A comparative study of K-rich and Na/Ca-rich feldspar ice nucleating particles in a nanoliter droplet freezing assay

Peckhaus, Andreas; Kiselev, Alexei; Hiron, Thibault; Ebert, Martin; Leisner, Thomas

doi:10.5194/acp-2016-72

Cited by 12 publications

(39 citation statements)

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“…D p1 : droplet diameter with on average 1 particle inside (µm); p het : calculated heterogeneously frozen water volume fraction assuming that droplets containing particles froze heterogeneously; p het,lab : measured heterogeneously frozen water volume fraction; f act (0.5)/f act (2): ratio of f act determined for 0.5 and 2 wt % suspensions; f act (2)/f act (10): ratio of f act determined for 2 and 10 wt % suspensions. Reference samples are from this study and from Pinti et al (2012). Emulsion freezing experiments were carried out with suspension concentrations of 0.5 wt % (triangles), 1 wt % (circles), 2 wt % (squares), 5 wt % (diamonds), and 10 wt % (pentagons).…”

Section: Mineralsmentioning

confidence: 99%

“…Illite references (illite SE and illite NX) exhibit broad peaks with maxima at 239-242 K and can account for heterogeneous freezing up to 246 K with an active fraction of 0.18 and 0.12, respectively. Pinti et al (2012) and Atkinson et al (2013) report illite as major component of illite NX and illite SE together with minor fractions of feldspar, however, without specifying the exact type of feldspar. The heterogeneous freezing signal in the DSC thermograms of illite SE and illite NX arises most probably from the main illite component of the sample.…”

Section: Freezing Experimentsmentioning

confidence: 99%

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Ice nucleation efficiency of natural dust samples in the immersion mode

Kaufmann¹,

Marcolli²,

Hofer³

et al. 2016

Preprint

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Abstract. Twelve natural dust samples from eight dust source regions on four continents were investigated with respect to their ice nucleation activity, revealing no significant differences between source regions. Dust collection sites were distributed across Africa, South America, the Middle East and Antarctica. Mineralogical compositions have been determined by means of X-ray diffraction. All samples proved to be mixtures of minerals, with major contributions from quartz, calcite, clay minerals, K-feldspars and (Na, Ca)-feldspars. Reference samples of these minerals were investigated with the same methods as the natural dust samples. Furthermore, Arizona Test Dust (ATD) was re-evaluated as a benchmark. Immersion freezing of emulsion and bulk samples was investigated by differential scanning calorimetry. For emulsion measurements, water droplets with a diameter of about 2 &#181;m, containing different amounts of dust between 0.5 wt% and 50 wt% were cooled until all droplets were frozen. These measurements characterize the average freezing behaviour of particles, as they are sensitive to the average active sites present in a dust sample. In addition, bulk measurements were conducted with one single 1 mm diameter droplet consisting of a 5 wt% aqueous suspension of the dusts/minerals. These measurements allow the investigation of the best particles/sites available in a dust. All natural dusts except for the Antarctica and ATD samples froze in a remarkably narrow temperature range with the heterogeneously frozen fraction reaching 10 % between 244 and 250 K, 25 % between 242 and 246 K, and 50 % between 239 and 244 K. Bulk freezing occurred between 255 and 265 K. In contrast to the natural dusts, the reference minerals reveal ice nucleation temperatures with 2&#8211;3 times larger scatter. Calcite, dolomite, dolostone and muscovite can be considered inactive as ice nuclei (IN). For microcline samples 50 % heterogeneously frozen fraction occurred above 245 K for all tested suspension concentrations, and a microcline mineral showed bulk freezing temperatures even above 270 K. This makes microcline (KAlSi3O8) an exceptionally good IN, superior to all other analysed K-feldspars, (Na, Ca)-feldspars and the clay minerals. However, microcline is not abundant in the investigated natural dust samples. While K-feldspars were identified in five of the seven investigated natural source regions, only one sample contained microcline, and then only as a minor fraction. In summary, the mineralogical composition can explain the observed freezing behaviour of five of the investigated 12 natural dust samples, and partly for six samples, leaving the freezing efficiency of only one sample not easily explained in terms of its mineral reference components. While this suggests that mineralogical composition is a major determinant of ice nucleation ability, in practice most natural samples consist of a mixture of minerals, and this mixture seems to lead to remarkably similar ice nucleation abilities, regardless of their exact composition, so that global models, in a first approximation, may represent mineral dust as a single species with respect to ice nucleation activity. However, more sophisticated representations of ice nucleation by mineral dusts should rely on the mineralogical composition based on a source scheme of dust emissions.

