| 1. |
- Bartels-Rausch, T., et al.
(författare)
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A review of air-ice chemical and physical interactions (AICI): Liquids, quasi-liquids, and solids in snow
- 2014
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 14:3, s. 1587-1633
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Tidskriftsartikel (refereegranskat)abstract
- Snow in the environment acts as a host to rich chemistry and provides a matrix for physical exchange of contaminants within the ecosystem. The goal of this review is to summarise the current state of knowledge of physical processes and chemical reactivity in surface snow with relevance to polar regions. It focuses on a description of impurities in distinct compartments present in surface snow, such as snow crystals, grain boundaries, crystal surfaces, and liquid parts. It emphasises the microscopic description of the ice surface and its link with the environment. Distinct differences between the disordered air-ice interface, often termed quasi-liquid layer, and a liquid phase are highlighted. The reactivity in these different compartments of surface snow is discussed using many experimental studies, simulations, and selected snow models from the molecular to the macro-scale. Although new experimental techniques have extended our knowledge of the surface properties of ice and their impact on some single reactions and processes, others occurring on, at or within snow grains remain unquantified. The presence of liquid or liquid-like compartments either due to the formation of brine or disorder at surfaces of snow crystals below the freezing point may strongly modify reaction rates. Therefore, future experiments should include a detailed characterisation of the surface properties of the ice matrices. A further point that remains largely unresolved is the distribution of impurities between the different domains of the condensed phase inside the snowpack, i.e. in the bulk solid, in liquid at the surface or trapped in confined pockets within or between grains, or at the surface. While surface-sensitive laboratory techniques may in the future help to resolve this point for equilibrium conditions, additional uncertainty for the environmental snowpack may be caused by the highly dynamic nature of the snowpack due to the fast metamorphism occurring under certain environmental conditions. Due to these gaps in knowledge the first snow chemistry models have attempted to reproduce certain processes like the long-term incorporation of volatile compounds in snow and firn or the release of reactive species from the snowpack. Although so far none of the models offers a coupled approach of physical and chemical processes or a detailed representation of the different compartments, they have successfully been used to reproduce some field experiments. A fully coupled snow chemistry and physics model remains to be developed. © Author(s) 2014.
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| 2. |
- Bartels-Rausch, T., et al.
(författare)
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Interfacial supercooling and the precipitation of hydrohalite in frozen NaCl solutions as seen by X-ray absorption spectroscopy
- 2021
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0416. ; 15:4, s. 2001-2020
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory experiments are presented on the phase change at the surface of sodium chloride-water mixtures at temperatures between 259 and 241 K. Chloride is a ubiquitous component of polar coastal surface snow. The chloride embedded in snow is involved in reactions that modify the chemical composition of snow as well as ultimately impact the budget of trace gases and the oxidative capacity of the overlying atmosphere. Multiphase reactions at the snow-air interface have been of particular interest in atmospheric science. Undoubtedly, chemical reactions proceed faster in liquids than in solids; but it is currently unclear when such phase changes occur at the interface of snow with air. In the experiments reported here, a high selectivity to the upper few nanometres of the frozen solution-air interface is achieved by using electron yield near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. We find that sodium chloride at the interface of frozen solutions, which mimic sea-salt deposits in snow, remains as supercooled liquid down to 241 K. At this temperature, hydrohalite exclusively precipitates and anhydrous sodium chloride is not detected. In this work, we present the first NEXAFS spectrum of hydrohalite. The hydrohalite is found to be stable while increasing the temperature towards the eutectic temperature of 252 K. Taken together, this study reveals no differences in the phase changes of sodium chloride at the interface as compared to the bulk. That sodium chloride remains liquid at the interface upon cooling down to 241 K, which spans the most common temperature range in Arctic marine environments, has consequences for interfacial chemistry involving chlorine as well as for any other reactant for which the sodium chloride provides a liquid reservoir at the interface of environmental snow. Implications for the role of surface snow in atmospheric chemistry are discussed. © 2021 BMJ Publishing Group. All rights reserved.
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| 3. |
- Hong, A. C., et al.
