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This study provides the first comprehensive overview of the sustainability performance of the hotel sector in the Himalayan region: Sagarmatha National Park and Buffer Zone, using both environmental, economic, and technical criteria. In particular, the performance of 45 buildings in this region were measured and quantified in terms of life cycle based carbon footprint, life cycle costs, heat loss rate, number of guests, energy consumption, and area. Buildings were classified into three types: traditional, semi-modern and modern. The statistical analysis included testing for significant differences between such categories by means of ANOVA, and determination of the correlation between the same parameters. Results show a significant difference between the buildings’ total carbon footprint and operation stage carbon footprint while, there is no significant difference between the buildings’ life cycle costs. Traditional buildings have on average the largest carbon footprint and life-cycle cost over the typical building lifespan of 50 years of building lifespan. The ANOVA tests highlight how heat loss rate, size of the building and number of tourists in the hotels are significantly different across the building types. A strong positive correlation is observed between environmental impact, economic impact and energy consumption for the household activities, and a negative correlation with the number of guests and building size. By considering several buildings, this study allows to draw new and more general conclusions about effective sustainability strategies in the whole hotel sector in the Himalayan region. In particular, it shows that reducing impacts in the operation stage should be highly prioritized, focusing on reducing energy consumption and heat loss and shifting to the use of renewable energy sources.

Formate production via both CO2 reduction and cellulose oxidation in a solar-driven process is achieved by a semiartificial biohybrid photocatalyst consisting of immobilized formate dehydrogenase on titanium dioxide (TiO2|FDH) producing up to 1.16±0.04 mmolformate gTiO2-1 in 24 hours. Isotopic labelling experiments with 13C-labelled substrates support the mechanism of stoichiometric formate formation through both redox half-reactions. TiO2|FDH was further immobilized on hollow glass microspheres to perform more practical floating photoreforming allowing vertical solar light illumination with optimal light exposure of the photocatalyst to real sunlight. Enzymatic cellulose depolymerization coupled to the floating photoreforming catalyst generates 0.36±0.04 mmolformate mirr-2 after 24 h. This work thus presents simultaneous solar-driven valorization of waste streams, demonstrates the advantages of biohybrid photocatalysts in photoreforming for the first time and will provide inspiration for the development of future semi-artificial waste-to-chemical conversion strategies.

One of the biggest challenges in converting wave energy is to enable the use of low frequency waves, since the highest waves in typical sea states have low frequencies, as can be seen from the corresponding wave spectra, such as the Pierson–Moskowitz or JONSWAP spectra. In this paper, we show that this challenge is indeed achievable for the operation of small autonomous drifting sensor platforms. We present the design and optimization of a compact wave energy converter that freely floats in random sea waves. An optimization of the dynamical behavior as well as the electromagnetic power take-off is conducted based on simulations and experiments. The platform has compact dimensions of 50 cm draft and 50 cm diameter, which leads to special requirements for size and appearance. To meet these requirements, a two-body self-reacting point absorber is designed and a flux switching permanent magnet linear machine is developed for the power take-off. The developed system is validated by experiments in a wave flume and the linear generator is analyzed on a test bench. A coupled model is used to simulate and optimize the corresponding mechanical system, which leads to an increased output power from below 10 mW for the simulated initial setup to a power output of more than 100 mW in the simulation. Simulations and experiments are performed for regular and random waves in order to provide realistic approximations of the total output power.

Estimates of wind power potential are relevant for decision-making in energy policy and business. Such estimates are affected by several uncertain assumptions, most significantly related to wind turbine technology and land use. Here, we calculate the technical and economic onshore wind power potentials with the aim to evaluate the impact of such assumptions using the case-study area of Finland as an example. We show that the assumptions regarding turbine technology and land use policy are highly significant for the potential estimate. Modern turbines with lower specific ratings and greater hub heights improve the wind power potential considerably, even though it was assumed that the larger rotors decrease the installation density and increase the turbine investment costs. New technology also decreases the impact of strict land use policies. Uncertainty in estimating the cost of wind power technology limits the accuracy of assessing economic wind power potential.

