| 3. |
- Larsson, Per-Erik
(författare)
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Modelling Chemical Reactions : Theoretical Investigations of Organic Rearrangement Reactions
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chemical reactions are ubiquitous and very important for life and many other processes taking place on earth. In both theoretical and experimental studies of reactivity a transition state is often used to rationalise the outcome of such studies. The present thesis deals with calculations of transition states in radical cation rearrangements, and a principle of least motion study of the rearrangements in the barbaralyl cation. In particular, alternative quadricyclane radical cation (Q∙+) rearrangements are extensively studied. The rearrangement of Q∙+ to norbornadiene is extremely facile and is often used as a prototype for one-electron oxidations. However, electron spin resonance (ESR) experiments show that there are additional cations formed from Q∙+. Two plausible paths for the rearrangement of Q∙+ to the 1,3,5-cycloheptatriene radical cation are located. The most favourable one is a multistep rearrangement with two shallow intermediates, which has a rate-limiting step of 16.5 kcal/mol. In addition, a special structure, the bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation, is identified on these alternative paths; and its computed ESR parameters agree excellently with the experimental spectrum assigned to another intermediate on this path. Moreover, this cation show a homoconjugative stabilization, which is uncommon for radical cations. The bicyclopropylidene (BCP) radical cation undergoes ring opening to the tetramethyleneethane radical cation upon γ-irradiation of the neutral BCP. This rearrangement proceeds through a stepwise mechanism for the first ring opening with a 7.3 kcal/mol activation energy, while the second ring opening has no activation energy. The dominating reaction coordinate during each ring opening is an olefinic carbon rehybridization. The principle of least motion is based on the idea that, on passing from reactant to product, the reaction path with the least nuclear change is the most likely. By using hyperspherical coordinates to define a distance measure between conformations on a potential energy surface, a possibility to interpret reaction paths in terms of distance arises. In applying this measure to the complex rearrangements of the barbaralyl cation, a correct ordering of the conformations on this surface is found.
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| 4. |
- Ytreberg, Erik, 1980, et al.
(författare)
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EMERGE deliverable 6.1. Baltic and North Sea report
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Shipping is responsible for a range of different pressures affecting air quality, climate, and the marine environment. However, most social and economic analysis of shipping have focused on air pollution assessment and how shipping may impact climate change and human health. This risks policies to be biased towards air pollution and climate change, while trading off impacts on the marine environment. One example is the IMO’s global sulphur cap, which requires shipowners to use a compliant fuel with a sulphur content of 0.5% (0.1% in SECA regions) or use alternative compliance options (scrubbers) that are effective in reducing sulphur oxide (SOX) emissions to the atmosphere. The scrubber process results in large volumes of acidic discharge water. Although regulations primarily target SOX removal, other pollutants such as polycyclic aromatic hydrocarbons (PAHs) and metals are transferred from the exhausts to the wash water and subsequently discharged to the marine environment. The aim of this deliverable has therefore been to develop a holistic framework to evaluate the impacts of shipping emissions, particularly those related to scrubbers, on the marine environment, human health, climate, and economy. The structure of this deliverable follows the well-established DAPSIR (Driver-Activity-Pressure-State-Impact-Response) framework, under which information, findings and conclusions from previous work packages are synthesized and integrated, including experiments of direct emissions from shipping to the marine environment (WP2) and the atmosphere (WP3), assessment of marine environmental impacts (WP2, WP4 and WP6), as well as human health and climate change impacts (WP5 and WP6). Finally, this deliverable provides recommendations and guidance for stakeholders and policymakers. The assessment is performed using a baseline scenario (year 2018) and three future scenarios (for year 2050) based on different projected future developments of shipping transport volumes and considering the development of ships regarding fuel efficiency and ship size. In this deliverable, we focused primarily on two of the different future scenarios, scenario 3 (high scrubber pressure) and scenario 8 (high use of liquefied natural gas (LNG) and methanol). The marine environmental risk assessment, performed in the Öresund region for the baseline scenario (2018), showed unacceptable risks when ships in the area were using open loop scrubbers. In the assessment, modelled predicted environmental concentrations (PECs) of open loop scrubber discharge water exceeded the tolerable marine threshold value (predicted no-effect concentration, PNEC) in almost the entire Öresund region. The PEC value was derived based on ship activity and discharges of scrubber water in 2018, while the PNEC value was derived based on the ecotoxicological assays performed within the EMERGE project. Notably, the modelling of open loop scrubber discharge water was performed using the ship traffic activity in 2018 when less than 200 ships in the Baltic Sea used scrubbers, collectively releasing 192 million tonnes of discharge water. By 2022 there were approximately 800 ships equipped with scrubbers in the Baltic Sea. In the high scrubber future scenario (S3) in 2050 this led to an assumption of the considerably higher scrubber water discharge (1740 million tonnes), representing almost one order of magnitude higher compared to our baseline scenario in 2018. In addition, our impact assessment, following Marine Environment Protection Committee (MEPC) guidelines, shows that a ban on discharge water from scrubbers should be considered in the entire Baltic and North Sea region, since