| 1. |
- Aas, Wenche
(författare)
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Constitution, dynamics and structure of binary and ternary actinide complexes
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stoichiometry, ligand exchange reactions, coordinationgeometry and stability of complexes of type UO2LpFq(H2O)3-n(p= 1–2,q= 1-3), where L is one of the bidentate ligandspicolinate, oxalate, carbonate or acetate have beeninvestigated using single crystal X-ray diffraction, an arrayof19F-,13C-,17O- and1H-NMR techniques and potentiometric titration usingboth F-and H+selective electrodes. The experiments wereperformed in a 1.00 M NaClO4medium. The equilibrium constants were determinedat 25°C while most of the kinetic experiments were done at- 5°C. The equilibrium constants for the stepwise additionof F-to UO2L and UO2L2indicates that the prior coordination of L toU(VI) has a fairly small effect on the subsequent bonding offluoride, except for a statistical effect determined by thenumber of available coordination sites. This indicates thatternary complexes might be important for the speciation andtransport of hexavalent actinides in ground and surface watersystems. A single crystal structure of UO2(picolinate)F32-has been determined showing the same pentagonalbipyramidal symmetry as in aqueous solution studied by NMR. Theexchangeable donor atoms are situated in a plane perpendicularto the linear uranyl group. The complexes show a variety ofdifferent exchange reactions depending on the ligand used. Ithas been possible to quantify external fluoride and the otherligands exchange reactions as well asintra-molecular reactions. This type of detailedinformation has not been observed in aqueous solution before.Water takes a critical part in the exchange mechanism, and whenit is eliminated from the inner coordination sphere a muchslower kinetics can be observed.19F-NMR has showed to be a powerful technique tostudy these reactions, both because of the sensitivity of thisNMR nucleus and also the possibility to observe reactions wherefluoride is not directly involved in the mechanism. TernaryTh(edta)F1-2and (UO2)2(edta)2F1-4have been investigated using1H and19F-NMR. The fluoride complexation to Cm(III) wasstudied using time resolved fluorescence spectroscopy (TRLFS)and the stability constant for the CmF2+complex was determined at 25°C in 1.0 mNaCl.Keywords. Ternary complexes, actinides,dioxouranium(VI), curium(III), thorium(IV), ligand exchange,isomers, NMR, potentiometric titrations, aqueous solution,oxalate, picolinate, acetate, EDTA.
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| 2. |
- Aas, Wenche, et al.
(författare)
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Equilibria and dynamics in binary and ternary uranyl oxalate and acetate/fluoride complexes
- 1999
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Ingår i: Journal of the Chemical Society - Dalton Transactions. - : Royal Society of Chemistry (RSC). - 0300-9246 .- 1364-5447. ; :8, s. 1311-1317
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Tidskriftsartikel (refereegranskat)abstract
- The formation of ternary UO2(ac)pFq2-p-q (p = 1 or 2 and q = 1-3) complexes, and their equilibrium constants were investigated by potentiometric titrations and 19F NMR spectroscopy. The equilibrium constants have been determined from the emf data in a NaClO4 medium at constant sodium concentration, [Na+] = 1.00 M at 25°C, except for the UO2(ac)F32- complex where 19F NMR at -5°C was used. The magnitude of the equilibrium constant for the stepwise addition of fluoride indicates that prior co-ordination of acetate has only a small effect on the subsequent bonding of fluoride. The acetate exchange in the ternary UO2(ac)F32- complex was studied using 19F NMR. Through magnetisation transfer experiments, it was possible to confirm the provisional mechanism from a previous study and also the consistency of the rate constants for the five different exchange pathways required to describe the fluoride exchange. The exchange takes place via the intermediate UO2F3(H2O)2-, indicating that the acetate exchange follows an interchange mechanism with solvent participation in the transition state. The rates and mechanisms of the ligand exchange reactions in UO2(ox)2(H2O)2- and UO2(ac)2(H2O) have been studied using 13C NMR techniques at -5°C. The rate law is v = k-[complex][ligand], and the second order rate constant and the activation parameters for both systems have been determined. The reactions most likely take place through an Eigen-Wilkins type of mechanism, where the first step is a pre-equilibrium of an outer-sphere complex followed by a rate determining exchange of water. The rate constants for the water exchange reactions are very similar to that in UO2(H2O)52+. The information from the binary oxalate system rules out the formation of UO2(ox)2(H2O)2- as an intermediate in the exchange reactions in the previously studied UO2(ox)2F3-, also in this case confirming a previously suggested exchange mechanism. The H+/D+ isotope effects and a linear free energy relationship suggest that the main catalytic effect of H+ on ligand exchange rates is due to the formation of a protonated precursor. Hence, the catalytic effect depends on the basicity of the ligand and the site for the proton attack.
