| 1. |
- Bäckström, Daniel, 1985, et al.
(författare)
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Particle composition and size distribution in coal flames - The influence on radiative heat transfer
- 2015
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 64, s. 70-80
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Tidskriftsartikel (refereegranskat)abstract
- Radiative heat transfer in a 77 kWth swirling lignite flame has been studied. The aim is to characterize different particle types present in a coal flame and to determine their influence on the radiative heat transfer. The study combines extractive particle measurements, radiative intensity measurements and detailed radiation modelling. The size distribution of the extracted particles was measured with a low pressure impactor and some of the size fractions were analysed with SEM–EDX. The measured total radiative intensity is compared with the modelled intensity based on the particle measurements in the same cross-section of the flame. The particle properties were calculated with Mie theory and the gas properties with a statistical narrow-band model. The results show that the contribution of coal/char particles dominates the radiative heat transfer in the investigated cross-section of the flame. The methodology applied in this work shows promising results for characterization of particle radiation in flames of practical size.
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| 2. |
- Boy, M., et al.
(författare)
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Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:3, s. 2015-2061
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Tidskriftsartikel (refereegranskat)abstract
- The Nordic Centre of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change-cryosphere interactions that affect Arctic amplification.
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| 3. |
- Davidsson, Kent, 1967, et al.
(författare)
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Potassium, chlorine, and sulfur in ash, particles, deposits, and corrosion during wood combustion in a circulating fluidized-bed boiler
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 21:1, s. 71-81
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the addition of chlorine and/or sulfur to the fuel on fly ash composition, deposit formation, and superheater corrosion has been studied during biomass combustion in a circulating fluidized-bed boiler. The chlorine (HCl (aq)) and sulfur (SO2 (g)) were added in proportions of relevance for the potassium chemistry. The composition of the bottom and the fly ashes was analyzed. Gas and particle measurements were performed downstream of the cyclone before the convection pass and the flue gas composition was recorded in the stack with a series of standard instruments and an FTIR analyzer. At the position downstream of the cyclone, a deposit probe was situated, simulating a superheater tube. Deposits on the probe and initial corrosion were examined. It is concluded that addition of sulfur and chlorine increases the formation of submicron particles leading to deposition of potassium sulfate and chloride. The results compare well with earlier work based on laboratory-scale experiments concerning effects of chlorine and sulfur on potassium chemistry.
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| 4. |
- Tan, W., et al.
(författare)
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Atmospheric Chemistry of 2-Amino-2-methyl-1-propanol: A Theoretical and Experimental Study of the OH-Initiated Degradation under Simulated Atmospheric Conditions
- 2021
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 125:34, s. 7502-7519
-
Tidskriftsartikel (refereegranskat)abstract
- The OH-initiated degradation of 2-amino-2-methyl-1-propanol [CH3C(NH2)(CH3)CH2OH, AMP] was investigated in a large atmospheric simulation chamber, employing time-resolved online high-resolution proton-transfer reaction-time-of-flight mass spectrometry (PTR-ToF-MS) and chemical analysis of aerosol online PTR-ToF-MS (CHARON-PTR-ToF-MS) instrumentation, and by theoretical calculations based on M06-2X/aug-cc-pVTZ quantum chemistry results and master equation modeling of the pivotal reaction steps. The quantum chemistry calculations reproduce the experimental rate coefficient of the AMP + OH reaction, aligning k(T) = 5.2 x 10(-12) x exp (505/T) cm(3) molecule(-1) s(-1) to the experimental value k(exp,300K) = 2.8 x 10(-11) cm(3) molecule(-1) s(-1). The theoretical calculations predict that the AMP + OH reaction proceeds via hydrogen abstraction from the -CH3 groups (5-10%), -CH2- group, (>70%) and -NH2 group (5-20%), whereas hydrogen abstraction from the -OH group can be disregarded under atmospheric conditions. A detailed mechanism for atmospheric AMP degradation was obtained as part of the theoretical study. The photo-oxidation experiments show 2-amino-2-methylpropanal [CH3C(NH2)(CH3)CHO] as the major gas-phase product and propan-2-imine [(CH3)(2)C=NH], 2-iminopropanol [(CH3)(CH2OH)C=NH], acetamide [CH3C(O)NH2], formaldehyde (CH2O), and nitramine 2-methyl-2-(nitroamino)-1-propanol [AMPNO(2), CH3C(CH3)(NHNO2)-CH2OH] as minor primary products; there is no experimental evidence of nitrosamine formation. The branching in the initial H abstraction by OH radicals was derived in analyses of the temporal gas-phase product profiles to be B-CH3/B-CH2/B-NH2 = 6:70:24. Secondary photo-oxidation products and products resulting from particle and surface processing of the primary gas-phase products were also observed and quantified. All the photo-oxidation experiments were accompanied by extensive particle formation that was initiated by the reaction of AMP with nitric acid and that mainly consisted of this salt. Minor amounts of the gas-phase photo-oxidation products, including AMPNO(2), were detected in the particles by CHARON-PTR-ToF-MS and GCxGC-NCD. Volatility measurements of laboratory-generated AMP nitrate nanoparticles gave Delta H-vap = 80 +/- 16 kJ mol(-1) and an estimated vapor pressure of (1.3 +/- 0.3) x 10(-5) Pa at 298 K. The atmospheric chemistry of AMP is evaluated and a validated chemistry model for implementation in dispersion models is presented.
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| 5. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Carbon dioxide interactions with crystalline and amorphous ice surfaces
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:21, s. 4627-4631
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide interactions with crystalline and amorphous water ice have been studied by time-resolved molecular beam techniques. CO2 collisions at thermal kinetic energies with ice in the temperature range 100-160 K result in efficient trapping on the ice surface followed by desorption. The desorption kinetics on crystalline ice at 100-125 K are well described by the Arrhenius equation with an activation energy of 0.22 +/- 0.02 eV and a preexponential factor of 10(13.32+/-0.57) s(-1). Below 120 K, CO2 populates strongly bonded sites on amorphous ice, resulting in surface residence times on the order of minutes at 100 K, and the desorption data can in this case not be explained by a simple first-order process. The results are compared to previous studies of gas-ice interactions, and the implications for heterogeneous processes in the terrestrial atmosphere are discussed.
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| 6. |
- Bartels-Rausch, Thorsten, et al.
(författare)
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Ice structures, patterns, and processes: A view across the icefields
- 2012
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Ingår i: Reviews of Modern Physics. ; 84:2, s. 885-944
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Forskningsöversikt (refereegranskat)abstract
- From the frontiers of research on ice dynamics in its broadest sense, this review surveys the structures of ice, the patterns or morphologies it may assume, and the physical and chemical processes in which it is involved. Open questions in the various fields of ice research in nature are highlighted, ranging from terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other Solar System bodies and in interstellar space.
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| 7. |
- Castarède, Dimitri, et al.
