| 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. |
- 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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| 4. |
- Bäckström, Daniel, 1985, et al.
(författare)
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Measurement of the size distribution, volume fraction and optical properties of soot in an 80 kW propane flame
- 2017
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 186, s. 325-334
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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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| 5. |
- Eriksson, Martin, 1970, et al.
(författare)
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The SDG Impact Assessment Tool – a free online tool for self-assessments of impacts on Agenda 2030
- 2019
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Ingår i: Proceedings from International Conference on Sustaianable Development.
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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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| 6. |
- Gall, Dan, et al.
(författare)
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Online Measurements of Alkali and Heavy Tar Components in Biomass Gasification
- 2017
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 31:8, s. 8152-8161
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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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| 7. |
- Gall, Dan, et al.
(författare)
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Online Measurements of Alkali Metals during Start-up and Operation of an Industrial-Scale Biomass Gasification Plant
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 32:1, s. 532-541
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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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| 8. |
- Gogolev, Ivan, 1984, et al.
(författare)
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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
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 88, s. 371-382
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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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| 9. |
- Grawe, S., et al.
(författare)
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The immersion freezing behavior of ash particles from wood and brown coal burning
- 2016
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:21, s. 13911-13928
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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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| 10. |
- Hallquist, Mattias, 1969, et al.
(författare)
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Photochemical smog in China: scientific challenges and implications for air-quality policies
- 2016
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Ingår i: National Science Review. - : Oxford University Press (OUP). - 2095-5138 .- 2053-714X. ; 3:4, s. 401-403
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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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| 11. |
- 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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| 12. |
- Johansson, Sofia M., 1983, et al.
(författare)
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The Dynamics and Kinetics of Water Interactions with a Condensed Nopinone Surface.
- 2017
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Ingår i: The journal of physical chemistry. A. - : American Chemical Society (ACS). - 1520-5215 .- 1089-5639. ; 121:35, s. 6614-6619
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Tidskriftsartikel (refereegranskat)abstract
- Water and organic molecules are omnipresent in the environment, and their interactions are of central importance in many Earth system processes. Here we investigate molecular-level interactions between water and a nopinone surface using an environmental molecular beam (EMB) technique. Nopinone is a major reaction product formed during oxidation of β-pinene, a prominent compound emitted by coniferous trees, which has been found in both the gas and particle phases of atmospheric aerosol. The EMB method enables detailed studies of the dynamics and kinetics of D2O molecules interacting with a solid nopinone surface at 202 K. Hyperthermal collisions between water and nopinone result in efficient trapping of water molecules, with a small fraction that scatter inelastically after losing 60-80% of their incident kinetic energy. While the majority of the trapped molecules rapidly desorb with a time constant τ less than 10 μs, a substantial fraction (0.32 ± 0.09) form strong bonds with the nopinone surface and remain in the condensed phase for milliseconds or longer. The interactions between water and nopinone are compared to results for recently studied water-alcohol and water-acetic acid systems, which display similar collision dynamics but differ with respect to the kinetics of accommodated water. The results contribute to an emerging surface science-based view and molecular-level description of organic aerosols in the atmosphere.
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| 13. |
- Kong, Xiangrui, et al.
(författare)
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Dynamics and Kinetics of Methanol-Graphite Interactions at Low Surface Coverage
- 2019
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Ingår i: Chemphyschem. - : Wiley. - 1439-4235 .- 1439-7641. ; 20:17, s. 2171-2178
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Tidskriftsartikel (refereegranskat)abstract
- The processes of molecular clustering, condensation, nucleation, and growth of bulk materials on surfaces, represent a spectrum of vapor-surface interactions that are important to a range of physical phenomena. Here, we describe studies of the initial stages of methanol condensation on graphite, which is a simple model system where gas-surface interactions can be described in detail using combined experimental and theoretical methods. Experimental molecular beam methods and computational molecular dynamics simulations are used to investigate collision dynamics and surface accommodation of methanol molecules and clusters at temperatures from 160 K to 240 K. Both single molecules and methanol clusters efficiently trap on graphite, and even in rarified systems methanol-methanol interactions quickly become important. A kinetic model is developed to simulate the observed behavior, including the residence time of trapped molecules and the quantified Arrhenius kinetics. Trapped molecules are concluded to rapidly diffuse on the surface to find and/or form clusters already at surface coverages below 10(-6) monolayers. Conversely, clusters that undergo surface collisions fragment and subsequently lose more loosely bound molecules. Thus, the surface mediates molecular collisions in a manner that minimizes the importance of initial cluster size, but highlights a strong sensitivity to surface diffusion and intermolecular interactions between the hydrogen bonded molecules.
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| 14. |
- Kong, Xiangrui, et al.
