| 1. |
- Azeem, Hafiz Abdul, et al.
(author)
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Extending the scope of dispersive liquid–liquid microextraction for trace analysis of 3-methyl-1,2,3-butanetricarboxylic acid in atmospheric aerosols leading to the discovery of iron(III) complexes
- 2019
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In: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 411:13, s. 2937-2944
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Journal article (peer-reviewed)abstract
- 3-Methyl-1,2,3-butanetricarboxylic acid (MBTCA) is a secondary organic aerosol and can be used as a unique emission marker of biogenic emissions of monoterpenes. Seasonal variations and differences in vegetation cover around the world may lead to low atmospheric MBTCA concentrations, in many cases too low to be measured. Hence, an important tool to quantify the contribution of terrestrial vegetation to the loading of secondary organic aerosol may be compromised. To meet this challenge, a dispersive liquid–liquid microextraction (DLLME) method, known for the extraction of hydrophobic compounds, was extended to the extraction of polar organic compounds like MBTCA without compromising the efficiency of the method. The extraction solvent was fine-tuned using tri-n-octyl phosphine oxide as additive. A multivariate experimental design was applied for deeper understanding of significant variables and interactions between them. The optimum extraction conditions included 1-octanol with 15% tri-n-octyl phosphine oxide (w/w) as extraction solvent, methanol as dispersive solvent, 25% NaCl dissolved in 5 mL sample (w/w) acidified to pH 2 using HNO 3 , and extraction time of 15 min. A limit of detection of 0.12 pg/m 3 in air was achieved. Furthermore, unique complexation behavior of MBTCA with iron(III) was found when analyzed with ultra-high-performance liquid chromatography coupled with electrospray ionization–quadrupole time-of-flight mass spectrometry (UHPLC–ESI–QToF). A comprehensive overview of this complexation behavior of MBTCA was examined with systematically designed experiments. This newly discovered behavior of MBTCA will be of interest for further research on organometallic photooxidation chemistry of atmospheric aerosols. [Figure not available: see fulltext.].
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| 2. |
- Engqvist, Anders, et al.
(author)
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Flow regimes and long-term water exchange of the Himmerfjarden estuary
- 2009
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In: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 83:2, s. 159-174
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Journal article (peer-reviewed)abstract
- A numerical model of processes determining the water exchange encountered in Baltic coastal archipelagos is calibrated and validated against salinity and temperature field data spanning two decades with approximately bi-weekly resolution assessed in the Himmerfjärden estuary. This area is resolved into 17 basins interconnected by 38 individual straits of varying geometrical properties using GIS-based methods. All formulations of the strait exchange flows are free from parameters that need calibration and permit computations of the flow through a strait contraction with or without a coincident sill under a flow classification scheme, of which the first one (a) consists of two groups of multiple layers including aspirated layers from levels beneath the sill crest. The other regimes are as follows. (b) Pure barotropic flow; (c) rotationally controlled flow and (d) plug-flow, which serves as resort solution for flow situations that cannot be solved with (a) and also for computation of the barotropic part of the total flow. For long canals where friction effects act to reduce the flow, a fifth exchange regime is used. The vertical mixing formulation is based on energy balances between supplied wind energy and its work against buoyancy forces. The values of semi-empirical parameters involved in the mixing scheme have been established by calibration against measured data of the first decade period. A statistical evaluation is performed comparing the model results with the measurements of the second decade. It is found that the accuracy of the model is yet limited by the poor temporal resolution in the boundary and the thermal forcing. The overall accuracy of this approach is found to be comparable to earlier model studies in the same area. Since the exchange flows are now based on first principles and are applied to four times more basins, it seems that this more articulated model approach can confidently be applied to more complex archipelago areas.
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| 3. |
- Engqvist, A., et al.