(författare)
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Development and characterization of the Portable Ice Nucleation Chamber 2 (PINCii)
- 2023
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Ingår i: Atmospheric Measurement Techniques. - 1867-1381. ; 16:16, s. 3881-3899
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Tidskriftsartikel (refereegranskat)abstract
- The Portable Ice Nucleation Chamber 2 (PINCii) is a newly developed continuous flow diffusion chamber (CFDC) for measuring ice nucleating particles (INPs). PINCii is a vertically oriented parallel-plate CFDC that has been engineered to improve upon the limitations of previous generations of CFDCs. This work presents a detailed description of the PINCii instrument and the upgrades that make it unique compared with other operational CFDCs. The PINCii design offers several possibilities for improved INP measurements. Notably, a specific icing procedure results in low background particle counts, which demonstrates the potential for PINCii to measure INPs at low concentrations ( < 10 L (-1)). High-spatial-resolution wall-temperature mapping enables the identification of temperature inhomogeneities on the chamber walls. This feature is used to introduce and discuss a new method for analyzing CFDC data based on the most extreme lamina conditions present within the chamber, which represent conditions most likely to trigger ice nucleation. A temperature gradient can be maintained throughout the evaporation section in addition to the main chamber, which enables PINCii to be used to study droplet activation processes or to extend ice crystal growth. A series of both liquid droplet activation and ice nucleation experiments were conducted at temperature and saturation conditions that span the spectrum of PINCii's operational conditions ( 50 <= temperature <= 15 degrees C and 100 <= relative humidity with respect to ice <= 160 %) to demonstrate the instrument's capabilities. In addition, typical sources of uncertainty in CFDCs, including particle background, particle loss, and variations in aerosol lamina temperature and relative humidity, are quantified and discussed for PINCii.
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| 8. |
- Johansson, Sofia M., 1983, et al.
(författare)
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Understanding water interactions with organic surfaces: environmental molecular beam and molecular dynamics studies of the water-butanol system
- 2019
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:3, s. 1141-1151
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between water molecules and condensed n-butanol surfaces are investigated at temperatures from 160 to 240 K using the environmental molecular beam experimental method and complementary molecular dynamics (MD) simulations. In the experiments hyperthermal water molecules are directed onto a condensed n-butanol layer and the flux from the surface is detected in different directions. A small fraction of the water molecules scatters inelastically from the surface while losing 60-90% of their initial kinetic energy in collisions, and the angular distributions of these molecules are broad for both solid and liquid surfaces. The majority of the impinging water molecules are thermalized and trapped on the surface, while subsequent desorption is governed by two different processes: one where molecules bind briefly to the surface (residence time < 10 s), and another where the molecules trap for a longer time = 0.8-2.0 ms before desorbing. Water molecules trapped on a liquid n-butanol surface are substantially less likely to escape from the surface compared to a solid layer. The MD calculations provide detialed insight into surface melting, adsorption, absorption and desorption processes. Calculated angular distributions and kinetic energy of emitted water molecules agree well with the experimental data. In spite of its hydrophobic tail and enhanced surface organization below the melting temperature, butanol's hydrophilic functional groups are concluded to be surprisingly accessible to adsorbed water molecules; a finding that may be explained by rapid diffusion of water away from hydrophobic surface structures towards more strongly bound conformational structures.
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| 9. |
- Romero Lejonthun, Liza, 1973, et al.
(författare)
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Chlorine interactions with water ice studied by molecular beam techniques.
- 2006
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Ingår i: The journal of physical chemistry. B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:46, s. 23497-501
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of chlorine interactions with ice at temperatures between 103 and 165 K have been studied using molecular beam techniques. The Cl(2) trapping probability is found to be unity at thermal incident energies, and trapping is followed by rapid desorption. The residence time on the surface is less than 25 microg at temperatures above 135 K and approaches 1 s around 100 K. Rate constants for desorption are determined for temperatures below 135 K. The desorption kinetics follow the Arrhenius equation, and activation energies of 0.24 +/- 0.03 and 0.31 +/- 0.01 eV, with corresponding preexponential factors of 10(12.08+/-1.19) and 10(16.52+/-0.38) s(-1), are determined. At least two different Cl(2) binding sites are concluded to exist on the ice surface. The observed activation energies are likely to be the Cl(2)-ice binding energies for these states, and the Cl(2)-surface interactions are concluded to be stronger than earlier theoretical estimates. The surface coverage of Cl(2) on ice under stratospheric conditions is estimated to be negligible, in agreement with earlier work.
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| 10. |
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| 11. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of ammonia clusters studied by storage ring experiments
- 2006
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 125:19, s. 194306-
-
Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination of ammonia cluster ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for dissociative recombination of H+(NH3)(2), H+(NH3)(3), D+(ND3)(2), and D+(ND3)(3) in the collision energy range of 0.001-27 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 1000 K are calculated from the experimental data and compared with earlier results. The fragmentation patterns for the two ions H+(NH3)(2) and D+(ND3)(2) show no clear isotope effect. Dissociative recombination of X+(NX3)(2) (X=H or D) is dominated by the product channels 2NX(3)+X [0.95 +/- 0.02 for H+(NH3)(2) and 1.00 +/- 0.02 for D+(ND3)(2)]. Dissociative recombination of D+(ND3)(3) is dominated by the channels yielding three N-containing fragments (0.95 +/- 0.05).
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| 12. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of H+(H2O)3 and D+(D2O)3 water cluster ions with electrons: Cross sections and branching ratios
- 2007
-
Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127, s. 194301-194309
-
Tidskriftsartikel (refereegranskat)abstract
- Dissociative recombination (DR) of the water cluster ions H+(H2O)3 and D+(D2O)3 with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H+(H2O)3 in the energy range of 0.001–0.8 eV, and relative cross sections have been measured for D+(D2O)3 in the energy range of 0.001–1.0 eV. The DR cross sections for H+(H2O)3 are larger than previously observed for H+(H2O)n (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H+(H2O)3 mainly results in the formation of 3H2O+H (probability of 0.95±0.05) and with a possible minor channel resulting in 2H2O+OH+H2 (0.05±0.05). The dominating channels for DR of D+(D2O)3 are 3D2O+D (0.88±0.03) and 2D2O+OD+D2 (0.09±0.02). The branching ratios are comparable to earlier DR results for H+(H2O)2 and D+(D2O)2, which gave 2X2O+X (X=H,D) with a probability of over 0.9.
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| 13. |
- Öjekull, Jenny, 1973, et al.
(författare)
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Dissociative recombination of NH4+ and ND4+ ions : Storage ring experiments and ab initio molecular dynamics
- 2004
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:16, s. 7391-7399
-
Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.
