| 1. |
- Dahal, Karna, 1984, et al.
(författare)
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Reviewing the development of alternative aviation fuels and aircraft propulsion systems
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Alternative aviation fuels such as bio-jet fuels, liquid natural gas (LCH4), hydrogen (H2), electro-jet fuels and direct electricity use play an important role in decarbonizing the aviation sector. New aircraft propulsion systems are being developed but low-blending of fuels is possible for some options. It is imperative to understand the technical, environmental and economic performance of the different alternative aviation fuels and the new engine and propulsion technologies for the utilization of these fuels. We have reviewed various literature to map the current status of development on alternative aviation fuels and related aircraft propulsion systems in relation to different perspective such as their cost and technical maturity. There are several challenges related to the design and implementation of the fuels and new propulsion systems. For instance, the volumetric energy content of alternative fuels is lower than the conventional aviation fuels which requires larger fuel storage tanks. Despite the advantageous environmental performance, both the bio-jet and electro-jet fuels are currently not economically competitive. Yet, studies forecast that increased use of alternative aviation fuels is possible after modifications of engines, fuel storage tanks and improvements of the aerodynamics of aircraft and by introducing subsidies and/or carbon taxes on conventional jet fuels.
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| 2. |
- Dahal, Karna, 1984, et al.
(författare)
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Techno-economic review of alternative fuels and propulsion systems for the aviation sector
- 2021
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Ingår i: Renewable and Sustainable Energy Reviews. - : Elsevier BV. - 1879-0690 .- 1364-0321. ; 151
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Forskningsöversikt (refereegranskat)abstract
- Substitution of conventional jet fuel with low-to zero-carbon-emitting alternative aviation fuels is vital for meeting the climate targets for aviation. It is important to understand the technical, environmental, and economic performance of alternative aviation fuels and prospective engine and propulsion technologies for future aircraft. This study reviews alternative fuels and propulsion systems, focusing on costs and technical maturity, and presents conceptual aircraft designs for different aviation fuels. The cost review includes minimum jet fuel selling price (MJFSP) for alternative aviation fuels. Direct operating cost (DOC) is estimated based on the conceptual aircraft designs and the reviewed MJFSP. The DOCs for bio-jet fuel (5.0–9.2 US cent per passenger-kilometer (¢/PAX/km)), fossil and renewable liquefied hydrogen (5.9–10.1 and 8.1–23.9 ¢/PAX/km, respectively), and electro-methane and electro-jet fuel (5.6–16.7 and 9.2–23.7 ¢/PAX/km, respectively) are higher than for conventional jet fuel (3.9–4.8 ¢/PAX/km) and liquefied natural gas (4.2–5.2 ¢/PAX/km). Overall, DOC of renewable aviation fuels is 15–500 % higher than conventional jet fuels. Among the bio-jet fuels, hydroprocessed esters and fatty acids (23–310 $/GJ) and alcohol-to-jet (4–215 $/GJ) pathways offer the lowest MJFSPs. The implementation of alternative fuels in existing aircraft engines and the design and development of appropriate propulsion systems and aircraft are challenging. The overall cost is a key factor for future implementation. Bio-jet fuel is most promising in the near term while hydrogen and electrofuels in the long term. The level of carbon tax on fossil jet fuels needed for the latter options to be competitive depend on the hydrogen production cost.
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| 3. |
- Fröberg, Mats, et al.
