scholarly journals Kaolinite particles as ice nuclei: learning from the use of different kaolinite samples and different coatings

2014 ◽  
Vol 14 (11) ◽  
pp. 5529-5546 ◽  
Author(s):  
H. Wex ◽  
P. J. DeMott ◽  
Y. Tobo ◽  
S. Hartmann ◽  
M. Rösch ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Succinic Acid ◽  
Freezing Point ◽  
Active Surface ◽  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Rate Coefficients ◽  
Ice Nuclei ◽  
Ability To Act ◽  
Immersion Freezing

Abstract. Kaolinite particles from two different sources (Fluka and Clay Minerals Society (CMS)) were examined with respect to their ability to act as ice nuclei (IN). This was done in the water-subsaturated regime where often deposition ice nucleation is assumed to occur, and for water-supersaturated conditions, i.e., in the immersion freezing mode. Measurements were done using a flow tube (the Leipzig Aerosol Cloud Interaction Simulator, LACIS) and a continuous-flow diffusion chamber (CFDC). Pure and coated particles were used, with coating thicknesses of a few nanometers or less, where the coating consisted of levoglucosan, succinic acid or sulfuric acid. In general, it was found that the coatings strongly reduced deposition ice nucleation. Remaining ice formation in the water-subsaturated regime could be attributed to immersion freezing, with particles immersed in concentrated solutions formed by the coatings. In the immersion freezing mode, ice nucleation rate coefficients jhet from both instruments agreed well with each other, particularly when the residence times in the instruments were accounted for. Fluka kaolinite particles coated with either levoglucosan or succinic acid showed the same IN activity as pure Fluka kaolinite particles; i.e., it can be assumed that these two types of coating did not alter the ice-active surface chemically, and that the coatings were diluted enough in the droplets that were formed prior to the ice nucleation, so that freezing point depression was negligible. However, Fluka kaolinite particles, which were either coated with pure sulfuric acid or were first coated with the acid and then exposed to additional water vapor, both showed a reduced ability to nucleate ice compared to the pure particles. For the CMS kaolinite particles, the ability to nucleate ice in the immersion freezing mode was similar for all examined particles, i.e., for the pure ones and the ones with the different types of coating. Moreover, jhet derived for the CMS kaolinite particles was comparable to jhet derived for Fluka kaolinite particles coated with sulfuric acid. This is suggestive for the Fluka kaolinite possessing a type of ice-nucleating surface feature which is not present on the CMS kaolinite, and which can be destroyed by reaction with sulfuric acid. This might be potassium feldspar.

scholarly journals Kaolinite particles as ice nuclei: learning from the use of different types of kaolinite and different coatings

2013 ◽  
Vol 13 (11) ◽  
pp. 30311-30348 ◽  
Author(s):  
H. Wex ◽  
P. J. DeMott ◽  
Y. Tobo ◽  
S. Hartmann ◽  
M. Rösch ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Succinic Acid ◽  
Freezing Point ◽  
Active Surface ◽  
Ice Nucleation ◽  
Rate Coefficients ◽  
Ice Nuclei ◽  
Ability To Act ◽  
Different Types ◽  
Immersion Freezing

