An improved approach for measuring immersion freezing in large droplets over a wide temperature range

Tobo, Yutaka

doi:10.1038/srep32930

Cited by 68 publications

(100 citation statements)

References 49 publications

(143 reference statements)

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“…1; more details in Supplement). A cold-stage is a dropfreezing apparatus, on which droplets are deposited onto a cooling surface and the temperature at which they freeze is observed (Vali, 1971a). This technique is commonly used today to assess the activation temperature of INPs immersed in droplets.…”

Section: Single Crystal Selection and Analysismentioning

confidence: 99%

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

et al. 2019

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Ice crystal numbers can exceed the numbers of icenucleating particles (INPs) observed in mixed-phase clouds (MPCs) by several orders of magnitude, also at temperatures that are colder than − 8 • C. This disparity provides circumstantial evidence of secondary ice formation, also other than via the Hallett-Mossop process. In a new approach, we made use of the fact that planar, branched ice crystals (e.g. dendrites) grow within a relatively narrow temperature range (i.e. −12 to −17 • C) and can be analysed individually for INPs using a field-deployable drop-freezing assay. The novelty of our approach lies in comparing the growth temperature encoded in the habit of an individual crystal with the activation temperature of the most efficient INP contained within the same crystal to tell whether it may be the result of primary ice formation. In February and March 2018, we analysed a total of 190 dendritic crystals (∼ 3 mm median size) deposited within MPCs at the high-altitude research station Jungfraujoch (3580 m a.s.l.). Overall, one in eight of the analysed crystals contained an INP active at −17 • C or warmer, while the remaining seven most likely resulted from secondary ice formation within the clouds. The ice multiplication factor we observed was small (8), but relatively stable throughout the course of documentation. These measurements show that secondary ice can be observed at temperatures around −15 • C and thus advance our understanding of the extent of secondary ice formation in MPCs, even where the multiplication factor is smaller than 10.

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Section: Single Crystal Selection and Analysismentioning

confidence: 99%

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

et al. 2019

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“…The Cryogenic Refrigerator Applied to Freezing Test (CRAFT) device has been described in detail by Tobo (2016). CRAFT is a classical cold-plate device akin to the DFT and the CS instruments, but it involves procedures to assure sample isolation, primarily from the cold-plate surface using a layer of Vaseline ® .…”

Section: National Institute Of Polar Research Craftmentioning

confidence: 99%

Comparative measurements of ambient atmospheric concentrations of ice nucleating particles using multiple immersion freezing methods and a continuous flow diffusion chamber

et al. 2017

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Abstract. A number of new measurement methods for ice nucleating particles (INPs) have been introduced in recent years, and it is important to address how these methods compare. Laboratory comparisons of instruments sampling major INP types are common, but few comparisons have occurred for ambient aerosol measurements exploring the utility, consistency and complementarity of different methods to cover the large dynamic range of INP concentrations that exists in the atmosphere. In this study, we assess the comparability of four offline immersion freezing measurement methods (Colorado State University ice spectrometer, IS; North Carolina State University cold stage, CS; National Institute for Polar Research Cryogenic Refrigerator Applied to Freezing Test, CRAFT; University of British Columbia microorifice uniform deposit impactor-droplet freezing technique, MOUDI-DFT) and an online method (continuous flow diffusion chamber, CFDC) used in a manner deemed to promote/maximize immersion freezing, for the detection of INPs in ambient aerosols at different locations and in different sampling scenarios. We also investigated the comparability of different aerosol collection methods used with offline immersion freezing instruments. Excellent agreement between all methods could be obtained for several cases of co-sampling with perfect temporal overlap. Even for sampling periods that were not fully equivalent, the deviations between atmospheric INP number concentrations measured with different methods were mostly less than 1 order of magnitude. In some cases, however, the deviations were larger and not explicable without sampling and measurement artifacts. Overall, the immersion freezing methods seem toPublished by Copernicus Publications on behalf of the European Geosciences Union. , although more comparisons are needed in this temperature regime that is difficult to access with online methods. Relative to the CFDC method, three immersion freezing methods that disperse particles into a bulk liquid (IS, CS, CRAFT) exhibit a positive bias in measured INP number concentrations below −20 • C, increasing with decreasing temperature. This bias was present but much less pronounced for a method that condenses separate water droplets onto limited numbers of particles prior to cooling and freezing (MOUDI-DFT). Potential reasons for the observed differences are discussed, and further investigations proposed to elucidate the role of all factors involved.