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| 14. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Formation of Highly Rovibrationally Excited Ammonia from Dissociative Recombination of NH4
- 2010
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:17, s. 2519-2523
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Tidskriftsartikel (refereegranskat)abstract
- The internal energy distribution of ammonia formed in the dissociative recombination (DR) of NH4+ with electrons has been studied by an imaging technique at the ion storage ring CRYRING. The DR process resulted in the formation of NH3 + H (0.90 ± 0.01), with minor contributions from channels producing NH2 + H2 (0.05 ± 0.01) and NH2 + 2H (0.04 ± 0.02). The formed NH3 molecules were highly internally excited, with a mean rovibrational energy of 3.3 ± 0.4 eV, which corresponds to 70% of the energy released in the neutralization process. The internal energy distribution was semiquantitatively reproduced by ab initio direct dynamics simulations, and the calculations suggested that the NH3 molecules are highly vibrationally excited while rotational excitation is limited. The high internal excitation and the translational energy of NH3 and H will influence their subsequent reactivity, an aspect that should be taken into account when developing detailed models of the interstellar medium and ammonia-containing plasmas.
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| 15. |
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| 16. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Water Condensation on Graphite Studied by Elastic Helium Scattering and Molecular Dynamics Simulations
- 2007
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15258-15266
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Tidskriftsartikel (refereegranskat)abstract
- Formation of water/ice layers on graphite has been studied in the temperature range from 90 to 180 K by elastic helium scattering, light scattering, and molecular dynamics simulations. Combined helium- and light-scattering experiments show that an ice film that wets the graphite surface is formed at surface temperatures of 100-140 K, whereas three-dimensional ice structures are formed at 140-180 K. Desorption of adsorbed water molecules competes with water incorporation into the ice film, and the ice formation rate is strongly temperature dependent. At 150 K, ice-layer formation takes place at the same time scale as layer reconstruction, and its properties are sensitive to the water deposition rate. The experimental results are compared with kinetics models, and the Johnston-Mehl-Avrami-Kolmogorov model is concluded to well describe the ice-layer formation kinetics in the whole temperature range. Molecular dynamics simulations of water-cluster formation on graphite at 90-180 K show that water molecules and small clusters are highly mobile on the surface, which rapidly results in the nucleation of large and less mobile clusters on the surface. Clusters formed at low temperature tend to have the most molecules in direct contact with the uppermost graphite layer, while multilayer cluster structures are preferred at high temperatures. The results are discussed and compared with earlier studies of water ice formation on solid surfaces.
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| 17. |
- Andersson, Viktor, 1994, et al.
(författare)
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A Novel Method for On-Line Characterization of Alkali Release and Thermal Stability of Materials Used in Thermochemical Conversion Processes
- 2022
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 15:12
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metal compounds are released during the thermal conversion of biofuels and fossil fuels and have a major impact on the efficiency of conversion processes. Herein, we describe a novel method for the simultaneous characterization of alkali release and mass loss from materials used in combustion and gasification processes including solid fuels, fluidized bed materials, and catalysts for gas reforming. The method combines the thermogravimetric analysis of selected samples with the on-line measurement of alkali release using a surface ionization detector. The technique builds on the careful treatment of alkali processes during transport from a sample to the downstream alkali monitor including the losses of alkali in the molecular form to hot walls, the formation of nanometer-sized alkali-containing particles during the cooling of exhaust gases, aerosol particle growth, and diffusion losses in sampling tubes. The performance of the setup was demonstrated using biomass samples and fluidized bed material from an industrial process. The emissions of alkali compounds during sample heating and isothermal conditions were determined and related to the simultaneous thermogravimetric analysis. The methodology was concluded to provide new evidence regarding the behavior of alkali in key processes including biomass pyrolysis and gasification and ash interactions with fluidized beds. The implications and further improvements of the technique are discussed.
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| 18. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion
- 2024
-
Ingår i: Fuel. - 0016-2361 .- 1873-7153. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.
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| 19. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali interactions with a calcium manganite oxygen carrier used in chemical looping combustion
- 2022
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 227
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical-Looping Combustion (CLC) of biofuels is a promising technology for cost-efficient CO2 separation and can lead to negative CO2 emissions when combined with carbon capture and storage. A potential challenge in developing CLC technology is the effects of alkali metal-containing compounds released during fuel conversion. This study investigates the interactions between alkali and an oxygen carrier (OC), CaMn0.775Ti0.125Mg0.1O3-δ, to better understand the fate of alkali in CLC. A laboratory-scale fluidized bed reactor is operated at 800–900 °C in oxidizing, reducing and inert atmospheres to mimic CLC conditions. Alkali is fed to the reactor as aerosol KCl particles, and alkali in the exhaust is measured online with a surface ionization detector. The alkali concentration changes with gas environment, temperature, and alkali loading, and the concentration profile has excellent reproducibility over repeated redox cycles. Alkali-OC interactions are dominated by alkali uptake under most conditions, except for a release during OC reduction. Uptake is significant during stable reducing conditions, and is limited under oxidizing conditions. The total uptake during a redox cycle is favored by a high alkali loading, while the influence of temperature is weak. The implications for the understanding of alkali behavior in CLC and further development are discussed.
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| 20. |
- Andersson, Viktor, 1983, et al.
(författare)
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Alkali-wall interactions in a laboratory-scale reactor for chemical looping combustion studies
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metal-containing compounds are readily released during thermal conversion of solid fuels, and may have both detrimental and beneficial effects on chemical looping combustion. Here, we characterize alkali interactions with the inner walls of a laboratory-scale reactor under oxidizing, reducing and inert conditions at temperatures up to 900 °C. KCl aerosol particles are continuously introduced to the stainless steel reactor and the alkali concentration is measured on-line with a surface ionization detector. Aerosol particles evaporate at temperatures above 500 °C and KCl molecules rapidly diffuse to the reactor wall. Up to 92% of the alkali reaching the wall below 700 °C remains adsorbed, while re-evaporation is important at higher temperatures, where up to 74% remains adsorbed. Transient changes in alkali concentration are observed during repeated redox cycles, which are associated with changes in chemical composition of the wall material. Metal oxides on the reactor wall are partially depleted under reducing conditions, which allow for the formation of a new potassium-rich phase that is stable in a reducing atmosphere, but not under inert conditions. The observed wall effects are concluded to be extensive and include major transient effects depending on gas composition, and the implications for laboratory studies and improved experimental methodology are discussed.
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| 21. |
- Andersson, Viktor, 1983, et al.
(författare)
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Design and first application of a novel laboratory reactor for alkali studies in chemical looping applications
- 2023
-
Ingår i: Fuel Processing Technology. - 0378-3820. ; 252
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Tidskriftsartikel (refereegranskat)abstract
- Alkali compounds are readily released during biomass conversion and their complex interactions with reactor walls and sampling equipment makes detailed investigations challenging. This study evaluates a novel laboratory-scale fluidized bed reactor for chemical looping combustion (CLC) studies. The reactor design is based on detailed consideration of the behavior of alkali-containing molecules and aerosol particles and is guided by computational fluid dynamic simulations. The design allows for interactions between gaseous alkali and a fluidized bed, while minimizing alkali interactions with walls before and after the fluidized bed. The function of the laboratory reactor is demonstrated in experiments using online gas and alkali analysis. Alkali is continuously fed to the reactor as KOH or KCl aerosol with and without a fluidized bed of the oxygen carrier CaMn0.775Ti0.125Mg0.1O3-δ present in inert, reducing and oxidizing conditions at temperatures up to 900 °C. Alkali uptake by the OC is characterized in all conditions, and observed to sensitively depend on gas composition, reactor temperature and type of alkali compound. The experimental setup is concluded to have a significantly improved functionality compared to a previously used reactor, which opens up for detailed studies of interactions between alkali compounds and oxygen carriers used in CLC.