Abstract. Kaolinite particles from two different sources (Fluka and Clay Minerals Society (CMS)) were examined with respect to their ability to act as ice nuclei. This was done in the water subsaturated regime where often deposition ice nucleation is assumed to occur, and for water supersaturated conditions, i.e. in the immersion freezing mode. Measurements were done using a flow tube (LACIS) and a continuous flow diffusion chamber (CFDC). Pure and coated particles were used, with coating thicknesses of a few nanometer or less, where the coating consisted of either levoglucosan, succinic acid, or sulfuric acid. In general, it was found that the coatings strongly reduced deposition ice nucleation. Remaining ice formation in the water subsaturated regime could be attributed to immersion freezing, with particles immersed in concentrated solutions formed by the coatings. In the immersion freezing mode, ice nucleation rate coefficients, jhet, from both instruments agreed with each other when the residence times in the instruments were accounted for. Fluka kaolinite particles coated with either levoglucosan or succinic acid showed the same IN activity as pure Fluka kaolinite particles, i.e. it can be assumed that these two types of coating did not alter the ice active surface chemically, and that the coatings were diluted enough in the droplets that were formed prior to the ice nucleation, so that freezing point depression was negligible. However, Fluka kaolinite particles which were coated with either pure sulfuric acid or which were first coated with the acid and then exposed to additional water vapor both showed a reduced ability to nucleate ice, compared to the pure particles. For the CMS kaolinite particles, the ability to nucleate ice in the immersion freezing mode was similar for all examined particles, i.e. for the pure ones and the ones with the different types of coating. Moreover, jhet derived for the CMS kaolinite particles was comparable to jhet derived for kaolinite particles coated with sulfuric acid. This is suggestive for the Fluka kaolinite possessing a type of ice nucleating surface feature which is not present on the CMS kaolinite, and which can be destroyed by reaction with sulfuric acid, which might be potassium feldspar.

scholarly journals Ice nucleation properties of fine ash particles from the Eyjafjallajökull eruption in April 2010

2011 ◽  
Vol 11 (6) ◽  
pp. 17665-17698 ◽  
Author(s):  
I. Steinke ◽  
O. Möhler ◽  
A. Kiselev ◽  
M. Niemand ◽  
H. Saathoff ◽  
...  
Keyword(s):  
Volcanic Ash ◽  
Active Surface ◽  
Ice Nucleation ◽  
Saharan Dust ◽  
Surface Site ◽  
Ice Nuclei ◽  
Active Surface Site ◽  
Mineral Dusts ◽  
Immersion Freezing ◽  
Ice Fraction

Abstract. During the eruption of the Eyjafjallajökull volcano in the south of Iceland in April/May 2010, about 40 Tg of ash mass were emitted into the atmosphere. However, it was unclear whether volcanic ash particles with d < 10 μm facilitate the glaciation of clouds. Thus, ice nucleation properties of volcanic ash particles were investigated in AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber experiments simulating atmospherically relevant conditions. The ash sample that was used for our experiments had been collected at a distance of 58 km from the Eyjafjallajökull during the eruption period in April 2010. The temperature range covered by our ice nucleation experiments extended from 219 to 264 K, and both ice nucleation via immersion freezing and deposition nucleation could be observed. Immersion freezing was first observed at 252 K, whereas the deposition nucleation onset lay at 242 K and RHice = 126 %. About 0.1 % of the volcanic ash particles were active as immersion freezing nuclei at a temperature of 249 K. For deposition nucleation, an ice fraction of 0.1 % was observed at around 233 K and RHice = 116 %. Taking ice-active surface site densities as a measure for the ice nucleation efficiency, volcanic ash particles are similarly efficient ice nuclei in immersion freezing mode (ns, imm ~ 109 m−2 at 247 K) compared to certain mineral dusts. For deposition nucleation, the observed ice-active surface site densities ns, dep were found to be 1011 m−2 at 224 K and RHice = 116 %. Thus, volcanic ash particles initiate deposition nucleation more efficiently than Asian and Saharan dust but appear to be poorer ice nuclei than ATD particles. Based on the experimental data, we have derived ice-active surface site densities as a function of temperature for immersion freezing and of relative humidity over ice and temperature for deposition nucleation.

scholarly journals Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

2005 ◽  
Vol 5 (3) ◽  
pp. 3391-3436 ◽  
Author(s):  
C. M. Archuleta ◽  
P. J. DeMott ◽  
S. M. Kreidenweis
Keyword(s):  
Sulfuric Acid ◽  
Relative Humidity ◽  
Mineral Dust ◽  
Aerosol Particles ◽  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Nucleation Behavior ◽  
Ice Nuclei ◽  
Homogeneous Freezing

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between −45 and −60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.

scholarly journals Ice nucleation by surrogates for atmospheric mineral dust and mineral dust/sulfate particles at cirrus temperatures