Over the past decade, lead-halide perovskites (LHPs) have demonstrated significant potential in terms of their performance across a wide range of optoelectronic devices, including solar cells, photodetectors and light-emitting diodes. However, the toxicity of lead and instability issue of LHPs are still concerns for their widespread implementation. These successes, but also the challenges of LHPs have motivated great efforts across multiple disciplines to search for lead-free and stable alternatives that can have similar optoelectronic properties to LHPs, namely ‘perovskite-inspired materials (PIMs)’. With the deeper understanding of defect tolerance displayed in LHPs, a large number of PIMs have been identified until now. Among all the identified PIMs, ternary chalcogenides or ABZ2 materials, are believed to be one of the most promising alternatives so far, owing to their simple fabrication protocols, strong absorption and high stability in air. Particularly, AgBiS2 solar cells have demonstrated the highest efficiency (9.17%) among all bismuth-based solar cells. Nevertheless, studies into ternary chalcogenides are mostly limited to AgBiS2 photovoltaics, and the investigations into other potential ABZ2 materials or broader applications are rare so far. Therefore, this thesis will aim to investigate the optoelectronic properties of another promising while rarely investigated ABZ2 material – NaBiS2, and also the potential of AgBiS2 as near-infrared (NIR) photodetectors. In the first project of this thesis, NaBiS2 nanocrystals (NCs) have been shown to exhibit extremely strong absorption, along with a comparatively sharp absorption onset. However, optical-pump-terahertz-probe (OPTP) measurements indicated that most free charge-carriers in NaBiS2 NCs will be localised within a few picoseconds. These localised charge-carriers only exhibited low mobility of around 0.03 cm2 V-1 s-1 and could not transport effectively even though they might be rather long-lived in NaBiS2 and unaffected by intentionally-introduced defects. With help from density functional theory (DFT) calculations, all of these unusual characteristics in NaBiS2 have been shown to closely associate with intrinsic cation disorder, which was also observed in AgBiS2. Although post-annealing is effective for improving cation inhomogeneity and enhancing absorption in AgBiS2, its effect on NaBiS2 was found to be rather minor, which also indicated that the charge-carrier localisation process in NaBiS2 could not be significantly mitigated after annealing. Based on the fundamental insights acquired in the first project, the possibility of further improving charge-carrier transport in NaBiS2 NCs through ligand exchange treatment was investigated in my second project. Using a variety of correlated spectroscopic characterisation techniques, I found that NaBiS2 NCs treated by inorganic iodide ligands had enhanced sum mobility and surface photovoltage (SPV) signals, which implies an improvement in the macroscopic charge-carrier transport. However, the ultrafast localisation process was still observed in these iodide-treated NaBiS2 NCs, suggesting that their cation disorder was not greatly changed. At the same time, the defect capture rates were also found to be lower in the iodide-treated NaBiS2 NCs based on my two proposed models for describing charge-carrier dynamics. As a result, solar cells based on these iodide-treated NaBiS2 NCs could exhibit a peak external quantum efficiency (EQE) value over 50%, along with a power conversion efficiency exceeding 0.7%. Although this is an order of magnitude larger than previous reports, I found ion migration to be a limiting factor for NaBiS2 devices from temperature-dependent transient current measurements, where a low activation energy of only 88 meV was extracted. In my third project, AgBiS2 photodetectors were fabricated and characterised in depth. Aside from the broadband photo-response across from ultra-violet (UV) to near-infrared (NIR) region, AgBiS2 photodetectors have demonstrated an extremely high cut-off frequency (f-3dB) on MHz order, indicating their great potential in applications requiring fast device response such as optical communications. The mechanism behind this fast response was studied, and a relatively long drift length compared to the AgBiS2 film thickness is believed to be the key reason. Similar to NaBiS2 devices, ion migration was also found easy in AgBiS2 devices with an activation energy of 124 meV, which could lead to their increasing noise currents with time. Importantly, these noise currents could be also effectively suppressed when optimising the AgBiS2 film thickness, in which a balance between large shunt resistant and cumulative quantity of defects should be reached. Finally, owing to the small bandgap of AgBiS2 NCs (~1.2 eV), AgBiS2 photodetectors could effectively monitor the heartbeat rates by probing the transmission change of blood vessels illuminated by NIR light, which has been widely used in the medical field owing to its deeper penetration in tissues. These three projects not only uncovered several remarkable optoelectronic characteristics of ABZ2 materials, but also investigated possible methods to further alter these characteristics. Although ABZ2 materials have shown great potential as light harvesters, it can be seen that both cation disorder (or charge-carrier localisation) and ion migration are still limiting the performance. More studies on the root causes of both phenomena, and how to effectively suppress their effects on the materials, would be hence crucial in the future work. With more understandings on this material class, we could expect more efficient, stable, and cleaner optoelectronic devices to be realised in the future.

