| 21. |
- Zhao, D. F., et al.
(författare)
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Size-dependent hygroscopicity parameter (κ) and chemical composition of secondary organic cloud condensation nuclei
- 2015
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Ingår i: Geophysical Research Letters. - 1944-8007. ; 42:24
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Tidskriftsartikel (refereegranskat)abstract
- Secondary organic aerosol components (SOA) contribute significantly to the activation of cloud condensation nuclei (CCN) in the atmosphere. The CCN activity of internally mixed submicron SOA particles is often parameterized assuming a size-independent single-hygroscopicity parameter κ. In the experiments done in a large atmospheric reactor (SAPHIR, Simulation of Atmospheric PHotochemistry In a large Reaction chamber, Jülich), we consistently observed size-dependent κ and particle composition for SOA from different precursors in the size range of 50nm–200nm. Smaller particles had higher κ and a higher degree of oxidation, although all particles were formed from the same reaction mixture. Since decreasing volatility and increasing hygroscopicity often covary with the degree of oxidation, the size dependence of composition and hence of CCN activity can be understood by enrichment of higher oxygenated, low-volatility hygroscopic compounds in smaller particles. Neglecting the size dependence of κ can lead to significant bias in the prediction of the activated fraction of particles during cloud formation.
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| 22. |
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| 23. |
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| 24. |
- Tsiligiannis, Epameinondas, et al.
(författare)
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Effect of NOx on 1,3,5-trimethylbenzene (TMB) oxidation product distribution and particle formation
- 2019
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:23, s. 15073-15086
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Tidskriftsartikel (refereegranskat)abstract
- Secondary organic aerosol (SOA) represents a significant fraction of the tropospheric aerosol and its precursors are volatile organic compounds (VOCs). Anthropogenic VOCs (AVOC) dominate the VOC budget in many urban areas with 1,3,5-trimethylbenzene (TMB) being among the most reactive aromatic AVOCs. TMB formed highly oxygenated organic molecules (HOMs) in an NOx-free environment, which could contribute to new particle formation (NPF) depending on oxidation conditions where elevated OH oxidation enhanced particle formation. The experiments were performed in an oxidation flow reactor, the Go:PAM unit, under controlled OH oxidation conditions. By addition of NOx to the system we investigated the effect of NOx on particle formation and on the product distribution. We show that the formation of HOMs, and especially HOM accretion products, strongly varies with NOx conditions. We observe a suppression of HOM and particle formation with increasing NOx/ΔTMB ratio and an increase in the formation of organonitrates (ONs) mostly at the expense of HOM accretion products. We propose reaction mechanisms and pathways that explain the formation and observed product distributions with respect to oxidation conditions. We hypothesise that, based on our findings from TMB oxidation studies, aromatic AVOCs may not contribute significantly to NPF under typical NOx/AVOC conditions found in urban atmospheres.
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| 25. |
- Sun, Bing, et al.
(författare)
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Ion transport in polycarbonate based solid polymer electrolytes : experimental and computational investigations
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:14, s. 9504-9513
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Tidskriftsartikel (refereegranskat)abstract
- Among the alternative host materials for solid polymer electrolytes (SPEs), polycarbonates have recently shown promising functionality in all-solid-state lithium batteries from ambient to elevated temperatures. While the computational and experimental investigations of ion conduction in conventional polyethers have been extensive, the ion transport in polycarbonates has been much less studied. The present work investigates the ionic transport behavior in SPEs based on poly(trimethylene carbonate) (PTMC) and its co-polymer with epsilon-caprolactone (CL) via both experimental and computational approaches. FTIR spectra indicated a preferential local coordination between Li+ and ester carbonyl oxygen atoms in the P(TMC20CL80) co-polymer SPE. Diffusion NMR revealed that the co-polymer SPE also displays higher ion mobilities than PTMC. For both systems, locally oriented polymer domains, a few hundred nanometers in size and with limited connections between them, were inferred from the NMR spin relaxation and diffusion data. Potentiostatic polarization experiments revealed notably higher cationic transference numbers in the polycarbonate based SPEs as compared to conventional polyether based SPEs. In addition, MD simulations provided atomic-scale insight into the structure-dynamics properties, including confirmation of a preferential Li+-carbonyl oxygen atom coordination, with a preference in coordination to the ester based monomers. A coupling of the Li-ion dynamics to the polymer chain dynamics was indicated by both simulations and experiments.