2005 ◽  
Vol 5 (10) ◽  
pp. 2617-2634 ◽  
Author(s):  
C. M. Archuleta ◽  
P. J. DeMott ◽  
S. M. Kreidenweis
Keyword(s):  
Sulfuric Acid ◽  
Relative Humidity ◽  
Mineral Dust ◽  
Aerosol Particles ◽  
Diffusion Chamber ◽  
Ice Nucleation ◽  
Dust Particles ◽  
Nucleation Behavior ◽  
Ice Nuclei ◽  
Homogeneous Freezing

Abstract. This study examines the potential role of some types of mineral dust and mineral dust with sulfuric acid coatings as heterogeneous ice nuclei at cirrus temperatures. Commercially-available nanoscale powder samples of aluminum oxide, alumina-silicate and iron oxide were used as surrogates for atmospheric mineral dust particles, with and without multilayer coverage of sulfuric acid. A sample of Asian dust aerosol particles was also studied. Measurements of ice nucleation were made using a continuous-flow ice-thermal diffusion chamber (CFDC) operated to expose size-selected aerosol particles to temperatures between -45 and -60°C and a range of relative humidity above ice-saturated conditions. Pure metal oxide particles supported heterogeneous ice nucleation at lower relative humidities than those required to homogeneously freeze sulfuric acid solution particles at sizes larger than about 50 nm. The ice nucleation behavior of the same metal oxides coated with sulfuric acid indicate heterogeneous freezing at lower relative humidities than those calculated for homogeneous freezing of the diluted particle coatings. The effect of soluble coatings on the ice activation relative humidity varied with the respective uncoated core particle types, but for all types the heterogeneous freezing rates increased with particle size for the same thermodynamic conditions. For a selected size of 200 nm, the natural mineral dust particles were the most effective ice nuclei tested, supporting heterogeneous ice formation at an ice relative humidity of approximately 135%, irrespective of temperature. Modified homogeneous freezing parameterizations and theoretical formulations are shown to have application to the description of heterogeneous freezing of mineral dust-like particles with soluble coatings.

scholarly journals Ice nucleation properties of fine ash particles from the Eyjafjallajökull eruption in April 2010

2011 ◽  
Vol 11 (24) ◽  
pp. 12945-12958 ◽  
Author(s):  
I. Steinke ◽  
O. Möhler ◽  
A. Kiselev ◽  
M. Niemand ◽  
H. Saathoff ◽  
...  
Keyword(s):  
Volcanic Ash ◽  
Active Surface ◽  
Ice Nucleation ◽  
Saharan Dust ◽  
Surface Site ◽  
Ice Nuclei ◽  
Active Surface Site ◽  
Mineral Dusts ◽  
Immersion Freezing ◽  
Ice Fraction

Abstract. During the eruption of the Eyjafjallajökull volcano in the south of Iceland in April/May 2010, about 40 Tg of ash mass were emitted into the atmosphere. It was unclear whether volcanic ash particles with d < 10 μm facilitate the glaciation of clouds. Thus, ice nucleation properties of volcanic ash particles were investigated in AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber experiments simulating atmospherically relevant conditions. The ash sample that was used for our experiments had been collected at a distance of 58 km from the Eyjafjallajökull during the eruption period in April 2010. The temperature range covered by our ice nucleation experiments extended from 219 to 264 K, and both ice nucleation via immersion freezing and deposition nucleation could be observed. Immersion freezing was first observed at 252 K, whereas the deposition nucleation onset lay at 242 K and RHice =126%. About 0.1% of the volcanic ash particles were active as immersion freezing nuclei at a temperature of 249 K. For deposition nucleation, an ice fraction of 0.1% was observed at around 233 K and RHice =116%. Taking ice-active surface site densities as a measure for the ice nucleation efficiency, volcanic ash particles are similarly efficient ice nuclei in immersion freezing mode (ns,imm ~ 109 m−2 at 247 K) compared to certain mineral dusts. For deposition nucleation, the observed ice-active surface site densities ns,dep were found to be 1011 m−2 at 224 K and RHice =116%. Thus, volcanic ash particles initiate deposition nucleation more efficiently than Asian and Saharan dust but appear to be poorer ice nuclei than ATD particles. Based on the experimental data, we have derived ice-active surface site densities as a function of temperature for immersion freezing and of relative humidity over ice and temperature for deposition nucleation.