(författare)
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Uptake of Hydrogen Peroxide from the Gas Phase to Grain Boundaries: A Source in Snow and Ice
- 2023
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Ingår i: Environmental Science and Technology. - 0013-936X .- 1520-5851. ; 57:31, s. 11626-11633
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Tidskriftsartikel (refereegranskat)abstract
- This work shows that hydrogen peroxidereadily enters grainboundaries in ice and snow directly from the atmosphere. Acceleratedreaction rates in these reservoirs have been described with an impacton air quality and snow composition. Hydrogen peroxide is a primary atmospheric oxidant significantin terminating gas-phase chemistry and sulfate formation in the condensedphase. Laboratory experiments have shown an unexpected oxidation accelerationby hydrogen peroxide in grain boundaries. While grain boundaries arefrequent in natural snow and ice and are known to host impurities,it remains unclear how and to which extent hydrogen peroxide entersthis reservoir. We present the first experimental evidence for thediffusive uptake of hydrogen peroxide into grain boundaries directlyfrom the gas phase. We have machined a novel flow reactor system featuringa drilled ice flow tube that allows us to discern the effect of theice grain boundary content on the uptake. Further, adsorption to theice surface for temperatures from 235 to 258 K was quantified. Disentanglingthe contribution of these two uptake processes shows that the transferof hydrogen peroxide from the atmosphere to snow at temperatures relevantto polar environments is considerably more pronounced than previouslythought. Further, diffusive uptake to grain boundaries appears tobe a novel mechanism for non-acidic trace gases to fill the highlyreactive impurity reservoirs in snow's grain boundaries.
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| 4. |
- Kong, Xiangrui, et al.
(författare)
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Coexistence of Physisorbed and Solvated HCI at Warm Ice Surfaces
- 2017
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Ingår i: Journal of Physical Chemistry Letters. - 1948-7185. ; 8:19, s. 4757-4762
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial ionization of strong acids is an essential factor of multiphase and heterogeneous chemistry in environmental science, cryospheric science, catalysis research and material science. Using near ambient pressure core level X-ray photoelectron spectroscopy, we directly detected a low surface coverage of adsorbed HCl at 253 K in both molecular and dissociated states. Depth profiles derived from XPS data indicate the results as physisorbed molecular HCl at the outermost ice surface and dissociation occurring upon solvation deeper in the interfacial region. Complementary X-ray absorption measurements confirm that the presence of ions induces significant changes to the hydrogen bonding network in the interfacial region. This study gives clear evidence for nonuniformity across the air ice interface and questions the use of acid base concepts in interfacial processes.
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| 5. |
- Kong, Xiangrui, et al.
(författare)
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Adsorbed Water Promotes Chemically Active Environments on the Surface of Sodium Chloride
- 2023
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Ingår i: Journal of Physical Chemistry Letters. - 1948-7185. ; 14:26, s. 6151-6156
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Tidskriftsartikel (refereegranskat)abstract
- Gas-particleinterfaces are chemically active environments.This study investigates the reactivity of SO2 on NaCl surfacesusing advanced experimental and theoretical methods with a NH4Cl substrate also examined for cation effects. Results showthat NaCl surfaces rapidly convert to Na2SO4 with a new chlorine component when exposed to SO2 underlow humidity. In contrast, NH4Cl surfaces have limitedSO(2) uptake and do not change significantly. Depth profilesreveal transformed layers and elemental ratios at the crystal surfaces.The chlorine species detected originates from Cl- expelled from the NaCl crystal structure, as determined by atomisticdensity functional theory calculations. Molecular dynamics simulationshighlight the chemically active NaCl surface environment, driven bya strong interfacial electric field and the presence of sub-monolayerwater coverage. These findings underscore the chemical activity ofsalt surfaces and the unexpected chemistry that arises from theirinteraction with interfacial water, even under very dry conditions.
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| 6. |
- Orlando, F., et al.
(författare)
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Disordered Adsorbed Water Layers on TiO2 Nanoparticles under Subsaturated Humidity Conditions at 235 K
- 2019
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:23, s. 7433-7438
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of water with TiO2 is of substantial scientific and technological interest as it determines the activity of TiO2 in photocatalytic and environmental applications in nanoparticle suspensions in water, in complex appliances, or in pure form interacting with water vapor. The influence of TiO2 nanoparticles on the hydrogen bonding structure of water molecules is an important factor that controls hydration of other species, reactions, or nucleation processes. We use a combination of ambient-pressure X-ray photoelectron spectroscopy and electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the oxygen K-edge to investigate the hydrogen bonding structure of adsorbed water on titania nanoparticles in equilibrium with nearly saturated water vapor at 235 K. The results clearly show that the net NEXAFS spectrum of adsorbed water resembles that of liquid, disordered water at 235 K, a temperature at which both homogeneous and heterogeneous freezing of bulk water is anticipated.
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