Coal fly ash: linking immersion freezing behavior and physicochemical particle properties

Grawe, Sarah; Augustin-Bauditz, Stefanie; Clemen, Hans-Christian; Ebert, Martin; Hammer, Stine Eriksen; Lubitz, Jasmin; Reicher, Nàama; Rudich, Yinon; Schneider, Johannes; Staacke, Robert; Stratmann, Frank; Welti, André; Wex, Heike

doi:10.5194/acp-18-13903-2018

Cited by 35 publications

(52 citation statements)

References 63 publications

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“…A number of laboratory facilities for aerosol and cloud research, such as aerosol-cloud chambers, continuous-flow systems, wind tunnels and electrodynamic balances have been developed and used over the last decades for atmospheric research (a detailed compilation of, and references for, atmospheric chambers and facilities is given in Chang et al, 2016, andCziczo et al, 2017). At TROPOS, we developed the laminar flow tube LACIS (Leipzig Aerosol Cloud Interaction Simulator; Stratmann et al, 2004;Hartmann et al, 2011) which has been applied for the investigation of aerosol-cloud interaction processes under controllable and reproducible conditions in a continuous-flow setting. Investigations using LACIS comprised the consistent descriptions of both hygroscopic growth and droplet activation for various inorganic (Wex et al, 2005;Niedermeier et al, 2008) and organic materials such as HULIS (humic-like substances; Wex et al, 2007;Ziese et al, 2008), secondary organic aerosol Petters et al, 2009) and soot particles Stratmann et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol–cloud–turbulence interactions

et al. 2020

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Abstract. The interactions between turbulence and cloud microphysical processes have been investigated primarily through numerical simulation and field measurements over the last 10 years. However, only in the laboratory we can be confident in our knowledge of initial and boundary conditions and are able to measure under statistically stationary and repeatable conditions. In the scope of this paper, we present a unique turbulent moist-air wind tunnel, called the Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T) which has been developed at TROPOS in order to study cloud physical processes in general and interactions between turbulence and cloud microphysical processes in particular. The investigations take place under well-defined and reproducible turbulent and thermodynamic conditions covering the temperature range of warm, mixed-phase and cold clouds (25∘C>T>-40∘C). The continuous-flow design of the facility allows for the investigation of processes occurring on small temporal (up to a few seconds) and spatial scales (micrometer to meter scale) and with a Lagrangian perspective. The here-presented experimental studies using LACIS-T are accompanied and complemented by computational fluid dynamics (CFD) simulations which help us to design experiments as well as to interpret experimental results. In this paper, we will present the fundamental operating principle of LACIS-T, the numerical model, and results concerning the thermodynamic and flow conditions prevailing inside the wind tunnel, combining both characterization measurements and numerical simulations. Finally, the first results are depicted from deliquescence and hygroscopic growth as well as droplet activation and growth experiments. We observe clear indications of the effect of turbulence on the investigated microphysical processes.

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Section: Introductionmentioning

confidence: 99%

Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol–cloud–turbulence interactions

et al. 2020

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“…soot particles (Mahrt et al, 2018), but less active compared to some biological materials (Suski et al, 2018). Their ice-nucleating abilities are similar to the ice-nucleating potential of some mineral components of desert or agricultural soil dusts (Grawe et al, 2018;Umo et al, 20 2015).…”

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confidence: 99%

“…proportion is injected into the atmosphere -hence, they could contribute to heterogeneous ice formation in clouds. Previously, CFA particles have been shown to nucleate ice in the immersion mode (Grawe et al, 2016(Grawe et al, , 2018Umo et al, 2015). However, there are variabilities in the ice nucleation activities of the different CFA samples reported, which could be due to the difference in mineralogical compositions; as well as variabilities in the actual freezing mechanisms, which could be influenced by surface defects or porosity of the particles.…”

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Enhanced ice nucleation activity of coal fly ash aerosol particles initiated by ice-filled pores

