonized observations, and their archival and formatting for users. Finally, we provide some important information on the dissemination of data products including metadata and highlights of applications of ACT‐America data sets

Characterizing Agricultural N2O Emissions in the U.S. Midwest Using a Novel Top-Down Approach Based on Airborne In Situ Measurements

Nitrous oxide (N2O) is, after carbon dioxide and methane, the third most important long-lived anthropogenic greenhouse gas and nowadays the dominant ozone-depleting substance in the stratosphere. Anthropogenic emissions, mainly released due to fertilization practices in agricultural regions, have increased atmospheric concentrations by more than 20% since the start of the industrialization to about 334 ppb. Despite its important role, N2O is almost ignored in emission reduction plans submitted to the Paris Agreement. One of the reasons for this is the insufficient characterization of regional N2O sources due to the lack of measurements and methodologies required for thorough analyses of complex N2O area sources. This thesis investigates the hypothesis that regional-scale airborne in situ measurements of N2O are well-suited to characterize N2O emissions from intensively cultivated agricultural regions and to evaluate state-of-the-art bottom-up emission inventories. To this end, an exceptional in situ N2O dataset is used, which has been collected in the course of the Atmospheric Carbon and Transport-America (ACT-America) project (2016-2019) during five aircraft campaigns covering all four seasons over the eastern part of the U.S. It consists of high-precision flask measurements and unique continuous measurements with an absorption spectrometer (Quantum Cascade Laser Spectrometer (QCLS)), which, in the course of this work, was optimized for N2O and successfully deployed during two of the five aircraft campaigns. In combination with WRF (Weather Research and Forecasting model) simulations and available atmospheric dispersion calculations, N2O emissions in the bottom-up inventory EDGAR (Emissions Database for Global Atmospheric Research) are scaled to quantify emissions from the U.S. Midwest - a region with one of the most intensive agriculture in the world. Using a combination of QCLS measurements and WRF simulations, N2O emissions in the Midwest in October 2017 (0.42+-0.28 nmol m-2 s-1) and June/July 2019 (1.06+-0.57 nmol m-2 s-1) have been quantified. Flask measurements, available for all five ACT-America deployments, were further used to study the seasonality of emissions. Primarily due to fertilization, emissions in spring were found to be 75% higher than in summer, while in fall, they were observed to be 13% higher than in summer. In winter, estimated emissions even exceeded the summer estimates by 230%, most likely due to freezing/thawing processes of the soils. The results of this study are consistent with other ground-based top-down studies. However, further studies are needed to be able to fully capture the complexity of N2O emissions. Comparisons with the bottom-up inventory EDGAR show that EDGAR underestimates Midwest N2O emissions significantly (factors between two and ten), for exceptional cases even by factors up to 20. Monthly Midwest emission estimates for 2011-2015 calculated with the process-based model DayCent (daily time-step version of the CENTURY model) are significantly closer to the results of this thesis than EDGAR (factors between two and five), since DayCent considers regional characteristics like soil conditions and weather. A sensitivity analysis using the flask measurements and dispersion calculations indicates that the heterogeneity of N2O soil emissions in the Midwest mainly correlates with soil temperature in summer and soil moisture in spring and fall. In winter, soil emissions are dominated by freezing/thawing processes. For a thorough quantitative analysis, additional simulations with a process-based model are required. This work shows that airborne in situ N2O measurements are suitable for characterizing regional N2O emissions. This is a valuable contribution to the effort to establish a national N2O emission monitoring system, the basis for emission reduction strategies, which are urgently needed to meet the targets of the Paris Agreement

An Electrochemical Route for Hot Alkaline Blackening of Steel: A Nitrite Free Approach

Blackening belongs to the predominant technological processes in preserving steel surfaces from corrosion by generating a protective magnetite overlayer. In place of the commonly used dipping-procedure into nitrite-containing blackening baths at boiling temperatures that are far above 100 °C, here we describe a more environmentally friendly electrochemical route that operates at temperatures, even below 100 °C. After an investigation of the electrochemical behavior of steel samples in alkaline solutions at various temperatures, the customarily required bath temperature of more than 130 °C could be significantly lowered to about 80 °C by applying a DC voltage that leads to an electrode potential of 0.5−0.6 V vs. Pt. Thus, it was possible to eliminate the use of hazardous sodium nitrite economically and in an optimum way. Electrochemical quantification of the corrosion behavior of steel surfaces that were in contact with 0.1 M KCl solution was carried out by linear sweep voltammetry and by Tafel slope analysis. When comparing these data, even the corrosion rates of conventional blackened surfaces are of the same magnitude as a blank steel surface. This proves that magnetite overlayers represent rather poor protective layers in the absence of additional sealing. Moreover, cyclic voltammetry (CV), atomic force microscopy (AFM), scanning electron microscopy (SEM) and auger electron spectroscopy (AES) characterized the electrochemically blackened steel surfaces