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| 3. |
- Aas, Wenche, et al.
(författare)
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Trends in Air Pollution in Europe, 2000–2019
- 2024
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Ingår i: Aerosol and Air Quality Research. - 2071-1409 .- 1680-8584. ; 24:4
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Tidskriftsartikel (refereegranskat)abstract
- This paper encompasses an assessment of air pollution trends in rural environments in Europe over the 2000–2019 period, benefiting from extensive long-term observational data from the EMEP monitoring network and EMEP MSC-W model computations. The trends in pollutant concentrations align with the decreasing emission patterns observed throughout Europe. Annual average concentrations of sulfur dioxide, particulate sulfate, and sulfur wet deposition have shown consistent declines of 3–4% annually since 2000. Similarly, oxidized nitrogen species have markedly decreased across Europe, with an annual reduction of 1.5–2% in nitrogen dioxide concentrations, total nitrate in the air, and oxidized nitrogen deposition. Notably, emission reductions and model predictions appear to slightly surpass the observed declines in sulfur and oxidized nitrogen, indicating a potential overestimation of reported emission reductions. Ammonia emissions have decreased less compared to other pollutants since 2000. Significant reductions in particulate ammonium have however, been achieved due to the impact of reductions in SOx and NOx emissions. For ground level ozone, both the observed and modelled peak levels in summer show declining trends, although the observed decline is smaller than modelled. There have been substantial annual reductions of 1.8% and 2.4% in the concentrations of PM10 and PM2.5, respectively. Elemental carbon has seen a reduction of approximately 4.5% per year since 2000. A similar reduction for organic carbon is only seen in winter when primary anthropogenic sources dominate. The observed improvements in European air quality emphasize the importance of comprehensive legislations to mitigate emissions.
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| 4. |
- Alastuey, Andres, et al.
(författare)
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Geochemistry of PM10 over Europe during the EMEP intensive measurement periods in summer 2012 and winter 2013
- 2016
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:10, s. 6107-6129
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Tidskriftsartikel (refereegranskat)abstract
- The third intensive measurement period (IMP) organised by the European Monitoring and Evaluation Programme (EMEP) under the UNECE CLTRAP took place in summer 2012 and winter 2013, with PM10 filter samples concurrently collected at 20 (16 EMEP) regional background sites across Europe for subsequent analysis of their mineral dust content. All samples were analysed by the same or a comparable methodology. Higher PM10 mineral dust loadings were observed at most sites in summer (0.5-10aEuro-A mu gaEuro-m(-3)) compared to winter (0.2-2aEuro-A mu gaEuro-m(-3)), with the most elevated concentrations in the southern- and easternmost countries, accounting for 20-40aEuro-% of PM10. Saharan dust outbreaks were responsible for the high summer dust loadings at western and central European sites, whereas regional or local sources explained the elevated concentrations observed at eastern sites. The eastern Mediterranean sites experienced elevated levels due to African dust outbreaks during both summer and winter. The mineral dust composition varied more in winter than in summer, with a higher relative contribution of anthropogenic dust during the former period. A relatively high contribution of K from non-mineral and non-sea-salt sources, such as biomass burning, was evident in winter at some of the central and eastern European sites. The spatial distribution of some components and metals reveals the influence of specific anthropogenic sources on a regional scale: shipping emissions (V, Ni, and SO42-) in the Mediterranean region, metallurgy (Cr, Ni, and Mn) in central and eastern Europe, high temperature processes (As, Pb, and SO42-) in eastern countries, and traffic (Cu) at sites affected by emissions from nearby cities.
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| 5. |
- Björkman, Mats P., et al.