(författare)
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Rapid Water Transport through Organic Layers on Ice
- 2018
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 122:21, s. 4861-4868
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Tidskriftsartikel (refereegranskat)abstract
- Processes involving atmospheric aerosol and cloud particles are affected by condensation of organic compounds that are omnipresent in the atmosphere. On ice particles, organic compounds with hydrophilic functional groups form hydrogen-bonds with the ice and orient their hydrophobic groups away from the surface. The organic layer has been expected to constitute a barrier to gas uptake, but recent experimental studies suggest that the accommodation of water molecules on ice is only weakly affected by condensed short-chain alcohol layers. Here, we employ molecular dynamics simulations to study the water interactions with n-butanol covered ice at 200 K, and show that the small effect of the condensed layer is due to efficient diffusion of water molecules along the surface plane while seeking appropriate sites to penetrate, followed by penetration driven by the combined attractive forces from butanol OH groups and water molecules within the ice. The water molecules that penetrate through the n-butanol layer become strongly bonded by approximately three hydrogen bonds at the butanol-ice interface. The obtained accommodation coefficient (0.81 ± 0.03) is in excellent agreement with results from previous environmental molecular beam experiments, leading to a picture where an adsorbed n-butanol layer does not alter the apparent accommodation coefficient, but dramatically changes the detailed molecular dynamics and kinetics.
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| 15. |
- Moud, Pouya H., et al.
(författare)
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Effect of gas phase alkali species on tar reforming catalyst performance : Initial characterization and method development
- 2015
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 154, s. 95-106
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Tidskriftsartikel (refereegranskat)abstract
- In thermochemical conversion of biomass to synthesis gas and biofuels, the effect of varying gas phase alkali concentrations on tar reforming catalyst performance in combination with gas phase sulfur and chlorine is largely unknown. The current study demonstrates a new methodology for investigating gas phase alkali adsorption and presents results for early stage adsorption on a Ni-based catalyst under realistic industrial conditions. The experiments were carried out using pine pellets as feedstock in a setup consisting of a 5 kW atmospheric bubbling fluidized bed gasifier, a high temperature hot gas filter and a catalytic reactor - all operating at 850 °C. A potassium chloride solution was atomized with an aerosol generator, and the produced submicrometer KCl particles were continuously introduced to the catalytic reactor where they rapidly evaporated to form KCl (g). The accurate dosing of gas-phase alkali was combined with elimination of transient effects in catalytic performance due to catalyst sintering and S adsorption, and results for K uptake in relation to sulfur uptake were obtained. Different KCl levels in the gas phase demonstrates different initial uptake of K on the catalyst surface, which at low K coverage (θK) is approximately linearly proportional to time on stream. The results also show a clear suppressing effect of sulfur adsorption on potassium uptake. Indications of a slow approach to K equilibration on the catalyst were observed. The potential of the developed methodology for detailed studies under close to industrial conditions is discussed.
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| 16. |
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| 17. |
- Pettersson, Jan B. C., 1962, et al.
(författare)
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Dissociative recombination and excitation of D-5(+) by collisions with low-energy electrons
- 2015
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Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 113:15-16, s. 2099-2104
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Tidskriftsartikel (refereegranskat)abstract
- We report results from high-resolution studies of D-5(+) cluster ion collisions with low-energy electrons performed in a heavy ion storage ring. Absolute dissociative recombination (DR) and dissociative excitation (DE) cross sections were determined for the energy range from 0.0005 to 20eV. The DR cross sections were exceedingly large at low energies, and DR resulted in efficient internal energy redistribution and pronounced fragmentation with two main product channels: D-2+3D (0.62 +/- 0.03) and 2D(2)+D (0.35 +/- 0.01). The DR and DE cross sections were comparable in the energy range from 0.2 to 20eV, which suggest that the two processes follow similar dynamics and are competing outcomes of the ion-electron interaction. A simple picture of the recombination process of D-5(+) which captures the essential physics is suggested. RAHAMSSON K, 1993, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM
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| 18. |
- Pushp, Mohit, et al.