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| 22. |
- Andersson, Viktor, 1983, et al.
(författare)
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Gaseous alkali interactions with ilmenite, manganese oxide and calcium manganite under chemical looping combustion conditions
- 2024
-
Ingår i: Fuel Processing Technology. - 0378-3820 .- 1873-7188. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Alkali species present in biomass pose significant challenges in chemical looping combustion (CLC) processes and other thermal conversion applications. The interactions between different alkali species and three common oxygen carrier (OC) materials that are considered to be state of the art in CLC applications have been investigated. A dedicated fluidized bed laboratory reactor was used to study interactions of KCl, NaCl, KOH, NaOH, K2SO4 and Na2SO4 with manganese oxide, calcium manganite and ilmenite. Alkali vapor was generated by injecting alkali salts under reducing, oxidizing and inert conditions at 900 °C. Gaseous species were measured online downstream of the reactor, and the efficiency of alkali uptake was determined under different conditions. The result show significant alkali uptake by all OCs under the studied conditions. Ilmenite shows near complete alkali uptake in reducing conditions, while manganese oxide and calcium manganite exhibited less effective alkali uptake, but have advantages in terms of fuel conversion and oxidizing efficiency. Alkali chlorides, sulfates and hydroxides show distinctly different behavior, with alkali hydroxides being efficiently captured all three investigate OC materials. The findings contribute to a deeper understanding of alkali behavior and offer valuable guidance for the design and optimization of CLC with biomass.
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| 23. |
- Andersson, Viktor, 1994, et al.
(författare)
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Online Speciation of Alkali Compounds by Temperature-Modulated Surface Ionization: Method Development and Application to Thermal Conversion
- 2024
-
Ingår i: ENERGY & FUELS. - 0887-0624 .- 1520-5029. ; 38:3, s. 2046-2057
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for online speciation of potassium- and sodium-containing compounds has been described and demonstrated. The method is based on a temperature-modulated surface ionization (TMSI) technique and may be used to determine the concentrations of alkali chlorides, hydroxides, carbonates, and sulfates in high-temperature processes. The measurement device is a further development of a surface ionization detector (SID) commonly used for online alkali measurements in combustion, gasification, and pyrolysis research. Discrimination between sodium and potassium compounds is made possible by differences in their aerosol evaporation characteristics as a function of temperature combined with the desorption kinetics of alkali on a hot platinum filament. The method is evaluated in laboratory experiments with known alkali salt concentrations. An experimental procedure where the platinum filament in the SID is regularly shifted between three temperatures is concluded to provide sufficient selectivity and time resolution for common applications. The TMSI method is successfully applied to characterize the emission of alkali compounds during pyrolysis of pine wood. The emissions during low-temperature pyrolysis are dominated by KOH, while similar amounts of KOH and NaOH are subsequently emitted from the remaining char and ash. The ability of real-time characterization of individual sodium and potassium compounds opens up new means to understand and optimize solid fuel conversion of common fuels such as low-grade biomass, waste, and coal.
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| 24. |
- Boman, Johan, 1955, et al.
(författare)
-
ASSESSING THE ENVIRONMENT WITH X-RAY FLUORESCENCE
- 2011
-
Ingår i: Advances in X-ray Analysis. - 0376-0308. ; 54, s. 266-279
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we will introduce the general benefits of X-Ray Fluorescence spectrometry (XRF) for assessing the condition of the outer environment, especially where ambient aerosol particles are causing environmental disturbances. Examples from recent environmental studies are presented, and energy dispersive XRF is concluded to be a powerful, nondestructive yet easily applicable tool to supply detailed elemental information of particles collected in different applications. The further development and future potential of the method for detailed analysis of aerosol particles are discussed.
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| 25. |
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| 26. |
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| 27. |
- Bäckström, Daniel, 1985, et al.
(författare)
-
Measurement of the size distribution, volume fraction and optical properties of soot in an 80 kW propane flame
- 2017
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 186, s. 325-334
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents measurements of the size distribution, volume fraction, absorption and scattering coefficients of soot in an 80 kW swirling propane-fired flame. Extractive measurements were performed in the flame using an oil-cooled particle extraction probe. The particle size distribution was measured with a Scanning Mobility Particle Sizer (SMPS) and the optical properties were measured using a Photo Acoustic Soot Spectrometer (PASS-3). A detailed radiation model was used to examine the influence of the soot volume fraction on the particle radiation intensity. The properties of the gas were calculated with a statistical narrow-band model and the particle properties were calculated using Rayleigh theory with four different complex indices of refraction for soot particles. The modelled radiation was compared with measured total radiative intensity, the latter which was measured with a narrow angle radiometer. The results show that the measured soot volume fraction yields particle radiation that corresponds well with the determined difference between gas and total radiation. This indicates that the presented methodology is capable of quantifying both the particle and gaseous radiation in a flame of technical size. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 28. |
- Ding, Saiman, et al.
(författare)
-
Time-resolved alkali release during steam gasification of char in a fixed bed reactor
- 2024
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 356, s. 129528-
-
Tidskriftsartikel (refereegranskat)abstract
- In this study time-resolved char conversion and alkali release under steam gasification conditions were investigated using a fixed bed reactor. The behaviour of an industrial char and chars produced from straw and furniture waste was investigated. For woody chars, an increase in gasification reactivity is observed together with a notable alkali release as the gasification approaches completion (degree of conversion > 0.8). In contrast, straw char exhibited a decrease in conversion rate and alkali release throughout the gasification process, attributed to the formation of catalytically inactive potassium silicates inhibiting the catalytic role of alkali. Aerosol particles in the 0.01–22 µm size range are emitted during the char conversion. A fraction is formed by nucleation of alkali compounds and other condensable gases. A wide particle distribution that extends over the whole size range is also observed, and the particles are likely to consist of solid char fragments. The study concludes on the importance of alkali release, illustrating the difference in alkali release pattern for high and low ash char.
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| 29. |
- Elsasser, M., et al.