(author)
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Modelling the effects of a pumping program for increasing water circulation in a semi-enclosed bay in the Stockholm archipelago
- 2006
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In: Proceedings of the International Conference on Estuarine and Coastal Modeling. - Reston, VA : American Society of Civil Engineers. - 0784408769 - 9780784408766 ; , s. 253-269
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Conference paper (peer-reviewed)abstract
- Brunnsviken in the inner Stockholm archipelago, close to the City of Stockholm and popular for recreational activities, is a semi-enclosed bay with a very narrow passage to the adjacent archipelago and consequently has a limited water exchange. Various attempts have been made over the past three decades to improve the water quality in the bay. Since 1986, the drinking water authorities of Stockholm withdraw bottom water by pumping it from one of the deep basins of the bay through a pipe to be eventually discharged into the nearest embayment of the archipelago. There are, however, some questions regarding the cost-benefit aspect of this strategy. In particular, it is unclear if the location and the rate of pumping are well chosen in order to increase the ventilation of the bay at large. In addition, it should be possible to eventually optimize the pumping schedule, so that these energy-demanding and thus costly efforts are concentrated to times when they act in concert with natural forcing to increase water exchange. To help improve the pumping program, a modelling project was started in spring 2004. First, a one-dimensional (1-D) layer model that resolves the bay into one basin with multiple-layer stratification was attempted. Second, a three-dimensional (3-D) model with the capacity to be run under non-hydrostatic assumptions was set up at high resolution to study a number of scenarios. Both models were forced by wind, river discharge, surface temperature and the exchange driven by density fluctuations across the boundary to the adjacent archipelago. In the 3-D model, the pumping is included as a virtual divergence of the flow at the location of the pipe. The main results are that the 1-D model performs considerably better than the 3-D model in simulating the measured salinity profiles, even though it does not resolve the basin in the horizontal direction. The poor performance of the 3-D model with regard to salinity is however mainly due to boundary problems: too little inflow of saline water through the narrow and shallow entrance channel, and underestimation of the freshwater supply. The dynamics of the thermocline is better captured by the 3-D model but can certainly also be improved.
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| 4. |
- Genberg, Johan, et al.
(author)
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Radiocarbon and hydrocarbon analysis of pm sources during whtc tests on a biodiesel-fueled engine
- 2014
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; 1
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Conference paper (peer-reviewed)abstract
- PM in diesel exhaust has been given much attention due to its adverse effect on both climate and health. As the PM emission levels are tightened, the portion of particles originating from the lubrication oil is likely to increase. In this study, exhausts from a biodiesel-fueled Euro 5 engine were examined to determine how much of the carbonaceous particles that originated from the fuel and the lubrication oil, respectively. A combination of three methods was used to determine the PM origin: chain length analysis of the hydrocarbons, determination of organic and elemental carbon (OC and EC), and the concentration of 14C found in the exhausts. It was found that the standard method for measuring hydrocarbons in PM on a filter (chain length analysis) only accounted for 63 % of the OC, meaning that it did not account for all non-soot carbon in the exhausts. Comparing the chain length method to the 14C-based method showed that the non-extractable organic carbon originated both from the oil and fuel. Elemental carbon (EC), also known as soot, was found to originate mainly from the fuel. However, excessive amounts of oil in the engine cylinders increased the relative contribution from the oil as well as the absolute emissions of EC. This could either be due to the surplus oil forming soot, or to the soot particles being coated by oil and thereby less efficiently oxidized during the late cycle. The results demonstrate the importance of carefully regulating the amount of lubrication oil reaching the cylinder.
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| 7. |
- Stenström, Petter, et al.
(author)
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Enlarging the undersized spillway of Höljes dam
- 2011
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Conference paper (peer-reviewed)abstract
- Höljes dam is one of the largest embankment dams in Sweden. Studies have shown that it suffers from several deficiencies that would jeopardize the safety of the dam during extreme floods. The major deficiencies include insufficient spillway discharge capacity in relation to the updated design flood and potential risk of erosion in the dam toe in case of large spillway discharges. To safely pass the higher design flood, four major rehabilitation options are evaluated with the help of hydraulic model tests. Option 1 refers to the use of the existing spillway in combination with extra water storage above the full reservoir retention level (FRRL). Option 2 includes construction of a new, separate tunnel spillway. In Option 3, a new gated spillway, 17 m in width, is added to the right of the existing one. Option 4 refers to construction of a new spillway in the form of a 155 m long overflow weir in the reservoir in combination with moderate storage above the FRRL. In Option 1 and 2, the width of the existing spillway channel remains the same and the stilling basin is enlarged, while in Option 3 and 4, the spillway channel is widened and the stilling basin volume is also increased. This paper addresses the advantages and disadvantages of those options. Together with other investigations, hydraulic model testing provides necessary basis for finalization of each design option in terms of spillway discharge capacity and waterway configuration. After weighing the pros and cons, the dam owner has chosen Option 3 as the final rehabilitation alternative. Further investigations are made to optimize the design.