scholarly journals Ice nucleation efficiency of AgI: review and new insights

2016 ◽  
Author(s):  
Claudia Marcolli ◽  
Baban Nagare ◽  
André Welti ◽  
Ulrike Lohmann
Keyword(s):  
Water Saturation ◽  
Experimental Studies ◽  
Freezing Temperature ◽  
Nucleating Agent ◽  
Companion Paper ◽  
Chem Phys ◽  
Ice Nucleation ◽  
Lattice Match ◽  
Ice Nuclei ◽  
Immersion Freezing

Abstract. AgI is one of the best investigated ice nuclei. It has relevance for the atmosphere since it is used for glaciogenic cloud seeding. Theoretical and experimental studies over the last sixty years provide a complex picture of silver iodide as ice nucleating agent with conflicting and inconsistent results. This review compares experimental ice nucleation studies in order to analyse the factors that influence the ice nucleation ability of AgI. We have performed experiments to compare contact and immersion freezing by AgI. This is one of three papers that describe and analyse contact and immersion freezing experiments with AgI. In Nagare et al. (Nagare, B., Marcolli, C., Stetzer, O., and Lohmann, U.: Comparison of measured and calculated collision efficiencies at low temperatures, Atmos. Chem. Phys., 15, 13759–13776, doi:10.5194/acp-15-13759-2015, 2015) collision efficiencies based on contact freezing experiments with AgI are determined and compared with theoretical formulations. In a companion paper, contact freezing experiments are compared with immersion freezing experiments conducted with AgI, kaolinite, and ATD as ice nuclei. The following picture emerges from this analysis: The ice nucleation ability of AgI seems to be enhanced when the AgI particle is on the surface of a droplet, which is indeed the position that a particle takes when it can freely move in a droplet. Ice nucleation by particles with surfaces exposed to air, depends on water adsorption. AgI surfaces seem to be most efficient as ice nuclei when they are exposed to relative humidity at or even above water saturation. For AgI particles that are totally immersed in water, the freezing temperature increases with increasing AgI surface area. Higher threshold freezing temperature seem to correlate with improved lattice matches as can be seen for AgI-AgCl solid solutions and 3AgI•NH4I•6H2O, which have slightly better lattice matches with ice than AgI and also higher threshold freezing temperatures. However, the effect of a good lattice match is annihilated when the surfaces have charges. Also, the ice nucleation ability seems to decrease during dissolution of AgI particles. This introduces an additional history and time dependence of ice nucleation in cloud chambers with short residence times.

scholarly journals A comprehensive characterization of ice nucleation by three different types of cellulose particles immersed in water

2019 ◽  
Vol 19 (7) ◽  
pp. 4823-4849 ◽  
Author(s):  
Naruki Hiranuma ◽  
Kouji Adachi ◽  
David M. Bell ◽  
Franco Belosi ◽  
Hassan Beydoun ◽  
...  
Keyword(s):  
Aqueous Suspension ◽  
Measurement Techniques ◽  
Active Surface ◽  
Ice Nucleation ◽  
Accuracy And Precision ◽  
Active Surface Site ◽  
Two Samples ◽  
Order Of Magnitude ◽  
Immersion Freezing ◽  
T Values