(författare)
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Influence of Bed Material, Additives, and Operational Conditions on Alkali Metal and Tar Concentrations in Fluidized Bed Gasification of Biomass
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 32:6, s. 6797-6806
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Tidskriftsartikel (refereegranskat)abstract
- Gasification of biomass results in release of tar and alkali metal compounds that constitute a significant challenge to the optimization of the gasification process. Here we describe on-line measurements of alkali, condensable tar, and particle concentrations in product gas from a 2-4 MWth dual fluidized bed gasifier, with the aims to characterize typical concentrations and contribute to the understanding of alkali-tar interactions. The influence of bed material, additives, and operational parameters on the concentrations is investigated. Alkali concentrations are measured with a surface ionization detector, and particle and tar concentrations are determined using aerosol measurement techniques. The gasification of wood chips using quartz or olivine as bed material results in an alkali concentration of 30-250 mg m-3, and the observed alkali levels are consistent with a significant release of the fuel alkali content. Addition of ilmenite to a quartz bed and additions of K2SO4 and K2CO3 to an olivine bed influence both alkali and heavy tar concentrations. The additions result in changes in alkali concentration that relaxes to a new steady state in tens of minutes. The concentration of condensable tar is lower for the olivine bed than for the quartz bed, and tends to decrease when potassium or sulfur is added. The concentration of condensable tar compounds is anticorrelated with the alkali concentration when a quartz bed is used, while no clear trend is observed with an olivine bed. An increase in steam flow rate results in a substantial decrease in heavy tar concentration from a quartz sand bed, while the alkali concentration increases slightly with increasing flow rate. This is in contrast to the alkali concentrations observed when using an activated olivine bed, where concentrations are higher and tend to decrease with increasing steam flow rate. The study confirms that several primary methods are available to optimize the alkali and tar behavior in the gasifier, and suggests that on-line monitoring is needed to systematically change the operational conditions and to study the underlying processes.
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| 19. |
- Tan, Wen, et al.
(författare)
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Theoretical and Experimental Study on the Reaction of tert-Butylamine with OH Radicals in the Atmosphere
- 2018
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 122:18, s. 4470-4480
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 American Chemical Society. The OH-initiated atmospheric degradation of tert-butylamine (tBA), (CH 3 ) 3 CNH 2 , was investigated in a detailed quantum chemistry study and in laboratory experiments at the European Photoreactor (EUPHORE) in Spain. The reaction was found to mainly proceed via hydrogen abstraction from the amino group, which in the presence of nitrogen oxides (NO x ), generates tert-butylnitramine, (CH 3 ) 3 CNHNO 2 , and acetone as the main reaction products. Acetone is formed via the reaction of tert-butylnitrosamine, (CH 3 ) 3 CNHNO, and/or its isomer tert-butylhydroxydiazene, (CH 3 ) 3 CN=NOH, with OH radicals, which yield nitrous oxide (N 2 O) and the (CH 3 ) 3 Ċ radical. The latter is converted to acetone and formaldehyde. Minor predicted and observed reaction products include formaldehyde, 2-methylpropene, acetamide and propan-2-imine. The reaction in the EUPHORE chamber was accompanied by strong particle formation which was induced by an acid-base reaction between photochemically formed nitric acid and the reagent amine. The tert-butylaminium nitrate salt was found to be of low volatility, with a vapor pressure of 5.1 × 10 -6 Pa at 298 K. The rate of reaction between tert-butylamine and OH radicals was measured to be 8.4 (±1.7) × 10 -12 cm 3 molecule -1 s -1 at 305 ± 2 K and 1015 ± 1 hPa.
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| 20. |
- Thomson, Erik S, et al.
(författare)
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Deposition-mode ice nucleation reexamined at temperatures below 200 K
- 2015
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 15:4, s. 1621-1632
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Tidskriftsartikel (refereegranskat)abstract
- The environmental chamber of a molecular beam apparatus is used to study deposition nucleation of ice on graphite, alcohols and acetic and nitric acids at temperatures between 155 and 200 K. The critical supersaturations necessary to spontaneously nucleate water ice on six different substrate materials are observed to occur at higher supersaturations than are theoretically predicted. This contradictory result motivates more careful examination of the experimental conditions and the underlying basis of the current theories. An analysis based on classical nucleation theory supports the view that at these temperatures nucleation is primarily controlled by the rarification of the vapor and the strength of water's interaction with the substrate surface. The technique enables a careful probing of the underlying processes of ice nucleation and the substrate materials of study. The findings are relevant to atmospheric nucleation processes that are intrinsically linked to cold cloud formation and lifetime.
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| 21. |
- Thomson, Erik S, et al.
(författare)
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Intensification of ice nucleation observed in ocean ship emissions
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Shipping contributes primary and secondary emission products to the atmospheric aerosol burden that have implications for climate, clouds, and air quality from regional to global scales. In this study we exam the potential impact of ship emissions with regards to ice nucleating particles. Particles that nucleate ice are known to directly affect precipitation and cloud microphysical properties. We have collected and analyzed particles for their ice nucleating capacity from a shipping channel outside a large Scandinavia port. We observe that ship plumes amplify the background levels of ice nucleating particles and discuss the larger scale implications. The measured ice nucleating particles suggest that the observed amplification is most likely important in regions with low levels of background particles. The Arctic, which as the sea ice pack declines is opening to transit and natural resource exploration and exploitation at an ever increasing rate, is highlighted as such a region.
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