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| 8. |
- Stenström, Petter, 1971-
(author)
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Exchange flows in estuaries and archipelagos
- 2003
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Doctoral thesis (other academic/artistic)abstract
- Different aspects of the exchange of water and tracersbetween adjacent coastal basins, and between the coast and thesea, are addressed. Deviations from the inviscid hydraulicprediction of flow rates and interface heights in maximaltwo-layer exchange flows due to viscous effects are quantifiedby means of non-hydrostatic, three-dimensional numericalmodeling. Simulations are made for different strait geometriesand with a time-dependent barotropic flow to determine when andwhere vertical mixing and the resulting recirculation oftracers preferentially take place (Paper I). Non-hydrostaticthree-dimensional numerical modeling is also performed to studythe variability in circulation and stratification in a tidallyinfluenced estuary. In particular, two processes that act todecrease the rate of flushing of tracers are addressed–turbulent mixing and secondary circulation, i.e. circulationperpendicular to the longitudinal estuary axis (Paper II).Schemes for modeling water exchange in an archipelago, i.e. ina complex system of basins and interconnecting straits, arediscussed (Paper III). Problems relating to Bernoulliaspiration of dense water from below the sill crest,multi-layer stratification, and to some extent rotationalcontrol in parallel straits are addressed.Methodological aspects of both three dimensional numericalmodeling and of solution of the inviscid two-layer straitexchange problem are discussed. In the three-dimensionalnumerical modeling two issues are central: (i) theimplementation of open boundary conditions that allow a meanflow to be forced from one of the boundaries, while at the sametime let barotropic and baroclinic waves be radiated out of thedomain with minimum reflection, and (ii) the implementation ofa subgrid closure scheme to calculate the vertical eddyviscosity and diffusivity coefficients locally fromresolved-scale shear and stratification.
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| 9. |
- Stenström, Petter
(author)
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Hydraulics and mixing in the Hudson River estuary : A numerical model study of tidal variations during neap tide conditions
- 2004
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 109:C4, s. C04019-
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Journal article (peer-reviewed)abstract
- Three-dimensional numerical modeling is performed to study intratidal and along-channel variability in stratification and mixing in the Hudson River estuary. The modeled fields show good agreement with observations, both qualitatively and quantitatively. Estuarine circulation dominates the mean fields, and intratidal variability is dominated by tidal straining that acts to strengthen the stratification during ebb and weaken it during flood. Mixing is mainly confined to a bottom layer during flood but occurs higher up in the water column during ebb. Mixing across the halocline shows marked along-channel variability due to bathymetric effects. During ebb, mixing occurs preferentially at an abrupt channel expansion seaward of a channel constriction at the George Washington Bridge, as predicted by Chant and Wilson [2000]. The salt flux across the halocline in this region, averaged over ebb, exceeds 5x10(-4) kg m(-2) s(-1), a factor of 3 greater than the along-channel average. Increased residence time of tracers should be expected in this region due to the strong mixing but also due to observed secondary circulation [Chant and Wilson, 1997]. Mixing across the halocline during flood is small, except for early flood, before the well-mixed bottom layer is developed. Mixing is then localized to the landward slope of sills.
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| 10. |
- Stenström, Petter, et al.
(author)
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Increasing the discharge capacity at the Höljes dam in Klarälven, Sweden
- 2009
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Conference paper (peer-reviewed)abstract
- The Höljes dam was constructed during 1959-62 and is one of Sweden’s largest embankment dams, with a height of 80 m. The dam is classified in the highest category with regard to dam break consequences. There are three spillways: one bottom outlet, one primary spillway and one log flume. Their discharge capacity at full reservoir level is 185 m3/s, 1290 m3/s and 120 m3/s, respectively. The function of the spillways at full discharge has however been questioned. Two issues are of particular concern: (i) The stilling basin at the end of the chute from the primary spillway was originally designed for a discharge of less than 900 m3/s, and is now in poor condition. One of the concerns is whether the walls of the stilling basin could collapse at high discharge, which could lead to accelerating erosion towards the dam toe. (ii) The discharge from the bottom outlet is conveyed via the old diversion tunnel, in which a hydraulic jump occurs. There is a risk that the diversion tunnel outlet may be inundated at the design flood. The free aeration for the hydraulic jump would then be cutoff, which could lead to large-scale air pulsations and dangerous shock pressures. The design flood has also been questioned and recent recalculations give a 20-30 % increase in the design flood. During 2008, different measures are evaluated for increasing the discharge capacity so as to safely pass a higher design flood. Initially, three alternatives will be analyzed through hydraulic model tests:
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