Umo¹,

Wagner²,

Ullrich³

et al. 2019

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<p><strong>Abstract.</strong> Ice-nucleating particles (INPs), which are precursors for ice formation in clouds, can alter the microphysical and optical properties of clouds, hence, impacting the cloud lifetimes and hydrological cycles. However, the mechanisms with which these INPs nucleate ice when exposed to different atmospheric conditions are still unclear for some particles. Recently, some INPs with pores or permanent surface defects of regular or irregular geometries have been reported to initiate ice formation at cirrus temperatures via the liquid phase in a two-step process, involving the condensation and freezing of supercooled water inside these pores. This mechanism has therefore been labelled as pore condensation and freezing (PCF). The PCF mechanism allows formation and stabilization of ice germs in the particle without the formation of macroscopic ice. Coal fly ash (CFA) aerosol particles are known to nucleate ice in the immersion freezing mode and may play a significant role in cloud formation. In our current ice nucleation experiments with CFA particles, which we conducted in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) aerosol and cloud simulation chamber at the Karlsruhe Institute of Technology, Germany, we partly observed a strong increase in the ice-active fraction for experiments performed at temperatures just below the homogeneous freezing of pure water, which could be related to the PCF mechanism. To further investigate the potential of CFA particles undergoing PCF mechanism, we performed a series of temperature-cycling experiments in AIDA. The temperature-cycling experiments involve exposing CFA particles to lower temperatures (down to ~&#8201;228&#8201;K), then warming them up to higher temperatures (238&#8201;K&#8211;273&#8201;K) before investigating their ice nucleation properties. For the first time, we report the enhancement of the ice nucleation activity of the CFA particles for temperatures up to 263&#8201;K, from which we conclude that it is most likely due to the PCF mechanism. This indicates that ice germs formed in the CFA particles&#8217; pores during cooling remains in the pores during the warming and induces ice crystallization as soon as the pre-activated particles experience ice-supersaturated conditions at warmer temperatures; hence, showing an enhancement in their ice-nucleating ability compared to the scenario where the CFA particles are directly probed at warmer temperatures without temporary cooling. The enhancement in the ice nucleation ability showed a positive correlation with the specific surface area and porosity of the particles. On the one hand, the PCF mechanism could be the prevalent nucleation mode for intrinsic ice formation at cirrus temperatures rather than the previously acclaimed deposition mode. On the other, the PCF mechanism can also play a significant role in mixed-phase cloud formation in a case where the CFA particles are injected from higher altitudes and then transported to lower altitudes after being exposed to lower temperatures.</p>

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“…The evaporation column was not capped at the bottom, to allow the exhaust air to escape and avoid turbulence. Finally, fibre-like particles were wet-generated from a suspension of coal burning sourced fly ash particles and Milli-Q water, using an atomizer, as described in more detail in Grawe et al (2016Grawe et al ( , 2018.…”

Section: Ppd-hs Calibration Measurementsmentioning

confidence: 99%

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Mahrt¹

2019

Preprint

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A new instrument, the High Speed Particle Phase Discriminator (PPD-HS) developed at the University of Hertfordshire, for sizing individual cloud hydrometeors and determining their phase is described herein. PPD-HS performs an in-situ analysis of the spatial intensity distribution of near forward scattered light for individual hydrometeors yielding shape properties. Discrimination of spherical and aspherical particles is based on an analysis of the symmetry of the recorded scattering patterns. Scattering patterns are collected onto two linear detector arrays, reducing the complete 2D scattering pattern to scattered light intensities captured onto two linear, one dimensional strips of light sensitive pixels. Using this reduced scattering information, we calculate symmetry indicators that are used for particle shape and ultimately phase analysis. This reduction of information allows for detection rates of a few hundred particles per second. Here, we present a comprehensive analysis of instrument performance using both spherical and aspherical particles, generated in a well-controlled laboratory setting using a Vibrating Orifice Aerosol Generator (VOAG) and covering a size range of approximately 3 − 32 µm. We use supervised machine learning to train a random forest model on the VOAG data sets that can be used to classify any particles detected by PPD-HS. Classification results show that the PPD-HS can successfully discriminate between spherical and aspherical particles, with misclassification below 5 % for diameters > 3 µm. This phase discrimination method is subsequently applied to classify simulated cloud particles produced in a continuous flow diffusion chamber setup. We report observations of small, near-spherical ice crystals at early stages of the ice nucleation experiments, where shape analysis fails to correctly determine the particle phase. Nevertheless, in case of simultaneous presence of cloud droplets and ice crystals, the introduced particle shape indicators allow for a clear distinction between these two classes independent of optical particle size. We conclude that PPD-HS constitutes a powerful new instrument to size and discriminate phase of cloud hydrometeors and thus study microphysical properties of mixed-phase clouds, that represent a major source of uncertainty in aerosol indirect effect for future climate projections.

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Coal fly ash: linking immersion freezing behavior and physicochemical particle properties

Cited by 35 publications

References 63 publications

Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol–cloud–turbulence interactions

Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol–cloud–turbulence interactions

Enhanced ice nucleation activity of coal fly ash aerosol particles initiated by ice-filled pores

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