Abstract. We present the laboratory results of immersion freezing efficiencies of cellulose particles at supercooled temperature (T) conditions. Three types of chemically homogeneous cellulose samples are used as surrogates that represent supermicron and submicron ice-nucleating plant structural polymers. These samples include microcrystalline cellulose (MCC), fibrous cellulose (FC) and nanocrystalline cellulose (NCC). Our immersion freezing dataset includes data from various ice nucleation measurement techniques available at 17 different institutions, including nine dry dispersion and 11 aqueous suspension techniques. With a total of 20 methods, we performed systematic accuracy and precision analysis of measurements from all 20 measurement techniques by evaluating T-binned (1 ∘C) data over a wide T range (−36 ∘C <T<-4 ∘C). Specifically, we intercompared the geometric surface area-based ice nucleation active surface site (INAS) density data derived from our measurements as a function of T, ns,geo(T). Additionally, we also compared the ns,geo(T) values and the freezing spectral slope parameter (Δlog(ns,geo)/ΔT) from our measurements to previous literature results. Results show all three cellulose materials are reasonably ice active. The freezing efficiencies of NCC samples agree reasonably well, whereas the diversity for the other two samples spans ≈ 10 ∘C. Despite given uncertainties within each instrument technique, the overall trend of the ns,geo(T) spectrum traced by the T-binned average of measurements suggests that predominantly supermicron-sized cellulose particles (MCC and FC) generally act as more efficient ice-nucleating particles (INPs) than NCC with about 1 order of magnitude higher ns,geo(T).

scholarly journals Effect of particle surface area on ice active site densities retrieved from droplet freezing spectra

2016 ◽  
Vol 16 (20) ◽  
pp. 13359-13378 ◽  
Author(s):  
Hassan Beydoun ◽  
Michael Polen ◽  
Ryan C. Sullivan
Keyword(s):  
Surface Area ◽  
Active Sites ◽  
Particle Surface ◽  
Active Surface ◽  
Freezing Temperature ◽  
Ice Nucleation ◽  
Critical Surface ◽  
Cold Plate ◽  
Particle Surface Area ◽  
Immersion Freezing

Abstract. Heterogeneous ice nucleation remains one of the outstanding problems in cloud physics and atmospheric science. Experimental challenges in properly simulating particle-induced freezing processes under atmospherically relevant conditions have largely contributed to the absence of a well-established parameterization of immersion freezing properties. Here, we formulate an ice active, surface-site-based stochastic model of heterogeneous freezing with the unique feature of invoking a continuum assumption on the ice nucleating activity (contact angle) of an aerosol particle's surface that requires no assumptions about the size or number of active sites. The result is a particle-specific property g that defines a distribution of local ice nucleation rates. Upon integration, this yields a full freezing probability function for an ice nucleating particle. Current cold plate droplet freezing measurements provide a valuable and inexpensive resource for studying the freezing properties of many atmospheric aerosol systems. We apply our g framework to explain the observed dependence of the freezing temperature of droplets in a cold plate on the concentration of the particle species investigated. Normalizing to the total particle mass or surface area present to derive the commonly used ice nuclei active surface (INAS) density (ns) often cannot account for the effects of particle concentration, yet concentration is typically varied to span a wider measurable freezing temperature range. A method based on determining what is denoted an ice nucleating species' specific critical surface area is presented and explains the concentration dependence as a result of increasing the variability in ice nucleating active sites between droplets. By applying this method to experimental droplet freezing data from four different systems, we demonstrate its ability to interpret immersion freezing temperature spectra of droplets containing variable particle concentrations. It is shown that general active site density functions, such as the popular ns parameterization, cannot be reliably extrapolated below this critical surface area threshold to describe freezing curves for lower particle surface area concentrations. Freezing curves obtained below this threshold translate to higher ns values, while the ns values are essentially the same from curves obtained above the critical area threshold; ns should remain the same for a system as concentration is varied. However, we can successfully predict the lower concentration freezing curves, which are more atmospherically relevant, through a process of random sampling from g distributions obtained from high particle concentration data. Our analysis is applied to cold plate freezing measurements of droplets containing variable concentrations of particles from NX illite minerals, MCC cellulose, and commercial Snomax bacterial particles. Parameterizations that can predict the temporal evolution of the frozen fraction of cloud droplets in larger atmospheric models are also derived from this new framework.

scholarly journals Deposition and immersion-mode nucleation of ice by three distinct samples of volcanic ash

2015 ◽  
Vol 15 (13) ◽  
pp. 7523-7536 ◽  
Author(s):  
G. P. Schill ◽  
K. Genareau ◽  
M. A. Tolbert
Keyword(s):  
Volcanic Ash ◽  
Mineral Dust ◽  
Global Climate ◽  
Volcanic Eruptions ◽  
Silica Content ◽  
Ice Nucleation ◽  
Ice Nuclei ◽  
Immersion Freezing ◽  
Nucleation Activity ◽  
Ice Nucleation Activity

