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  • 1
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 2016
    In:  Journal of Geophysical Research: Planets Vol. 121, No. 5 ( 2016-05), p. 753-769
    In: Journal of Geophysical Research: Planets, American Geophysical Union (AGU), Vol. 121, No. 5 ( 2016-05), p. 753-769
    Abstract: Measurements on heterogeneous nucleation of CO 2 on meteoric smoke particle analogues Evaluation of contact parameter, desorption energy, and sticking coefficient Extreme cold conditions are needed to affect CO 2 nucleation in the Martian mesosphere
    Type of Medium: Online Resource
    ISSN: 2169-9097 , 2169-9100
    URL: Issue
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2016
    detail.hit.zdb_id: 1086497-0
    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 2016810-X
    SSG: 16,13
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  • 2
    Online Resource
    Online Resource
    Copernicus GmbH ; 2018
    In:  Atmospheric Chemistry and Physics Vol. 18, No. 5 ( 2018-03-08), p. 3419-3431
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 18, No. 5 ( 2018-03-08), p. 3419-3431
    Abstract: Abstract. The crystallization of amorphous solid water (ASW) is known to form nano-crystalline ice. The influence of the nanoscale crystallite size on physical properties like the vapor pressure is relevant for processes in which the crystallization of amorphous ices occurs, e.g., in interstellar ices or cold ice cloud formation in planetary atmospheres, but up to now is not well understood. Here, we present laboratory measurements on the saturation vapor pressure over ice crystallized from ASW between 135 and 190 K. Below 160 K, where the crystallization of ASW is known to form nano-crystalline ice, we obtain a saturation vapor pressure that is 100 to 200 % higher compared to stable hexagonal ice. This elevated vapor pressure is in striking contrast to the vapor pressure of stacking disordered ice which is expected to be the prevailing ice polymorph at these temperatures with a vapor pressure at most 18 % higher than that of hexagonal ice. This apparent discrepancy can be reconciled by assuming that nanoscale crystallites form in the crystallization process of ASW. The high curvature of the nano-crystallites results in a vapor pressure increase that can be described by the Kelvin equation. Our measurements are consistent with the assumption that ASW is the first solid form of ice deposited from the vapor phase at temperatures up to 160 K. Nano-crystalline ice with a mean diameter between 7 and 19 nm forms thereafter by crystallization within the ASW matrix. The estimated crystal sizes are in agreement with reported crystal size measurements and remain stable for hours below 160 K. Thus, this ice polymorph may be regarded as an independent phase for many atmospheric processes below 160 K and we parameterize its vapor pressure using a constant Gibbs free energy difference of (982 ± 182) J mol−1 relative to hexagonal ice.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 2092549-9
    detail.hit.zdb_id: 2069847-1
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  • 3
    Online Resource
    Online Resource
    Informa UK Limited ; 2015
    In:  Aerosol Science and Technology Vol. 49, No. 9 ( 2015-09-02), p. 683-691
    In: Aerosol Science and Technology, Informa UK Limited, Vol. 49, No. 9 ( 2015-09-02), p. 683-691
    Type of Medium: Online Resource
    ISSN: 0278-6826 , 1521-7388
    Language: English
    Publisher: Informa UK Limited
    Publication Date: 2015
    detail.hit.zdb_id: 2023330-9
    detail.hit.zdb_id: 787246-X
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  • 4
    Online Resource
    Online Resource
    American Chemical Society (ACS) ; 2023
    In:  The Journal of Physical Chemistry B
    In: The Journal of Physical Chemistry B, American Chemical Society (ACS)
    Type of Medium: Online Resource
    ISSN: 1520-6106 , 1520-5207
    RVK:
    Language: English
    Publisher: American Chemical Society (ACS)
    Publication Date: 2023
    detail.hit.zdb_id: 1357799-2
    detail.hit.zdb_id: 2006039-7
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  • 5
    Online Resource
    Online Resource
    Copernicus GmbH ; 2019
    In:  Atmospheric Chemistry and Physics Vol. 19, No. 19 ( 2019-10-11), p. 12767-12777
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 19 ( 2019-10-11), p. 12767-12777