(författare)
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Nitrate dry deposition in svalbard
- 2013
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 65, s. 19071-
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Tidskriftsartikel (refereegranskat)abstract
- Arctic regions are generally nutrient limited, receiving an extensive part of their bio-available nitrogen from the deposition of atmospheric reactive nitrogen. Reactive nitrogen oxides, as nitric acid (HNO3) and nitrate aerosols (p-NO3), can either be washed out from the atmosphere by precipitation or dry deposited, dissolving to nitrate (NO3-). During winter, NO3- is accumulated in the snowpack and released as a pulse during spring melt. Quantification of NO3- deposition is essential to assess impacts on Arctic terrestrial ecology and for ice core interpretations. However, the individual importance of wet and dry deposition is poorly quantified in the high Arctic regions where in-situ measurements are demanding. In this study, three different methods are employed to quantify NO3- dry deposition around the atmospheric and ecosystem monitoring site, Ny-Alesund, Svalbard, for the winter season (September 2009 to May 2010): (1) A snow tray sampling approach indicates a dry deposition of -10.27 +/- 3.84 mg m(-2) (+/- S.E.); (2) A glacial sampling approach yielded somewhat higher values -30.68 +/- 12.00 mg m(-2); and (3) Dry deposition was also modelled for HNO3 and p-NO3 using atmospheric concentrations and stability observations, resulting in a total combined nitrate dry deposition of -10.76 +/- 1.26 mg m(-2). The model indicates that deposition primarily occurs via HNO3 with only a minor contribution by p-NO3. Modelled median deposition velocities largely explain this difference: 0.63 cm s(-1) for HNO3 while p-NO3 was 0.0025 and 0.16 cm s(-1) for particle sizes 0.7 and 7 mm, respectively. Overall, the three methods are within two standard errors agreement, attributing an average 14% (total range of 2-44%) of the total nitrate deposition to dry deposition. Dry deposition events were identified in association with elevated atmospheric concentrations, corroborating recent studies that identified episodes of rapid pollution transport and deposition to the Arctic.
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| 6. |
- Espen Yttri, Karl, et al.
(författare)
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Trends, composition, and sources of carbonaceous aerosol at the Birkenes Observatory, northern Europe, 2001-2018
- 2021
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 21:9, s. 7149-7170
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Tidskriftsartikel (refereegranskat)abstract
- We present 18 years (2001-2018) of aerosol measurements, including organic and elemental carbon (OC and EC), organic tracers (levoglucosan, arabitol, mannitol, trehalose, glucose, and 2-methyltetrols), trace elements, and ions, at the Birkenes Observatory (southern Norway) - a site representative of the northern European region. The OC=EC (2001-2018) and the levoglucosan (2008-2018) time series are the longest in Europe, with OC=EC available for the PM10, PM2:5 (fine), and PM10-2:5 (coarse) size fractions, providing the opportunity for a nearly 2-decade-long assessment. Using positive matrix factorization (PMF), we identify seven carbonaceous aerosol sources at Birkenes: mineraldust- dominated aerosol (MIN), traffic/industry-like aerosol (TRA/IND), short-range-transported biogenic secondary organic aerosol (BSOASRT), primary biological aerosol particles (PBAP), biomass burning aerosol (BB), ammoniumnitrate- dominated aerosol (NH4NO3), and (one low carbon fraction) sea salt aerosol (SS). We observed significant (p < 0:05), large decreases in EC in PM10 (-3:9%yr-1) and PM2:5 (-4:2%yr-1) and a smaller decline in levoglucosan (-2:8%yr-1), suggesting that OC=EC from traffic and industry is decreasing, whereas the abatement of OC=EC from biomass burning has been slightly less successful. EC abatement with respect to anthropogenic sources is further supported by decreasing EC fractions in PM2:5 (-3:9%yr-1) and PM10 (-4:5%yr-1). PMF apportioned 72% of EC to fossil fuel sources; this was further supported by PMF applied to absorption photometer data, which yielded a two-factor solution with a low aerosol ngstr m exponent (AAED0.93) fraction, assumed to be equivalent black carbon from fossil fuel combustion (eBCFF), contributing 78% to eBC mass. The higher AAE fraction (AAED2.04) is likely eBC from BB (eBCBB). Source-receptor model calculations (FLEXPART) showed that continental Europe and western Russia were the main source regions of both elevated eBCBB and eBCFF. Dominating biogenic sources explain why there was no downward trend for OC. A relative increase in the OC fraction in PM2:5 (C3:2%yr-1) and PM10 (C2:4%yr-1) underscores the importance of biogenic sources at Birkenes (BSOA and PBAP), which were higher in the vegetative season and dominated both fine (53 %) and coarse (78 %) OC. Furthermore, 77 %-91% of OC in PM2:5, PM10-2:5, and PM10 was attributed to biogenic sources in summer vs. 22 %- 37% in winter. The coarse fraction had the highest share of biogenic sources regardless of season and was dominated by PBAP, except in winter. Our results show a shift in the aerosol composition at Birkenes and, thus, also in the relative source contributions. The need for diverse offline and online carbonaceous aerosol speciation to understand carbonaceous aerosol sources, including their seasonal, annual, and long-term variability, has been demonstrated.