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Section: Mineralsmentioning

confidence: 99%

Section: Freezing Experimentsmentioning

confidence: 99%

Ice nucleation efficiency of natural dust samples in the immersion mode

Kaufmann¹,

Marcolli²,

Hofer³

et al. 2016

Preprint

View full text Add to dashboard Cite

show abstract

“…The second group are Kfeldspars (adularia, microcline, orthoclase, and sanidine), which proved to have a high ice nucleation efficiency (Atkinson et al, 2013;Emersic et al, 2015;Zolles et al, 2015;Harrison et al, 2016;Peckhaus et al, 2016). The third group consists of (Na, Ca)-feldspars (anorthite, labradorite, albite (pericline), and plagioclase, not further specified), which have been reported to be quite efficient as INPs (Atkinson et al, 2013;Augustin-Bauditz et al, 2014;Zolles et al, 2015;Peckhaus et al, 2016), though less efficient than Kfeldspars. The fourth group are clay minerals: DSC freezing experiments of illite, kaolinite, and montmorillonite (member of the smectite group) have been performed by Pinti et al (2012) and can be used here as references for clay minerals.…”

Section: Reference Mineralsmentioning

confidence: 99%

“…Moreover, the presence of biological material has been discussed to increase the ice nucleation ability of dusts Baker et al, 2005;Pratt et al, 2009;Conen et al, 2011;Hallar et al, 2011;Creamean et al, 2013). Peckhaus et al (2016) investigated four milled feldspar minerals in freezing experiments. Bulk mineralogical composition determined by XRD revealed the three K-rich samples to consist mainly of microcline (76-80 %) with a minor (Na, Ca)-feldspar component (16-24 %).…”

Section: Active Particle Fraction F Actmentioning

confidence: 99%

Ice nucleation efficiency of natural dust samples in the immersion mode

et al. 2016

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Abstract. A total of 12 natural surface dust samples, which were surface-collected on four continents, most of them in dust source regions, were investigated with respect to their ice nucleation activity. Dust collection sites were distributed across Africa, South America, the Middle East, and Antarctica. Mineralogical composition has been determined by means of X-ray diffraction. All samples proved to be mixtures of minerals, with major contributions from quartz, calcite, clay minerals, K-feldspars, and (Na, Ca)-feldspars. Reference samples of these minerals were investigated with the same methods as the natural dust samples. Furthermore, Arizona test dust (ATD) was re-evaluated as a benchmark. Immersion freezing of emulsion and bulk samples was investigated by differential scanning calorimetry. For emulsion measurements, water droplets with a size distribution peaking at about 2 µm, containing different amounts of dust between 0.5 and 50 wt % were cooled until all droplets were frozen. These measurements characterize the average freezing behaviour of particles, as they are sensitive to the average active sites present in a dust sample. In addition, bulk measurements were conducted with one single 2 mg droplet consisting of a 5 wt % aqueous suspension of the dusts/minerals. These measurements allow the investigation of the best icenucleating particles/sites available in a dust sample. All natural dusts, except for the Antarctica and ATD samples, froze in a remarkably narrow temperature range with the heterogeneously frozen fraction reaching 10 % between 244 and 250 K, 25 % between 242 and 246 K, and 50 % between 239 and 244 K. Bulk freezing occurred between 255 and 265 K. In contrast to the natural dusts, the reference minerals revealed ice nucleation temperatures with 2-3 times larger scatter. Calcite, dolomite, dolostone, and muscovite can be considered ice nucleation inactive. For microcline samples, a 50 % heterogeneously frozen fraction occurred above 245 K for all tested suspension concentrations, and a microcline mineral showed bulk freezing temperatures even above 270 K. This makes microcline (KAlSi 3 O 8 ) an exceptionally good ice-nucleating mineral, superior to all other analysed K-feldspars, (Na, Ca)-feldspars, and the clay minerals. In summary, the mineralogical composition can explain the observed freezing behaviour of 5 of the investigated 12 natural dust samples, and partly for 6 samples, leaving the freezing efficiency of only 1 sample not easily explained in terms of its mineral reference components. While this suggests that mineralogical composition is a major determinant of ice-nucleating ability, in practice, most natural samples consist of a mixture of minerals, and this mixture seems to lead to remarkably similar ice nucleation abilities, regardless of their exact composition, so that global models, in a first approximation, may represent mineral dust as a single species with respect to ice nucleation activity. However, more sophisticated representations of ice nucleation by mineral dusts...

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“…Hoggar Mountain dust was collected from the Sahara region (Pinti et al, 2012). It is a mixture of minerals originating from a source region with high shares of clay minerals (Pinti et al, 2012).…”

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A comparative study of K-rich and Na/Ca-rich feldspar ice nucleating particles in a nanoliter droplet freezing assay

Cited by 12 publications

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Ice nucleation efficiency of natural dust samples in the immersion mode

Ice nucleation efficiency of natural dust samples in the immersion mode

Ice nucleation efficiency of natural dust samples in the immersion mode

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