    Abstract: Abstract. Accurate determination of the optical properties of analogues for meteoric smoke particles (MSPs), which are thought to be composed of iron-rich oxides or silicates, is important for their observation and characterization in the atmosphere. In this study, a photochemical aerosol flow system (PAFS) has been used to measure the optical extinction of iron oxide MSP analogues in the wavelength range 325–675 nm. The particles were made photochemically and agglomerate into fractal-like particles with sizes on the order of 100 nm. Analysis using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) suggested the particles were most likely maghemite-like (γ-Fe2O3) in composition, though a magnetite-like composition could not be completely ruled out. Assuming a maghemite-like composition, the optical extinction coefficients measured using the PAFS were combined with maghemite absorption coefficients measured using a complementary experimental system (the MICE-TRAPS) to derive complex refractive indices that reproduce both the measured absorption and extinction.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2092549-9
    detail.hit.zdb_id: 2069847-1
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  • 6
    Online Resource
    Online Resource
    Copernicus GmbH ; 2019
    In:  Atmospheric Chemistry and Physics Vol. 19, No. 5 ( 2019-03-06), p. 2871-2879
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 5 ( 2019-03-06), p. 2871-2879
    Abstract: Abstract. Polar mesospheric clouds are the highest water ice clouds occurring in the terrestrial atmosphere. They form in the polar summer mesopause, the coldest region in the atmosphere. It has long been assumed that these clouds form by heterogeneous nucleation on meteoric smoke particles which are the remnants of material ablated from meteoroids in the upper atmosphere. However, until now little was known about the properties of these nanometre-sized particles and application of the classical theory for heterogeneous ice nucleation was impacted by large uncertainties. In this work, we performed laboratory measurements on the heterogeneous ice formation process at mesopause conditions on small (r=1 to 3 nm) iron silicate nanoparticles serving as meteoric smoke analogues. We observe that ice growth on these particles sets in for saturation ratios with respect to hexagonal ice below Sh=50, a value that is commonly exceeded during the polar mesospheric cloud season, affirming meteoric smoke particles as likely nuclei for heterogeneous ice formation in mesospheric clouds. We present a simple ice-activation model based on the Kelvin–Thomson equation that takes into account the water coverage of iron silicates of various compositions. The activation model reproduces the experimental data very well using bulk properties of compact amorphous solid water. This is in line with the finding from our previous study that ice formation on iron silicate nanoparticles occurs by condensation of amorphous solid water rather than by nucleation of crystalline ice at mesopause conditions. Using the activation model, we also show that for iron silicate particles with dry radius larger than r=0.6 nm the nanoparticle charge has no significant effect on the ice-activation threshold.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2092549-9
    detail.hit.zdb_id: 2069847-1
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  • 7
    Online Resource
    Online Resource
    Copernicus GmbH ; 2019
    In:  Atmospheric Chemistry and Physics Vol. 19, No. 7 ( 2019-04-03), p. 4311-4322
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 19, No. 7 ( 2019-04-03), p. 4311-4322
    Abstract: Abstract. Mean temperatures in the polar summer mesopause can drop to 130 K. The low temperatures in combination with water vapor mixing ratios of a few parts per million give rise to the formation of ice particles. These ice particles may be observed as polar mesospheric clouds. Mesospheric ice cloud formation is believed to initiate heterogeneously on small aerosol particles (r〈2 nm) composed of recondensed meteoric material, so-called meteoric smoke particles (MSPs). Recently, we investigated the ice activation and growth behavior of MSP analogues under realistic mesopause conditions. Based on these measurements we presented a new activation model which largely reduced the uncertainties in describing ice particle formation. However, this activation model neglected the possibility that MSPs heat up in the low-density mesopause due to absorption of solar and terrestrial irradiation. Radiative heating of the particles may severely reduce their ice formation ability. In this study we expose MSP analogues (Fe2O3 and FexSi1−xO3) to realistic mesopause temperatures and water vapor concentrations and investigate particle warming under the influence of variable intensities of visible light (405, 488, and 660 nm). We show that Mie theory calculations using refractive indices of bulk material from the literature combined with an equilibrium temperature model presented in this work predict the particle warming very well. Additionally, we confirm that the absorption efficiency increases with the iron content of the MSP material. We apply our findings to mesopause conditions and conclude that the impact of solar and terrestrial radiation on ice particle formation is significantly lower than previously assumed.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2092549-9