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| 7. |
- Hellsten, Sofie, et al.
(författare)
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Base cations deposition in Europe
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The support from the Nordic Council of Ministers, the Working Group for Air and Sea Pollution, has significantly contributed to the development of unified calculations of base cation deposition across Europe with the EMEP model. Previous estimates of base cation deposition in Europe have mainly been based on empirical approaches of varying quality depending on country. The results of the model calculations will be used by CLRTAP and EU to assess the need for reduction of emissions of acidifying air pollutants in agreement with the Gothenburg protocol and NEC. The EMEP model has been extended to calculate the deposition of four base cations; calcium (Ca2+), magnesium (Mg2+), potassium (K+) and sodium (Na+). Natural emissions (from sea salt and wind blown dust) as well as anthropogenic emissions (from combustion and industrial processes) have been considered. Base cations are assumed to behave in a similar manner as primary particles in the atmosphere, and hence the transport and deposition of base cations are considered in the same way as primary particles in the EMEP model. The result of the EMEP modelling was compared with wet deposition fluxes derived from the EMEP and ICP-Forest network, and throughfall measurements from the ICP-Forest network, to assess the robustness of the model calculations. This comparison showed encouraging results. However, it was recognised that the EMEP model can be developed further, particularly regarding the estimates of base cation sources, to correctly quantify the base cation deposition in Europe. Furthermore, to provide a confident assessment of the results of the EMEP model, it is of great importance to further develop and improve the measurement methodologies and the methods applied to estimate dry deposition.
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| 8. |
- Karlsson, Per Erik, et al.
(författare)
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Biomass burning in eastern Europe during spring 2006 caused high deposition of ammonium in northern Fennoscandia
- 2013
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 176, s. 71-79
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Tidskriftsartikel (refereegranskat)abstract
- High air concentrations of ammonium were detected at low and high altitude sites in Sweden, Finland and Norway during the spring 2006, coinciding with polluted air from biomass burning in eastern Europe passing over central and northern Fennoscandia. Unusually high values for throughfall deposition of ammonium were detected at one low altitude site and several high altitude sites in north Sweden. The occurrence of the high ammonium in throughfall differed between the summer months 2006, most likely related to the timing of precipitation events. The ammonia dry deposition may have contributed to unusual visible injuries on the tree vegetation in northern Fennoscandia that occurred during 2006, in combination with high ozone concentrations. It is concluded that long-range transport of ammonium from large-scale biomass burning may contribute substantially to the nitrogen load at northern latitudes. (C) 2013 Elsevier Ltd. All rights reserved.
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| 9. |
- Laj, Paolo, et al.
(författare)
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A global analysis of climate-relevant aerosol properties retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories
- 2020
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 13:8, s. 4353-4392
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol particles are essential constituents of the Earth's atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.
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| 10. |
- Lee, Haebum, et al.
(författare)
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Atmospheric new particle formation characteristics in the Arctic as measured at Mount Zeppelin, Svalbard, from 2016 to 2018
- 2020
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:21, s. 13425-13441
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Tidskriftsartikel (refereegranskat)abstract
- We conducted continuous measurements of nanoparticles down to 3 nm size in the Arctic at Mount Zeppelin, Ny Ålesund, Svalbard, from October 2016 to December 2018, providing a size distribution of nanoparticles (3–60 nm). A significant number of nanoparticles as small as 3 nm were often observed during new particle formation (NPF), particularly in summer, suggesting that these were likely produced near the site rather than being transported from other regions after growth. The average NPF frequency per year was 23 %, having the highest percentage in August (63 %). The average formation rate (J) and growth rate (GR) for 3–7 nm particles were 0.04 cm−3 s−1 and 2.07 nm h−1, respectively. Although NPF frequency in the Arctic was comparable to that in continental areas, the J and GR were much lower. The number of nanoparticles increased more frequently when air mass originated over the south and southwest ocean regions; this pattern overlapped with regions having strong chlorophyll a concentration and dimethyl sulfide (DMS) production capacity (southwest ocean) and was also associated with increased NH3 and H2SO4 concentration, suggesting that marine biogenic sources were responsible for gaseous precursors to NPF. Our results show that previously developed NPF occurrence criteria (low loss rate and high cluster growth rate favor NPF) are also applicable to NPF in the Arctic.
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