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Abstract: In this work, we propose an extension of this method. Using the Aethalometer model (Sandradewi et al., 2008), BC as a tracer for primary emitted aerosols can be successfully divided into two components – BCff related to the usage of fossil fuels and BCbb emitted from biomass burning. Because the OC/BC ratio is expected to be different for fossil fuels and biomass burning, we can similarly introduce the two components of POC – a fossil fuel-related POCff and a biomass-burning-related POCbb.
Keywords: BC tracer model, secondary organic carbon, black carbon
Published in RUNG: 14.11.2024; Views: 308; Downloads: 1
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Abstract: Lignin, a complex aromatic polymer derived from lignocellulosic biomass, is a renewable resource for the production of aromatic-like chemicals and materials. However, its complex nature, depolymerisation and valorisation remain a major challenge for the bio-based community within biorefinery concepts. For this reason, lignin model compounds have been used to understand and design lignin depolymerisation, but insufficient attention has been paid to linking knowledge between simpler systems and applying it to a more complex problem. The objectives of this thesis were formulated accordingly to address the aforementioned gap in the literature. The objectives included a systematic approach correlating studies of lignin model compounds with lignin. Hydrodeoxygenation, cleavage of the β-O-4 bond and depolymerisation were investigated to evaluate the process- and structure-dependent correlations, effects on product distribution and kinetic parameters. The catalytic reactions were carried out in batch reactor and the conditions were applied and intensified according to the knowledge gained during the experimental work. The liquid samples for monomer yield evaluation were analysed by GC-MS, while the structural characteristics of lignin and oligomeric fragments, e.g. molecular weight, functionality/reactivity and structural features, were examined by SEC, quantitative 31P and 2D-HSQC NMR. Kinetic modelling was performed to determine the kinetic parameters (e.g. kinetic constants and activation energies) describing defunctionalisation, β-O-4 bond cleavage and depolymerisation. The study with monomeric lignin compounds contributed to the understanding of the key parameters leading to condensation during hydrotreatment. The unsaturated alkyl side-chain of eugenol and the reactive hydroxyl groups bound irreversibly and formed the carbonaceous species, while 4-propylphenol and 4-propylguaiacol provided important insights into the contribution of steric hindrances to a favourable reaction mechanism. An initial assessment of β-O-4 cleavage was performed with β-O-4-model compound, 2-phenoxy-1-phenylethanol, and linked to the lignin macromolecule by process- and structure-dependent correlations. Although the lignin model compound lacks the structural complexity of lignin, important insights into possible reaction processes were gained and accurate kinetic parameters were determined. Furthermore, lignin isolated in 50 vol% EtOH/H2O solutions was depolymerised and the optimal reaction conditions were defined at a temperature of 275 °C and a pressure of 1.5 MPa with regard to the product distribution and the changes in the structural characteristics of the corresponding oligomeric fragments. Depolymerisation of lignins isolated in different EtOH/H2O solutions showed the importance of the structural features, especially ethoxylation degree and the content of β-O-4 or α-ethoxylated β-O-4 bonds. A higher ethoxylation degree of lignin reduced its potential to depolymerise and achieve the theoretical monomer yield. Therefore, the structural characteristics of lignin play the main role in designing and prediction of lignin depolymerisation. The thesis represents a systematic approach of increasing the complexity of structures exposed to hydrodeoxygenation and depolymerisation. The approach contributed to incorporating the knowledge gained from less complex model compounds to real lignin samples by tailoring and designing lignin depolymerisation to exploit the potential of lignin for biorefinery concepts.
Keywords: model compounds, hydrodeoxygenation, organosolv lignin, depolymerisation, structural characteristics, kinetic modelling, dissertations
Published in RUNG: 08.11.2024; Views: 332; Downloads: 4
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Abstract: With the help of the one-dimensional random Potts-like model, we study the origins of fine structures observed on differential melting profiles of double-stranded DNA. We theoretically assess the effects of sequence arrangement on DNA melting curves through the comparison of results for random, correlated, and block sequences. Our results re-confirm the smearing out of the fine structure with the increase in chain length for all types of sequence arrangements and suggest that the fine structure is a finite-size effect. We have found that the fine structures on melting curves of chains comprised of blocks with correlations in sequence are more persistent, probably because of increased sequence disorder the blocks introduce. Many natural DNAs show a well-expressed fine structure of melting profiles. Our results for block sequences may suggest the existence of such sequence motifs in natural DNA sequences.
Keywords: disordered systems, DNA melting, Potts model
Published in RUNG: 08.08.2024; Views: 917; Downloads: 3
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Abstract: The lockdown measures implemented worldwide to slow the spread of the COVID–19 pandemic have allowed for a unique real-world experiment, regarding the impacts of drastic emission cutbacks on urban air quality. In this study we assess the effects of a 7-week (23 March–10 May 2020) lockdown in the Greater Area of Athens, coupling in situ observations with estimations from a meteorology-atmospheric chemistry model. Measurements in central Athens during the lockdown were compared with levels during the pre- and post-lockdown 3-week periods and with respective levels in the four previous years. We examined regulatory pollutants as well as CO2, black carbon (BC) and source-specific BC components. Models were run for pre-lockdown and lockdown periods, under baseline and reduced-emissions scenarios. The in-situ results indicate mean concentration reductions of 30–35% for traffic-related pollutants in Athens (NO2, CO, BC from fossil fuel combustion), compared to the pre-lockdown period. A large reduction (53%) was observed also for the urban CO2 enhancement while the reduction for PM2.5 was subtler (18%). Significant reductions were also observed when comparing the 2020 lockdown period with past years. However, levels rebounded immediately following the lift of the general lockdown. The decrease in measured NO2 concentrations was reproduced by the implementation of the city scale model, under a realistic reduced-emissions scenario for the lockdown period, anchored at a 46% decline of road transport activity. The model permitted the assessment of air quality improvements on a spatial scale, indicating that NO2 mean concentration reductions in areas of the Athens basin reached up to 50%. The findings suggest a potential for local traffic management strategies to reduce ambient exposure and to minimize exceedances of air quality standards for primary pollutants.
Keywords: pandemic, urban air pollution, traffic, chemical transport model, TAPM, mapping
Published in RUNG: 10.05.2024; Views: 1365; Downloads: 4
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Abstract: The determination of the energy spectrum features with low systematic uncertainty is crucial for interpreting the nature of cosmic rays. In this study, we conducted a measurement of the energy spectrum at the Pierre Auger Observatory using a surface detector with a calorimetric energy scale indirectly set by a fluorescence detector. The surface detector consists of an array of water-Cherenkov detectors that extends over 3000 km^2 with 1500m spacing. Additionally, two nested arrays of the same kind with 750m and 433m spacing were utilized to lower the energy threshold of the measurements. This contribution presents, for the first time, the spectrum measured with the 433m array, which reduces the energy threshold down to 63 PeV, nearly half the energy at which we previously published a steepening using the 750m array. Our measurements include a characterization of the spectral features of the flux steepening around 230 PeV, known as the second-knee. The study benefits from a nearly 100% duty cycle and geometrical exposure. Notably, this is the first simultaneous measurement of the second knee energy and spectral indexes before and after the break, using a surface detector with an energy scale predominantly independent of air shower simulations and assumptions regarding hadronic interaction models.
Keywords: ultra-high energy cosmic rays, Pierre Auger Observatory, hadronic interaction model, water-Cherenkov detectors
Published in RUNG: 23.01.2024; Views: 1445; Downloads: 5
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