(författare)
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Dissolved organic carbon and nitrogen leaching from Scots pine, Norway spruce and silver birch stands in southern Sweden
- 2011
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 262, s. 1742-1747
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Tidskriftsartikel (refereegranskat)abstract
- The effects of three common tree species - Scots pine, Norway spruce and silver birch - on leaching of dissolved organic carbon and dissolved nitrogen were studied in an experimental forest with podzolised soils in southern Sweden. We analyzed soil water collected with lysimeters and modeled water fluxes to estimate dissolved C and N fluxes. Specific UV absorbance (SUVA) was analyzed to get information about the quality of dissolved organic matter leached from the different stands. Under the O horizon, DOC concentrations and fluxes in the birch stands were lower than in the spruce and pine stands; annual fluxes were 21 g m(-2) y(-1) for birch and 38 g m(-2) y(-1) and 37 g C m(-2) y(-1) for spruce and pine, respectively. Under the B horizon, annual fluxes for all tree species ranged between 3 and 5 g C m(-2) y(-1), implying greater loss of DOC in the mineral soil in the coniferous stands than in the birch stands. We did not find any effect of tree species on the quality of the dissolved organic matter, as measured by SUVA, indicating that the chemical composition of the organic matter was similar in leachates from all three tree species. Substantial amounts of nitrogen was leached out of the soil profile at the bottom of the B horizon from the pine and birch stands, whereas the spruce stands seemed to retain most of the nitrogen in the soil. These differences in N leaching have implications for soil N budgets. (C) 2011 Elsevier B.V. All rights reserved.
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| 4. |
- Hansson, Karna, et al.
(författare)
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Amounts of carbon mineralised and leached as DOC during decomposition of Norway spruce needles and fine roots
- 2010
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 42, s. 178-185
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Tidskriftsartikel (refereegranskat)abstract
- Changes in climate or forest management practices leading to increased litter production will most likely cause increased leaching rates of dissolved organic carbon (DOC) from the O horizon. The rhizosphere is often assumed to have a large carbon flux associated with root turnover and exudation. However, little has been done to quantify the amount of DOC originating from root litter. We studied decomposition of fine root and needle litter of Norway spruce (Picea abies) through a combined incubation and leaching experiment in the laboratory using five different litter types: fresh needle litter, aged needles from the litter layer, fresh and dead roots from mineral soil samples, and seven-year-old roots from a previous litterbag study. After respiration measurements, the samples were percolated with artificial throughfall water and DOC and UV absorbance were measured in the leachate. Mineralisation of dissolved organic matter in the leachate and sorption of DOC to ferrihydrite were determined as a measure of DOC ability to be stabilised by iron (hydr)oxide surfaces.The mineralisation rate and DOC production rate of root samples were always lower than that of needle samples. However, root and needle derived dissolved organic matter (DOM) were similar in terms of aromaticity, as indicated by their specific UV absorbance. and ability to be sorbed by ferrihydrite. For seven-year-old roots, a significantly higher fraction of carbon was lost as DOC (30%) than for younger roots (20%). Furthermore, DOM from old roots bound more strongly to ferrihydrite and is mineralised at a lower rate than DOC from younger roots, suggesting that roots at late stages of decomposition, although a small fraction of total litter, significantly contribute to carbon build-up in mineral soils. The slower decomposition rate of roots compared with needles must be taken into account when modelling litter decomposition. (C) 2009 Elsevier Ltd. All rights reserved.
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| 5. |
- Hansson, Karna, et al.
(författare)
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Carbon and nitrogen pools and fluxes above and below ground in spruce, pine and birch stands in southern Sweden
- 2013
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 309, s. 28-35
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Tidskriftsartikel (refereegranskat)abstract
- We synthesised results on soil carbon (C) and nitrogen (N) fluxes and the accumulation of soil organic C and N under adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils and evaluated the different processes involved. C and N budgets were calculated. Spruce stands had larger stocks of C and N in biomass and soil than birch stands, with pine intermediate. The differences in soil stocks were mainly found in the organic layer, whereas differences in the mineral soil were small. The study showed that there is no simple answer to what is causing the differences in soil C and N stocks, because several processes are interacting. Spruce and pine trees had higher biomass and litter production than birch trees, but total litter inputs showed no significant difference between stands, because the rich ground vegetation under pine and birch contributed with substantial litter inputs, in contrast to the poor ground vegetation under spruce. Decomposition rate (per g of C) was markedly higher under birch than under spruce and pine resulting in lower C and N stocks in the organic layer. This effect was amplified by higher abundance and biomass of earthworms, favoured by higher pH and palatable litter under birch. Earthworm bioturbation probably both increased decomposition rate and damaged the ectomycorrhizal network with negative consequences for the formation of mycorrhizal litter and C storage. In conclusion, the direct effects of spruce, pine and birch litter on C and N pools and fluxes were modified by indirect effects of understorey structure, pH and earthworm responses. (C) 2013 Elsevier B.V. All rights reserved.