    detail.hit.zdb_id: 2069847-1
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  • 8
    Online Resource
    Online Resource
    American Chemical Society (ACS) ; 2018
    In:  The Journal of Physical Chemistry B Vol. 122, No. 43 ( 2018-11-01), p. 10044-10050
    In: The Journal of Physical Chemistry B, American Chemical Society (ACS), Vol. 122, No. 43 ( 2018-11-01), p. 10044-10050
    Type of Medium: Online Resource
    ISSN: 1520-6106 , 1520-5207
    RVK:
    Language: English
    Publisher: American Chemical Society (ACS)
    Publication Date: 2018
    detail.hit.zdb_id: 1357799-2
    detail.hit.zdb_id: 2006039-7
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  • 9
    Online Resource
    Online Resource
    AIP Publishing ; 2019
    In:  The Journal of Chemical Physics Vol. 151, No. 6 ( 2019-08-14)
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 151, No. 6 ( 2019-08-14)
    Abstract: In the atmosphere, water can be present in liquid and solid phases, but the vapor phase is generally predominant. Condensed phases of water occur under a wide range of conditions, ranging from polar mesospheric clouds at the lowest atmospheric temperatures and at low pressure to the much warmer tropospheric clouds. The temperature range at which ice or water clouds are observed spans from T = 100 to 300 K with pressures ranging from about 10−3 mbar to about 1 bar. Over this wide range, water is known to form several condensed phases, which can be separated into crystalline (hexagonal and stacking disordered ice) and noncrystalline phases (liquid and supercooled liquid water, amorphous solid water). We report on the vapor pressure of these water phases with a focus on metastable amorphous solid water and stacking disordered ice in the light of recent experimental findings and discuss possible implications for the atmosphere. We present evidence that supercooled liquid water and low density amorphous solid water do not belong to the same phase and therefore, no continuous vapor pressure curve can be given.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 10
    Online Resource
    Online Resource
    Walter de Gruyter GmbH ; 2018
    In:  Zeitschrift für Physikalische Chemie Vol. 232, No. 5-6 ( 2018-5-24), p. 635-648
    In: Zeitschrift für Physikalische Chemie, Walter de Gruyter GmbH, Vol. 232, No. 5-6 ( 2018-5-24), p. 635-648
    Abstract: The article reports on the composition, mixing state and water affinity of iron silicate particles which were produced in a non-thermal low-pressure microwave plasma reactor. The particles are intended to be used as meteoric smoke particle analogues. We used the organometallic precursors ferrocene (Fe(C 5 H 5 ) 2 ) and tetraethyl orthosilicate (TEOS, Si(OC 2 H 5 ) 4 ) in various mixing ratios to produce nanoparticles with radii between 1 nm and 4 nm. The nanoparticles were deposited on sample grids and their stoichiometric composition was analyzed in an electron microscope using energy dispersive X-ray spectroscopy (EDS). We show that the pure silicon oxide and iron oxide particles consist of SiO 2 and Fe 2 O 3 , respectively. For Fe:(Fe+Si) ratios between 0.2 and 0.8 our reactor produces (in contrast to other particle sources) mixed iron silicates with a stoichiometric composition according to Fe x Si (1−x) O 3 (0≤x≤1). This indicates that the particles are formed by polymerization of FeO 3 and SiO 3 and that rearrangement to the more stable silicates ferrosilite (FeSiO 3 ) and fayalite (Fe 2 SiO 4 ) does not occur at these conditions. To investigate the internal mixing state of the particles, the H 2 O surface desorption energy of the particles was measured. We found that the nanoparticles are internally mixed and that differential coating resulting in a core-shell structure does not occur.
    Type of Medium: Online Resource
    ISSN: 2196-7156 , 0942-9352
    RVK:
    Language: English
    Publisher: Walter de Gruyter GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 201103-7
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