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| 26. |
- Shwan, Soran, 1984
(författare)
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Metal-exchanged zeolites for NH3-SCR applications - Activity and Deactivation studies
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emissions of nitrogen oxides (NOX) formed during the burning process in internal combustion engines is a major contributor to global air pollutions. One effective way to reduce NOX in lean environments, i.e. oxygen excess is selective catalytic reduction with ammonia (NH3-SCR). Metal-exchanged zeolites have proven to be active as SCR catalysts, where copper and iron are the most common metals. When using metal-exchanged zeolites in exhaust aftertreatment systems, several challenges arise. Resistance towards hydrothermal deactivation and chemisorption of impurities on the active sites of the catalyst are two of the more important challenges. Temperatures between 600-700oC can be seen during regeneration of the particulate filter, which usually is placed upstream close to the SCR catalyst in the exhaust aftertreatment system, and therefore hydrothermal stability of the metal-exchanged zeolite is crucial. Furthermore, high tolerance against catalyst poisons which originate from (bio-) fuels and lubricating oils is desired, where phosphorous and potassium are among the more important poisons. In this thesis thermal and chemical deactivation of iron-exchanged zeolite BEA as SCR catalyst is experimentally studied with special focus paid on the active iron species. Based on the experimental results a kinetic model is developed to predict the decreased activity of the catalyst after deactivation. Several characterization techniques are used to evaluate and correlate structural changes in the catalyst with the decreased activity. Catalysts are prepared and characterized using BET, XPS, XRD, TPD, in-situ FTIR and UV-Vis. The catalytic performance of the samples is measured using a flow-reactor system.It is concluded that the hydrothermal deactivation of Fe-BEA is a result of migration of isolated iron species forming iron cluster inside the zeolite pores and iron particles located on the external surface of the zeolite crystals. Further, it is shown that the growth of iron clusters and particles can be partially reversed by high temperature hydrogen treatment. The chemical deactivation due to phosphorous exposure is the result of formation of metaphosphates replacing hydroxyl groups on the active isolated iron species. Furthermore, the chemical deactivation of Fe-BEA by potassium is concluded to be due to exchange and loss of active isolated iron species in the zeolite forming smaller iron clusters inside the zeolite pores.A kinetic model where different iron species are included was developed based on the hydrothermal deactivation experiments and validated using phosphorous and potassium exposed samples. By fitting and fix the kinetic parameters towards a fresh sample, the decreased SCR activity can be predicted by just decreasing the number of active iron sites, representing loss of active iron species due to hydrothermal treatment and poisoning.The effect of gas atmosphere during solid-state ion-exchange of copper-zeolites was studied as well. It is concluded that copper becomes highly mobile due to formation of copper-ammine complexes in presence of NH3 after reduction of CuII to CuI by adding NO in the exposing gas during the solid-state ion-exchange. Copper-exchanged zeolites could be prepared by exposing physical mixtures of copper-oxides with zeolites to NO and NH3 at as low temperature as 250oC.Finally, the ammonia formation during the rich period of NOX storage and reduction (NSR) cycles was studied using kinetic modeling for the possibility of combining NSR and SCR catalysts in the exhaust aftertreatment system. It is concluded that the formation of ammonia is due to stored NOX and hydrogen from the gas in the first half of the catalyst. However, it was further concluded that the formation of ammonia is delayed due to formation of N2O from stored NOX and formed NH3.
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| 27. |
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| 28. |
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| 29. |
- Qiao, K., et al.
(författare)
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Size-resolved effective density of submicron particles during summertime in the rural atmosphere of Beijing, China
- 2018
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Ingår i: Journal of Environmental Sciences. - : Elsevier BV. - 1001-0742. ; 73, s. 69-77
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Tidskriftsartikel (refereegranskat)abstract
- Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm(3), on average. The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm(3) for 50 to 350 nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6 g/cm(3) for 150, 240, and 350 nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation (NPF) event decreased considerably, indicating the significant contribution of organics to new particle growth. (C) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
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| 30. |
- Hassellöv, Martin, 1970, et al.
(författare)
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REACH missar nano!
- 2009
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Ingår i: Miljöforskning. ; 2009:3-4
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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