Abstract. Ice nucleation of volcanic ash controls both ash aggregation and cloud glaciation, which affect atmospheric transport and global climate. Previously, it has been suggested that there is one characteristic ice nucleation efficiency for all volcanic ash, regardless of its composition, when accounting for surface area; however, this claim is derived from data from only two volcanic eruptions. In this work, we have studied the depositional and immersion freezing efficiency of three distinct samples of volcanic ash using Raman microscopy coupled to an environmental cell. Ash from the Fuego (basaltic ash, Guatemala), Soufrière Hills (andesitic ash, Montserrat), and Taupo (Oruanui eruption, rhyolitic ash, New Zealand) volcanoes were chosen to represent different geographical locations and silica content. All ash samples were quantitatively analyzed for both percent crystallinity and mineralogy using X-ray diffraction. In the present study, we find that all three samples of volcanic ash are excellent depositional ice nuclei, nucleating ice from 225 to 235 K at ice saturation ratios of 1.05 ± 0.01, comparable to the mineral dust proxy kaolinite. Since depositional ice nucleation will be more important at colder temperatures, fine volcanic ash may represent a global source of cold-cloud ice nuclei. For immersion freezing relevant to mixed-phase clouds, however, only the Oruanui ash exhibited appreciable heterogeneous ice nucleation activity. Similar to recent studies on mineral dust, we suggest that the mineralogy of volcanic ash may dictate its ice nucleation activity in the immersion mode.

scholarly journals Ice nucleation properties of K-feldspar polymorphs and plagioclase feldspars

2019 ◽  
Author(s):  
André Welti ◽  
Ulrike Lohmann ◽  
Zamin A. Kanji
Keyword(s):  
Trace Elements ◽  
Elemental Composition ◽  
Ice Nucleation ◽  
Cloud Properties ◽  
Ability To Act ◽  
Mineralogical Characteristics ◽  
Trace Elemental ◽  
Mineral Dusts ◽  
Immersion Freezing ◽  
Ice Nucleation Activity

Abstract. The relation between the mineralogical characteristics of size selected feldspar particles from 50–800 nm and their ability to act as ice nucleating particles (INPs) in the immersion mode is presented. Five polymorph members of K-feldspar (two microclines, orthoclase, adularia and sanidine) and four Na/Ca- rich feldspar samples (three labradorites and a pericline sample) are tested. Microcline was found to be the most active INP in the immersion mode consistent with previous findings. Samples are selected for their differences in typical feldspar properties such as crystal structure, bulk and trace elemental composition and ordering of the crystal lattice. The mentioned properties are related to the temperature of feldspar crystallization from the melt rocks during formation. Properties characteristic for low temperature feldspar formation coincide with an increased ability to nucleate ice. Ice nucleation is most efficient on the crystallographic ordered, triclinic K-feldspar species microcline, while the intermediate and disordered, monoclinic K-feldspar polymorphs orthoclase and sanidine nucleate ice at lower temperatures. The ice nucleation ability of disordered, triclinic Na/Ca-feldspar is comparable to disordered K-feldspar. The conditions of feldspar rock formation also leave a chemical fingerprint with varying abundance of trace elements in the samples. X-ray fluorescence spectroscopy analysis to determine metal oxide and trace elemental composition of the feldspar samples revealed a correlation with median freezing temperatures (T50) of the K-feldspar samples allowing to sort them for their ice nucleation efficiency according to the abundance of specific trace elements. A pronounced size dependence of ice nucleation activity for the feldspar samples is observed, which also depends on mineralogical characteristics. In particular, microcline exhibited immersion freezing even for 50 nm particles which is unique for heterogeneous ice nucleation of mineral dusts. This suggests that small microcline particles that are susceptible to long-range transport can affect cloud properties via immersion freezing far away from the source. The measurements generally imply that temperatures at which feldspars can affect cloud glaciation depends on the transported particle size.

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