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| 6. |
- Hansson, Karna, et al.
(författare)
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Differences in soil properties in adjacent stands of Scots pine, Norway spruce and silver birch in SW Sweden
- 2011
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 262, s. 522-530
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Tidskriftsartikel (refereegranskat)abstract
- Soil properties were compared in adjacent 50-year-old Norway spruce, Scots pine and silver birch stands 26 growing on similar soils in south-west Sweden. The effects of tree species were most apparent in the 27 humus layer and decreased with soil depth. At 20–30 cm depth in the mineral soil, species differences 28 in soil properties were small and mostly not significant. Soil C, N, K, Ca, Mg, and Na content, pH, base sat- 29 uration and fine root biomass all significantly differed between humus layers of different species. Since 30 the climate, parent material, land use history and soil type were similar, the differences can be ascribed to 31 tree species. Spruce stands had the largest amounts of carbon stored down to 30 cm depth in mineral soil 32 (7.3 kg C m??2), whereas birch stands, with the lowest production, smallest amount of litterfall and lowest 33 C:N ratio in litter and humus, had the smallest carbon pool (4.1 kg C m??2), with pine intermediate 34 (4.9 kg C m??2). Similarly, soil nitrogen pools amounted to 349, 269, and 240 g N m??2 for spruce, pine, 35 and birch stands, respectively. The humus layer in birch stands was thin and mixed with mineral soil, 36 and soil pH was highest in the birch stands. Spruce had the thickest humus layer with the lowest pH
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| 7. |
- Hansson, Karna, et al.
(författare)
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Fine root longevity and carbon input into soil from below- and aboveground litter in climatically contrasting forests
- 2014
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 326, s. 79-90
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Tidskriftsartikel (refereegranskat)abstract
- The major part of carbon (C) flow into forest soil consists of continually renewed fine roots and aboveground litterfall. We studied the belowground C input from the fine root litter of trees and understorey vegetation in relation to their aboveground litterfall in two Norway spruce (Picea abies L) stands located in northern and southern Finland. The production of fine roots was estimated by using turnover and biomass data from minirhizotrons and soil cores. The foliage litter production of trees was estimated from litter traps, and that of the understorey vegetation from its annual growth and coverage. Finally, we augmented the data with four spruce plots in Sweden in order to study the above- and belowground litter ratios along latitudinal and soil fertility gradients.The fine root biomass of spruce trees per stand basal area was almost double in the northern site compared to the southern site. Furthermore, spruce fine roots in the north persisted significantly longer (97 +/- 2 weeks) than spruce roots in the south (89 +/- 2 weeks) or understorey fine roots at both sites. The annual production of tree foliage litter was higher in the southern stand, but the total amount of litter (including trees and understorey, above- and belowground) was similar at both sites, as was the ratio between the above- and belowground litter production.The role of understorey vegetation was greater in the northern site where it was responsible for 23% and 33% of below- and aboveground litter production, respectively, compared to 11% and 15% in the south. Thus, both below- and aboveground understorey C input is substantial and should be taken into account in ecosystem C cycle models.The regression between the aboveground:belowground litter production-ratio and the C:N-ratio of the organic layer (combined data from Finland and Sweden), showed that the share of belowground litter production increased when site fertility decreased. This shift in the litter production pattern from above-to belowground in the least fertile sites may have an impact on litter C quality and soil C storage. (C) 2014 The Authors. Published by Elsevier B.V.
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| 8. |
- Hansson, Karna
(författare)
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Fine root production and turnover of tree and understorey vegetation in Scots pine, silver birch and Norway spruce stands in SW Sweden
- 2013
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 309, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- Spruce has a higher aboveground production than pine and birch in southern Sweden and this was reflected in larger fine root biomass as well as higher fine root biomass production. The annual tree fine root biomass production (humus and 0-30 cm in mineral soil) was 73, 78 and 284 g m(-2) in pine, birch and spruce stands, respectively. Thicker fine roots tended to live longer. The majority of the fine roots were thinner than 0.5 mm in diameter, with a turnover rate (KM) of 0.4 year(-1). When comparing all fine roots, i.e. all roots 0-2 mm, pine had the highest longevity, 1120 days, compared with 900 days for spruce and 922 days for birch (KM). (C) 2013 Elsevier B.V. All rights reserved.