(författare)
-
Organic molecular markers and signature from wood combustion particles in winter ambient aerosols: aerosol mass spectrometer (AMS) and high time-resolved GC-MS measurements in Augsburg, Germany
- 2012
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:14, s. 6113-6128
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of wood combustion on ambient aerosols was investigated in Augsburg, Germany during a winter measurement campaign of a six-week period. Special attention was paid to the high time resolution observations of wood combustion with different mass spectrometric methods. Here we present and compare the results from an Aerodyne aerosol mass spectrometer (AMS) and gas chromatographic - mass spectrometric (GC-MS) analysed PM1 filters on an hourly basis. This includes source apportionment of the AMS derived organic matter (OM) using positive matrix factorisation (PMF) and analysis of levoglucosan as wood combustion marker, respectively. During the measurement period nitrate and OM mass are the main contributors to the defined submicron particle mass of AMS and Aethalometer with 28% and 35%, respectively. Wood combustion organic aerosol (WCOA) contributes to OM with 23% on average and 27% in the evening and night time. Conclusively, wood combustion has a strong influence on the organic matter and overall aerosol composition. Levoglucosan accounts for 14% of WCOA mass with a higher percentage in comparison to other studies. The ratio between the mass of levoglucosan and organic carbon amounts to 0.06. This study is unique in that it provides a one-hour time resolution comparison between the wood combustion results of the AMS and the GC-MS analysed filter method at a PM1 particle size range. The comparison of the concentration variation with time of the PMF WCOA factor, levoglucosan estimated by the AMS data and the levoglucosan measured by GC-MS is highly correlated (R-2 = 0.84), and a detailed discussion on the contributors to the wood combustion marker ion at mass-to-charge ratio 60 is given. At the end, both estimations, the WCOA factor and the levoglucosan concentration estimated by AMS data, allow to observe the variation with time of wood combustion emissions (gradient correlation with GC-MS levoglucosan of R-2 = 0.84). In the case of WCOA, it provides the estimated magnitude of wood combustion emission. Quantitative estimation of the levoglucosan concentration from the AMS data is problematic due to its overestimation in comparison to the levoglucosan measured by the GC-MS.
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| 30. |
- Eriksson, Martin, 1970, et al.
(författare)
-
The SDG Impact Assessment Tool – a free online tool for self-assessments of impacts on Agenda 2030
- 2019
-
Ingår i: Proceedings from International Conference on Sustaianable Development.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents the SDG Impact Assessment Tool, an online resource for self- assessments of impacts on the Sustainable Development Goals (SDGs). In addition, it presents a brief example of an SDG Impact Assessment and some existing and potential applications of the tool. The United Nations (UN) 2030 Agenda and the SDGs are a resolution for attaining sustainable development throughout the world, but also represent a framework towards which the sustainability of almost any activity can be evaluated. Although quantitative methods are indeed pivotal for achieving sustainable development, they are often limited to specific scientific fields and cannot encompass all aspects of all SDGs, including normative societal values. A qualitative and reflective approach, however, is not reserved for scientists in specific fields but can be used by anyone. Using such an approach in the tool presented here represent a good starting point for companies or other organizations that want to learn about the SDGs and minimize their negative impacts. The tool employs a self-assessment of impacts on each of the 17 SDGs, in terms of Direct positive, Indirect positive, No impact, Indirect negative, Direct negative or More knowledge needed, and outputs a graphical visualization of the results. The tool also encourages users to formulate a strategy on how to mitigate negative impacts, increase positive impacts and fill potential knowledge gaps, which can be a starting point for a more comprehensive sustainability strategy for companies or other organizations.
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| 31. |
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| 32. |
- Gaita, Samuel Mwaniki, 1976, et al.
(författare)
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Source apportionment and seasonal variation of PM2.5 in a Sub-Sahara African city : Nairobi, Kenya
- 2014
-
Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 14:18, s. 9977-9991
-
Tidskriftsartikel (refereegranskat)abstract
- Sources of airborne particulate matter and their seasonal variation in urban areas in Sub-Saharan Africa are poorly understood due to lack of long-term measurement data. In view of this, filter samples of airborne particulate matter (particle diameter ≤2.5 μm, PM2.5) were collected between May 2008 and April 2010 at two sites (urban background site and suburban site) within the Nairobi metropolitan area. A total of 780 samples were collected and analyzed for particulate mass, black carbon (BC) and 13 trace elements.The average PM2.5 concentration at the urban background site was 21±9.5 μg m−3, whereas the concentration at the suburban site was 13±7.3 μg m−3. The daily PM2.5 concentrations exceeded 25 μg m−3 (the World Health Organization 24 h guideline value) on 29% of the days at the urban background site and 7% of the days at the suburban site. At both sites, BC, Fe, S and Cl accounted for approximately 80% of all detected elements. Positive matrix factorization analysis identified five source factors that contribute to PM2.5 in Nairobi, namely traffic, mineral dust, industry, combustion and a mixed factor (composed of biomass burning, secondary aerosol and aged sea salt).Mineral dust and traffic factors were related to approximately 74% of PM2.5. The identified source factors exhibited seasonal variation, apart from the traffic factor, which was prominently consistent throughout the sampling period. Weekly variations were observed in all factors, with weekdays having higher concentrations than weekends. The results provide information that can be exploited for policy formulation and mitigation strategies to control air pollution in Sub-Saharan African cities.
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| 33. |
- Gall, Dan, et al.
(författare)
-
A new technique for real-time measurements of potassium and sodium aerosols based on field-reversal surface ionization
- 2021
-
Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 32:7
-
Tidskriftsartikel (refereegranskat)abstract
- A new method for real-time measurements of potassium and sodium containing aerosol particles is described and verified. The method is based on surface ionization technique and may be used to explore the alkali chemistry related to high temperature chemistry processes. The measurement device is a further development of the simple and cost-effective surface ionization detector previously used for online alkali measurements in combustion and gasification research. The discrimination between sodium and potassium is possible due to differences in their surface desorption kinetics and facilitated by rapidly reversing the field potential between the ion source and the nearby collector. The instrument is evaluated in a series of laboratory experiments using size-selected alkali salt particles containing KCl, NaCl, K2SO4, Na2SO4, KNO3 and NaNO3. The filament temperature was found to be a key influencing factor in order to optimize the strength and Na-K deviation of the observed ion current. The ability to simultaneously report absolute concentrations of Na and K makes the instrument attractive for solid fuel conversion of alkali-rich fuels such as low-grade biomass and to explore behavior deviations of Na and K in high temperature processes. © 2021 The Author(s). Published by IOP Publishing Ltd.
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| 34. |
- Gall, Dan, et al.
(författare)
-
Online Measurements of Alkali and Heavy Tar Components in Biomass Gasification
- 2017
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 31:8, s. 8152-8161
-
Tidskriftsartikel (refereegranskat)abstract
- Tar and alkali metal compounds are released during biomass gasification and have a major impact on the operation and performance of gasification processes. Herein we describe a novel method for characterization of alkali and heavy tar compounds in the hot product gas formed during gasification. Gas is continuously extracted, cooled and diluted, which results in condensation of tar and alkali into aerosol particles. The thermal stability of these particles is subsequently evaluated using a volatility tandem differential mobility analyzer (VTDMA) method. The technique is adopted from aerosol science where it is frequently used to characterize the thermal properties of aerosol particles. Laboratory studies show that pure and mixed alkali salts and organic compounds evaporate in well-defined temperature ranges, which can be used to determine the chemical composition of particles. The performance of the VTDMA is demonstrated at a 4 MWth dual fluidized bed gasifier using two different types of online sampling systems. Alkali metal compounds and a wide distribution of heavy tar components with boiling points above 400°C are observed in the product gas. Implications and potential further improvements of the technique are discussed.