AbstractMountain treelines are thought to be sensitive to climate change. However, how climate impacts mountain treelines is not yet fully understood as treelines may also be affected by other human activities. Here, we focus on “closed‐loop” mountain treelines (CLMT) that completely encircle a mountain and are less likely to have been influenced by human land‐use change. We detect a total length of ~916,425 km of CLMT across 243 mountain ranges globally and reveal a bimodal latitudinal distribution of treeline elevations with higher treeline elevations occurring at greater distances from the coast. Spatially, we find that temperature is the main climatic driver of treeline elevation in boreal and tropical regions, whereas precipitation drives CLMT position in temperate zones. Temporally, we show that 70% of CLMT have moved upward, with a mean shift rate of 1.2 m/year over the first decade of the 21st century. CLMT are shifting fastest in the tropics (mean of 3.1 m/year), but with greater variability. Our work provides a new mountain treeline database that isolates climate impacts from other anthropogenic pressures, and has important implications for biodiversity, natural resources, and ecosystem adaptation in a changing climate.

Over the past several years, online disinformation and misinformation concerning climate change have gained substantive attention within the scientific community. However, while the dynamics that drive the circulation of false online information have been analysed extensively, it remains unclear whether (and how) this phenomenon can be counteracted. This research project analyses the emerging role of bottom-up mobilisations as a form of noise-reduction, thereby examining how social movements may deploy peer-produced communication narra- tives to counteract the circulation of online disinformation and misinformation relating to climate change. To investigate this communication dynamic, this research applies techniques from computational social sciences to an original dataset of ≈ 250k Facebook posts produced by two movements that best embody this novel and innovative generation of radical envi- ronmental activism: Extinction Rebellion and Fridays for Future. The central thesis of this project forwards two original contributions to the fields of climate change communication and social movement studies. First, it analyses the emergence of a new generation of radical climate change movements and the significance of this new development in climate activism (Chapter II). Second, it offers interdisciplinary empirical evidence on how radical climate movements can act as a bottom-up force for what I term ‘epistemic activism’. It presents a theoretical framework where activist-led, peer-produced communication can provide a coun- tering force to both vertical disinformation and horizontal misinformation. It quantitatively analyses two channels through which these forms of false information can be opposed. For reducing vertical disinformation, this work assesses the use of naming and shaming against information polluters (Chapter III), while for horizontal misinformation, it evaluates the dissemination of scientific counter-narratives (Chapter IV). Ultimately, this thesis shows that the two movements under analysis engage extensively in epistemic activism, with great potential to influence the online climate change debate positively.

Material supporting the contribution by Bréthaut, Gallagher, Dalton and Allouche to Environmental Science & Policy : Power dynamics and integration in the Water-Energy-Food Nexus: learning lessons for transdisciplinary research in Cambodia (submitted for review, August 2018).