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| 9. |
- Hansson, Karna
(författare)
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Impact of tree species on carbon in forest soils
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different tree species differ in productivity, litter quality and quantity, canopy structure and nitrogen deposition. Norway spruce (Picea abies), Scots pine (Pinus sylvestris) and birch (Betula pendula and B. pubescens) are the three dominant tree species in Sweden. This thesis compares soil C fluxes and the accumulation of soil organic carbon under adjacent Norway spruce, Scots pine and silver birch stands growing on similar soils and examines the different processes involved. This was achieved mainly through field measurements of carbon pools and fluxes in southern Sweden, combined with respiration and decomposition studies in the laboratory. Soil carbon fluxes and the accumulation of soil organic carbon were found to differ between the three species, with the strongest differences in humus layers between spruce and birch, with pine intermediate. Most carbon was stored in soils in spruce stands. Birch stands had the fastest root turnover and the highest carbon mineralisation rate. Species differences can be explained by differences in tree growth rate and decomposition. The three tree species differed in terms of litter quality, carbon mineralisation, DOC fluxes and fine root turnover.
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| 10. |
- Olsson, Bengt, et al.
(författare)
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Heterotrophic respiration and nitrogen mineralisation in soils of Norway spruce, Scots pine and silver birch stands in contrasting climates
- 2012
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 269, s. 197-205
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Tidskriftsartikel (refereegranskat)abstract
- Different tree species are often associated with different soil properties. Earlier studies have shown that Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.), the two dominant tree species in Fennoscandia, often generate soils with larger carbon (C) and nitrogen (N) pools than silver birch (Betula pendula Roth.). Consequently, we hypothesised that spruce and pine would create soils with slower turnover rates than birch. To test this, C and N pools and C and N mineralisation rates were determined in different soil layers (humus, 0-10 cm, 10-20 cm mineral soil) at two sites with contrasting climatic conditions. One site (Tonnersjoheden) was located in the temperate zone in SW Sweden and one (Kivalo) in the north boreal zone in N Finland. At both sites, experimental plots with the three tree species had been established more than 50 years before the study. Samples from the different soil layers were incubated at 15 C in the laboratory for 30 days, and C and N mineralisation rates were determined. In addition, earthworm abundance was estimated at Tonnersjoheden but not at Kivalo (no sign of bioturbation). At Tonnersjoheden, soil C and N pools (g C or N m(-2)) were ranked spruce > pine > birch. C mineralisation rate (mg CO2-C g(-1) C d(-1)) was higher in the birch plots than in the other plots, but because of larger C pools in the spruce plots, field C mineralisation (g CO2-C m(-2) year(-1)) was higher for spruce than for pine and birch. Field net N mineralisation (80-90 kg N ha(-1) year(-1)) did not differ significantly between tree species, but nitrification rates (mu g NO3-N g-1 C d-1) in the topsoil were higher in the birch plots than in the other plots. The birch plots had larger populations of earthworms and a higher degree of bioturbation than any of the coniferous plots, which probably explains the higher turnover rate of birch soil organic matter (SOM). At Kivalo, C and N soil pools were significantly larger in spruce than in birch plots, and C mineralisation rate was higher in birch and spruce humus than in pine humus. Net N mineralisation rate and annual field net N mineralisation (<4 kg N ha-1 year-1) were estimated to be very low, with no effect of tree species. Thus, the hypothesis of a 'birch effect' was supported at Tonnersjoheden, but only partly at Kivalo. The main difference seemed to be that the earthworms at Tonnersjoheden accelerated SOM decomposition under birch, whereas earthworm stimulation was negligible at Kivalo, probably because of climate-related limitations. (C) 2012 Elsevier B.V. All rights reserved.
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