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| 35. |
- Gall, Dan, et al.
(författare)
-
Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant
- 2018
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 32:1, s. 532-541
-
Tidskriftsartikel (refereegranskat)abstract
- Alkali metal compounds may have positive influences on biomass gasification by affecting char reactivity and tar reforming but may also disturb the process by formation of deposits and agglomerates. We herein present results from online measurements of alkali compounds and particle concentrations in a dual fluidized bed gasifier with an input of 32 MWth. A surface ionization detector was used to measure alkali concentrations in the product gas, and aerosol particle measurement techniques were employed to study concentrations and properties of condensable components in the gas. Measurements were performed during start-up and steady-state operation of the gasifier. The alkali concentration increased to approximately 200 mg m-3 when fuel was fed to the gasifier and continued to rise during activation of the olivine bed by addition of potassium carbonate, while the alkali concentration was in the range from 20 to 60 mg m-3 during steady-state operation. Addition of fresh bed material and recirculated ash had noticeable effects on the observed alkali concentrations, and K2CO3 additions to improve tar chemistry resulted in increased levels of alkali in the product gas. Addition of elemental sulfur led to reduced concentrations of CH4 and heavy tars, while no clear influence on the alkali concentration was observed. The study shows that alkali concentrations are high in the product gas, which has implications for the fluidized bed process, tar chemistry, and operation of downstream components including coolers, filters, and catalytically active materials used for product gas reforming.
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| 36. |
- Gatari, Michael J, et al.
(författare)
-
Inorganic and black carbon aerosol concentrations at a high altitude on Mt Kenya
- 2009
-
Ingår i: X-Ray Spectrometry. - : Wiley. - 0049-8246 .- 1097-4539. ; 38:1, s. 26-36
-
Tidskriftsartikel (refereegranskat)abstract
- Aerosol samples were collected at an altitude of 3678 m on Mt Kenya in August 2001. A virtual impactor was used to collect particles in fine (aerodynamic diameter, da < 2.5 µm) and coarse (2.5 µm < da < 10 µm) size fractions. The samples were analyzed for particulate mass (PM), black carbon (BC) and 15 elements. The PM concentrations varied in the ranges 3.3 ± 1.1-7.8 ± 2.5 µg m-3 (in fine fraction) and 3.7 ± 1.2-9.6 ± 3.0 µg m-3 (in coarse fraction). The fine fraction was dominated by high concentrations of BC, S and K due to particles formed during biomass burning and sulfate particles from secondary processes in the atmosphere. The coarse fraction was dominated by high concentrations of Si, S, Cl, K, Ca and Fe indicative of the presence of soil dust particles. This was further verified by enrichment factors (EFs) calculated using the elemental content of the average crustal rock. Chemical mass balance (CMB) calculations indicated that the PM was largely attributable to biomass burning, mineral dust and sulfate, while contributions from anthropogenic sources were small. Source apportionment of elemental concentrations compared well with that of an earlier study on the southwestern slope of Mt Kenya, while PM and sulfate concentrations were comparable with those observed at high-altitude sites in North America and Europe. The observed concentrations were 5-50 times lower than those of urban Kenya.
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| 37. |
- Ge, Yaxin, 1992, et al.
(författare)
-
Effect of fresh bed materials on alkali release and thermogravimetric behavior during straw gasification
- 2023
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 336
-
Tidskriftsartikel (refereegranskat)abstract
- Alkali-associated problems are key issues for the efficient use of straw that is available as a major renewable energy resource worldwide. The effects of six bed materials commonly used in fluidized bed reactors on straw pyrolysis and char gasification were evaluated using online monitoring of alkali release and thermogravimetric analysis. Scanning electron microscopy with energy dispersive spectroscopy was used to determine the elemental composition of the char surface. In the straw pyrolysis stage, alkali release is reduced by the addition of dolomite and silica due to alkali adsorption on the bed materials, and enhanced by the addition of alumina because of its high sodium content. In the char gasification stage, silica, sea sand, olivine, and ilmenite reduce the char reactivity and alkali release, which is attributed to transfer of Si and Ti from the bed materials to the char and reaction with alkali to form stable and catalytically inactive compounds. Alumina also reduces the char conversion rate by transfer of Al to the char and formation of K-Al-Si and Ca-Al-Si compounds, while alkali release from the straw and alumina blend remains high due to the high Na content in alumina. Dolomite initially appears to increase the char gasification reactivity, but the results are affected by conversion of volatile matter that deposited on the dolomite in the straw pyrolysis stage. Dolomite also significantly increases the alkali release, which is attributed to Ca reactions with aluminosilicate compounds that allow potassium to remain in volatile form. Fresh bed materials are concluded to have significant effects on straw conversion depending on their chemical composition, and the results can contribute to the understanding required for efficient use of straw in commercial applications of biomass thermochemical conversion.
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| 38. |
- Ge, Yaxin, et al.
(författare)
-
Effects of used bed materials on char gasification : Investigating the role of element migration using online alkali measurements
- 2022
-
Ingår i: Fuel processing technology. - : Elsevier. - 0378-3820 .- 1873-7188. ; 238
-
Tidskriftsartikel (refereegranskat)abstract
- Online alkali measurements using surface ionization are employed to study alkali release during heating of used industrial fluidized bed materials and gasification of biomass-based char and bed material mixtures. The alkali release from the bed materials starts at 820 °C and increases with temperature, the time a bed material has experienced in an industrial process, and in the presence of CO2. Online alkali measurement during heating of char mixed with used bed material shows significant alkali uptake by the char. Complementary SEM-EDS studies confirm the alkali results and indicate that other important inorganic elements including Si, Mg, and Ca also migrate from the bed material to the char. The migration of elements initially enhances alkali release and char reactivity, but significantly reduces both during the final stage of the gasification. The observed effects on char gasification become more pronounced with increasing amount of bed material and increasing time the material experienced in an industrial process. The ash-layer on the used bed material is concluded to play an important role as a carrier of alkali and other active components. The char and bed material systems are closely connected under operational conditions, and their material exchange has important implications for the thermal conversion.
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| 39. |
- Ge, Yaxin, 1992, et al.