all sea basins in the region fail to reach good environmental status (GES) as defined by the EU Marine Strategy Framework Directive (Directive 2008/56/EC). However, the costs of such a measure for the shipping sector (banning discharges from scrubbers, i.e., in practice a ban on scrubbers) have been questioned within the International Maritime Organisation (IMO). Therefore, EMERGE also focused on analysing to what extent the global scrubber fleet has reached break-even on their scrubber installations and the potential monetary gain of using Heavy Fuel Oil (HFO) as compared to the more expensive Marine Gas Oil (MGO) or Very Low Sulphur Fuel Oil (VLSFO). Our results showed that 51% of the global scrubber fleet had reached break-even by the end of 2022, resulting in a summarised balance of 4.7 billion €2019. In addition, the marine ecotoxicity damage cost, by not restricting scrubbers in the Baltic Sea Area, accumulated to >680 million €2019 from 2015 to end of 2022. For air quality, both future scenarios showed a decrease in shipping contribution to PM2.5 exposure by a factor of 2 to 3 compared to our baseline scenario in 2018. Scenario 8 is somewhat more efficient in decreasing the shipping originated PM2.5 than scenario 3. Using the Greenhouse gas and Air pollution Interactions and Synergies (GAINS) model for human health impact assessment in scenario 3 revealed the loss of life expectancy in most areas around the Baltic Sea, when considering all sources, to be limited to two to four months. However, the differences in life shortening between Scenarios 3 and 8 are two to three orders of magnitude lower when compared to human health impacts resulting from all sources, indicating that scrubbers alone have a minor impact on human health in the Baltic region from air quality perspective. For Öresund case the shipping-related health impacts from PM2.5 represented approximately 10% of the total burden of air pollution, in 2050 scenario simulations this burden decreased to 7-9%. Important improvement of air quality in the scenario simulations come also from reduction of NO2 which is a criteria pollutant regulated by the Air Quality Directive, where the decrease is 3 to 5-fold. In relative terms the shipping contribution to NO2 concentration levels, however, maintains similar, approximately 25%, as the land emissions are also expected to decrease. The GAINS health impact assessment for the Baltic Sea was compared to the Solent region using a statistical technique. The latter study showed that a relatively small fraction of all premature deaths in Southampton, Portsmouth, Poole, Christchurch & Bournemouth are attributable to air pollution from shipping, corroborating the conclusion that the deployment scrubbers alone has a minor impact on human life shortening through atmospheric transport.
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| 5. |
- Zetterström Evins, Lena
(författare)
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Geochronology of the Oklo and Bangombé fossil natural fission reactors : tracing the effects of geological events
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thesis to be publicly defended for the degree of Doctor of Philosophy, in lecture room De Geersalen, Svante Arrhenius väg 8a, Stockholm, Friday February 1, 2002 at 10.00 am. Two billion years ago, natural fission reactions took place in the Oklo and Bangombé uranium ores in Gabon, West Equatorial Africa. Uraninite (UO 2+x) in the reactor zones is studied as a natural analogue to spent nuclear fuel. Since uraninite accumulates radiogenic Pb, U-Pb isotope systematics may be used to establish when uraninite alteration, and consequently migration of elements contained in the uraninite, occurred. The aim of this study is to establish when uraninite alteration and related radiogenic Pb loss occurred in the Oklo and Bangombé natural fission reactors.The isotopic compositions of U, Pb and S in uraninite, galena (PbS) and zircon (ZrSiO 4) were analysed using an ion microprobe. The ion microprobe technique requires the use of standards of the same mineral as the sample in order to determine instrumental fractionation. One part of this study involved describing and evaluating potential uraninite and galena standards for U and Pb isotopic analysis by ion microprobe. The galena standard analyses showed that Pb isotopic fractionation during galena analyses was ca 0.5% per atomic mass unit (a.m.u.) in favour of the lighter isotope. The uraninite standard study showed that U isotopic fractionation was ca 1.4% per a.m.u. in favour of the lighter isotope and that uraninite ion microprobe analysis may be influenced by significant amounts of hydrides. Hydride interferences during Pb isotopic analysis of uraninite were found to be of greater importance than Pb isotopic fractionation.A dolerite dyke swarm in the Francevillian basin, where the Oklo and Bangombé U deposits are located, was previously dated to sometime between ca 1000 and 700 Ma. In this study, zircon U-Pb ion microprobe analyses of one of the dolerite dykes yielded an age of 860±39 Ma (2). This age is in accordance with single-stage Pb-Pb model ages of large, mm-sized galena crystals that formed during a major Pb loss from uraninite in the reactor zones. Smaller galena crystals, ca 10 µm in diameter, are common in reactor zone 16 at Oklo. Variable Pb isotopic compositions of these crystals indicate that they formed sometime after the ca 860 Ma old major Pb loss from uraninite. An age of ca. 500 Ma is suggested for this second event of Pb loss and galena crystallisation. The existence of a second event of radiogenic Pb loss from uraninite is also indicated by the alteration of dolerite dykes that cross-cut the Oklo deposit. One of these altered dykes contains galena with Pb originating from the uranium ore as well as S from the surrounding sediment. Hence, the galena crystals in the dyke are not magmatic but a result of a later element migration. Pb-Pb and U-Pb systematics of uraninite also indicate that recrystallisation of uraninite occurred sometime between 600 to 500 Ma ago at both Oklo and Bangombé. Thus, this study has shown that at least two episodes of Pb loss from uraninite occurred after the formation of fission reactors; one at ca 860 Ma and one 600-500 Ma ago. Either one of these events might be related to regional Pb mobility in the Francevillian basin.
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