(författare)
-
Impacts of fresh bed materials on alkali release and fuel conversion rate during wood pyrolysis and char gasification
- 2023
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 353
-
Tidskriftsartikel (refereegranskat)abstract
- Bed materials provide efficient heat transfer and catalytic function in the thermochemical conversion of biomass, but their interactions with the fuel remain incompletely understood. In this study, the effects of bed materials on alkali release and fuel conversion during wood pyrolysis and CO2 gasification are investigated by online alkali detection combined with thermogravimetric analysis. The investigated bed materials include silica, sea sand, alumina and the natural ores olivine, ilmenite and dolomite. Only dolomite has a significant effect on fuel mass loss and alkali release during wood pyrolysis, while all bed materials influence char reactivity and alkali release during gasification. Sea sand, alumina and dolomite enhance the char gasification during the whole or most of the gasification process, which is related to alkali migration from the bed materials. All bed materials affect char reactivity and alkali release when the conversion approaches completion, and small amounts of some bed materials reduce the alkali release by an order of magnitude. The findings can be understood based on the chemical composition of the different materials. Silicon-rich materials reduce the levels of catalytically active alkali by formation of stable alkali silicates, and a similar explanation applies for ilmenite that captures alkali efficiently. Magnesium and calcium in contrast promote alkali release through their influence on alkali silicate chemistry. Analysis of char surfaces using scanning electron microscopy with energy dispersive spectroscopy indicates that low amounts of several elements are transferred from the bed material to the char where they may be directly involved in the char conversion process. The transferred elements are specific for each bed material and relates to their chemical composition. Mechanisms for material exchange between bed material and char are discussed.
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| 40. |
- Ge, Yaxin, 1992, et al.
(författare)
-
Online monitoring of alkali release during co-pyrolysis/gasification of forest and agricultural waste: Element migration and synergistic effects
- 2023
-
Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534 .- 1873-2909. ; 172, s. 106745-106745
-
Tidskriftsartikel (refereegranskat)abstract
- Fuel blends may be used to meet several operational needs in thermal conversion of biomass waste, including optimization of ash properties and fuel conversion efficiency. In this study, online alkali measurements using surface ionization are employed to study synergistic effects produced by inorganic elements during co-pyrolysis/gasification of wood and straw waste. Synergistic effects on the fuel conversion behavior are not observed during co-pyrolysis, while alkali migration from straw to wood is clearly observed above 600 °C by online alkali monitoring. In contrast, synergistic effects on char conversion and alkali release are substantial during co-gasification. Positive effects on char reactivity during most of the gasification process are attributed to alkali migration from the straw to the wood char, and the most pronounced effect occurs at a gasification temperature of 900 °C and a straw content of 25%. Negative effects on char reactivity are observed at the final gasification stage, which is associated with a significantly reduced alkali release from fuel blends compared to pure wood char. The effect is attributed to the migration of silicon, phosphorus, and aluminum to the wood char, as revealed by scanning electron microscopy with energy dispersive spectroscopy, where the elements react with alkali to form catalytically inactive compounds. The mixing of biofuels is concluded to result in substantial effects on the fuel conversion efficiency, which should be taken into consideration in thermochemical conversion of biomass.
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| 41. |
- Ge, Yaxin, 1992, et al.
(författare)
-
Real-time monitoring of alkali release during CO2 gasification of different types of biochar
- 2022
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 327
-
Tidskriftsartikel (refereegranskat)abstract
- Potassium and sodium compounds play both positive and negative roles during biomass gasification, but the detailed behavior of alkali metal compounds remain incompletely understood. In this study, alkali release during CO2 gasification of biochar is characterized online with a surface ionization method in combination with thermogravimetric analysis of the char samples undergoing gasification. For wood chars, the alkali release rate follows a slowly decreasing trend as the char conversion proceeds, but increases by up to two orders of magnitude when the conversion approaches completion. In contrast, the alkali release from straw char is 40-50 times higher than observed for wood char and decreases continuously during the whole gasification process. A high temperature and a high CO2 concentration enhance both alkali release and char reactivity. The char preparation method also influences the alkali release from pine char, while the char reactivity is less affected. Alkali release and char reactivity are linked, but other factors including mineral content, surface area and char structure may play important roles for the observed reactivity. The results provide a basis for understanding of alkali behavior during gasification and may help optimize catalytic effects and reduce detrimental issues in biomass gasification.
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| 42. |
- Gogolev, Ivan, 1984, et al.
(författare)
-
Chemical-looping combustion in a 100 kW unit using a mixture of synthetic and natural oxygen carriers - Operational results and fate of biomass fuel alkali
- 2019
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 88, s. 371-382
-
Tidskriftsartikel (refereegranskat)abstract
- Biomass fuel use in chemical looping combustion enables negative CO2 emissions through BECCS (Bio-Energy Carbon Capture and Storage). Effective biomass utilization in CLC requires an economical and effective oxygen carrier to achieve high fuel conversion, effective CO2 capture, and management of the harmful effects of biomass alkali release (bed agglomeration, oxygen carrier deactivation, fouling and corrosion). These issues were addressed in 100 kW CLC pilot experiments. Building on previous work, a mixture of a synthetic calcium manganite perovskite and natural ilmenite was used as the oxygen carrier. Four biomass fuels of varied alkali content were tested: black pellets of steam-exploded stem wood (BP), BP impregnated with K2CO3, a mixture of 50% BP with 50% straw pellets, and wood char. Experiments showed high fuel conversion and very high CO2 capture, with overall performance exceeding that of ilmenite and manganese ore. More than 95% gas conversion was achieved with black pellets at around 950 degrees C. The fate of biomass alkali, previously virtually unknown in CLC research, was explored by implementing online surface-ionization-based measurement of alkali released in the flue gases of the fuel reactor (FR) and air reactor (AR). Release levels were found to correlate with the fuel alkali content. The flue gas measurements and bed material elemental analyses suggest that most of the fuel alkali are accumulated in the oxygen carrier. Unexpectedly, it was found that flue gas alkali release occurs in both the FR and AR, with AR exhibiting an equal or higher rate of release vs. the FR.
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| 43. |
- Grawe, S., et al.
(författare)
-
The immersion freezing behavior of ash particles from wood and brown coal burning
- 2016
-
Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:21, s. 13911-13928
-
Tidskriftsartikel (refereegranskat)abstract
- It is generally known that ash particles from coal combustion can trigger ice nucleation when they interact with water vapor and/or supercooled droplets. However, data on the ice nucleation of ash particles from different sources, including both anthropogenic and natural combustion processes, are still scarce. As fossil energy sources still fuel the largest proportion of electric power production worldwide, and biomass burning contributes significantly to the global aerosol loading, further data are needed to better assess the ice nucleating efficiency of ash particles. In the framework of this study, we found that ash particles from brown coal (i.e., lignite) burning are up to 2 orders of magnitude more ice active in the immersion mode below -32 degrees C than those from wood burning. Fly ash from a coal-fired power plant was shown to be the most efficient at nucleating ice. Furthermore, the influence of various particle generation methods on the freezing behavior was studied. For instance, particles were generated either by dispersion of dry sample material, or by atomization of ash-water suspensions, and then led into the Leipzig Aerosol Cloud Interaction Simulator (LACIS) where the immersion freezing behavior was examined. Whereas the immersion freezing behavior of ashes from wood burning was not affected by the particle generation method, it depended on the type of particle generation for ash from brown coal. It was also found that the common practice of treating prepared suspensions in an ultrasonic bath to avoid aggregation of particles led to an enhanced ice nucleation activity. The findings of this study suggest (a) that ash from brown coal burning may influence immersion freezing in clouds close to the source and (b) that the freezing behavior of ash particles may be altered by a change in sample preparation and/or particle generation.
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| 44. |
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| 45. |
- Hak, Claudia S., 1976, et al.
(författare)
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A new approach to in-situ determination of roadside particle emission factors of individual vehicles under conventional driving conditions
- 2009
-
Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 43:15, s. 2481-2488
-
Tidskriftsartikel (refereegranskat)abstract
- A method for continuous on-road measurements of particle number emissions for both diesel- and petrol-fuelled vehicles is presented. The setup allows the determination of particle number emission factors on an individual vehicle basis by the simultaneous measurement of CO2 and particle concentrations. As an alternative to previous measurements on the kerbside, the sample is taken directly in the street, with the advantage of sampling in-situ within the exhaust plumes of passing vehicles, allowing the separation of the individual high-concentration plumes. The method was tested in two experiments that were conducted in the Gothenburg area. In the first study, which was performed at an urban roadside, we were able to determine particle emission factors from individual vehicles in a common car fleet passing the measurement site. The obtained emission factors were of the same order of magnitude (between 1.4 × 1012 and 1.8 × 1014 particles km−1) as values published in the recent literature for light duty vehicles. An additional on-road experiment was conducted at a rural road with four light duty reference vehicles (three of them petrol-powered and one diesel-powered) at driving speeds of 50 and 70 km h−1, realised with different engine speeds. The results of the traffic emission studies show that the method is applicable provided that instruments with an adequate dynamic range are used and that the traffic is not too dense. In addition, the variability in particle emissions for a specified driving condition was estimated.
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| 46. |
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| 47. |
- Hallquist, Mattias, 1969, et al.
(författare)
-
Photochemical smog in China: scientific challenges and implications for air-quality policies
- 2016
-
Ingår i: National Science Review. - : Oxford University Press (OUP). - 2095-5138 .- 2053-714X. ; 3:4, s. 401-403
-
Tidskriftsartikel (refereegranskat)abstract
- In large areas of China severe air pollution events pose a significant threat to human health, ecosystems and climate. Current reduction of primary emissions will also affect secondary pollutants such as ozone (O3) and particulate matter (PM), but the magnitude of the effects is uncertain. Major scientific challenges are related to the formation of O3 and secondary particulate matter including Secondary Organic Aerosols (SOA). Large uncertainties also remain regarding the interactions of soot, SOA and O3 under the influence of different SO2, NOX and VOC concentrations. To improve the understanding of these secondary atmospheric interactions in China, scientific areas of central importance for photochemically induced air pollutants have been identified. In addition to the scientific challenges, results from research need to be synthesized across several disciplines and communicated to stakeholders affected by air pollution and to policy makers responsible for developing abatement strategies. Development of these science-policy interactions can benefit from experience gained under the UN ECE Convention on Long Range Transboundary Air Pollution (LRTAP)
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| 48. |
- Janhäll, Sara, 1965, et al.
(författare)
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Evolution of the urban aerosol during winter temperature inversion episodes
- 2006
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 40:28, s. 5355-5366
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Tidskriftsartikel (refereegranskat)abstract
- Winter temperature inversions are for Nordic urban sites a major cause for exceeding air-quality legislation thresholds for most primary pollutants. In this study, number particle size distributions have been measured and compared to other tracers for traffic emissions. Concentrations during winter days with and without morning temperature inversion were compared. Morning temperature inversion resulted in high concentrations of traffic-related pollutants, including CO, NO and NO2 together with ultrafine particles, while the pollution levels where considerably lower during mornings without temperature inversion. The specific time trends of NOx species could be well understood when considering the reaction with O-3. The two different particle measures used in this study, i.e. the number concentration of ultrafine particles (10-100 nm) and the mass of particles below 10 pm (PM10), both increased during morning rush hours. When the morning inversion broke up and ground-level air mixed with air aloft, the number of particles decreased more rapidly than PM10 concentrations. LIDAR measurements were used to follow the vertical distribution of particles, and they clearly showed how the mixing processes started after the morning inversion and resulted in rising of the inversion followed by a relatively well-mixed boundary layer with a height of I kin around 14:00. (c) 2006 Elsevier Ltd. All rights reserved.
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| 49. |
- Johansson, Sofia M., 1983, et al.
(författare)
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A novel gas-vacuum interface for environmental molecular beam studies
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:3
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Tidskriftsartikel (refereegranskat)abstract
- Molecular beam techniques are commonly used to obtain detailed information about reaction dynamics and kinetics of gas-surface interactions. These experiments are traditionally performed in vacuum and the dynamic state of surfaces under ambient conditions is thereby excluded from detailed studies. Herein we describe the development and demonstration of a new vacuum-gas interface that increases the accessible pressure range in environmental molecular beam (EMB) experiments. The interface consists of a grating close to a macroscopically flat surface, which allows for experiments at pressures above 1 Pa including angularly resolved measurements of the emitted flux. The technique is successfully demonstrated using key molecular beam experiments including elastic helium and inelastic water scattering from graphite, helium and light scattering from condensed adlayers, and water interactions with a liquid 1-butanol surface. The method is concluded to extend the pressure range and flexibility in EMB studies with implications for investigations of high pressure interface phenomena in diverse fields including catalysis, nanotechnology, environmental science, and life science. Potential further improvements of the technique are discussed. Published by AIP Publishing.
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| 50. |
- Johansson, Sofia M., 1983, et al.
(författare)
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Experimental and Computational Study of Molecular Water Interactions with Condensed Nopinone Surfaces Under Atmospherically Relevant Conditions
- 2020
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 124:18, s. 3652-3661
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Tidskriftsartikel (refereegranskat)abstract
- Water and organics are omnipresent in the atmosphere, and their interactions influence the properties and lifetime of both aerosols and clouds. Nopinone is one of the major reaction products formed from beta-pinene oxidation, a compound emitted by coniferous trees, and it has been found in both gas and particle phases in the atmosphere. Here, we investigate the interactions between water molecules and nopinone surfaces by combining environmental molecular beam (EMB) experiments and molecular dynamics (MD) simulations. The EMB method enables detailed studies of the dynamics and kinetics of water interacting with solid nopinone at 170-240 K and graphite coated with a molecularly thin nopinone layer at 200-270 K. MD simulations that mimic the experimental conditions have been performed to add insights into the molecular-level processes. Water molecules impinging on nopinone surfaces are efficiently trapped (>= 97%), and only a minor fraction scatters inelastically while maintaining 35-65% of their incident kinetic energy (23.2 +/- 1.0 kJ mol(-1)). A large fraction (60-80%) of the trapped molecules desorbs rapidly, whereas a small fraction (20-40%) remains on the surface for more than 10 ms. The MD calculations confirm both rapid water desorption and the occurrence of strongly bound surface states. A comparison of the experimental and computational results suggests that the formation of surface-bound water clusters enhances water uptake on the investigated surfaces.
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