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“…Immersion mode freezing was tested using a drop freezing assay (DFA) cold plate apparatus. This cold plate technique was based on previous but slightly modified apparatuses Stopelli et al, 2014;Tobo, 2016;. For brevity, we call this system the NOAA drop freezing cold plate (DFCP).…”

Section: Offline Ice Nucleation Analyses 241 Drop Freezing Assay Fomentioning

confidence: 99%

“…Copper discs (76 mm in diameter, 3.2 mm thick) were prepared by cleaning with isopropanol (99.5 % ACS Grade, LabChem. Inc.), then coated with a thin layer of petrolatum (100 %, Vaseline ® ) (Bowers et al, 2009;Tobo, 2016). Three of the spots on the filter had visible aerosol deposits that were successfully transferred to the UPW (i.e., based on visual identification).…”

Section: Offline Ice Nucleation Analyses 241 Drop Freezing Assay Fomentioning

confidence: 99%

“…4). Materials tested were chosen based on those used in previous work and included (1) direct petrolatum (Tobo, 2016), (2) 15 % w/v petrolatum in xylenes (Certified ACS Reagent Grade, Ricca Chemical) (Bowers et al, 2009), (3) silicone fluid (710 fluid, Dow Corning ® ) (Polen et al, 2016), and (4) squalene (≥ 98 %, Sigma-Aldrich ® ) (Hader et al, 2014;. The silicone fluid was difficult to use for cold plate experimentation because droplets would coalesce during the experiment and freezing detection by eye was difficult due to the glare of the substance.…”

Section: Offline Ice Nucleation Analyses 241 Drop Freezing Assay Fomentioning

confidence: 99%

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HOVERCAT: a novel aerial system for evaluation of aerosol–cloud interactions

et al. 2018

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Abstract. Aerosols have a profound impact on cloud microphysics through their ability to serve as ice nucleating particles (INPs). As a result, cloud radiative properties and precipitation processes can be modulated by such aerosolcloud interactions. However, one of the largest uncertainties associated with atmospheric processes is the indirect effect of aerosols on clouds. The need for more advanced observations of INPs in the atmospheric vertical profile is apparent, yet most ice nucleation measurements are conducted on the ground or during infrequent and intensive airborne field campaigns. Here, we describe a novel measurement platform that is less expensive and smaller (< 5 kg) when compared to traditional aircraft and tethered balloon platforms and that can be used for evaluating two modes of ice nucleation (i.e., immersion and deposition). HOVERCAT (Honing On VERtical Cloud and Aerosol properTies) flew during a pilot study in Colorado, USA, up to 2.6 km above mean sea level (1.1 km above ground level) and consists of an aerosol module that includes an optical particle counter for size distributions (0.38-17 µm in diameter) and a new sampler that collects up to 10 filter samples for offline ice nucleation and aerosol analyses on a launched balloon platform. During the May 2017 test flight, total particle concentrations were highest closest to the ground (up to 50 cm −3 at < 50 m above ground level) and up to 2 in 10 2 particles were ice nucleation active in the immersion mode (at −23 • C). The warmest temperature immersion and deposition mode INPs (observed up to −6 and −40.4 • C, respectively) were observed closest to the ground, but overall INP concentrations did not exhibit an inverse correlation with increasing altitude. HOVERCAT is a prototype that can be further modified for other airborne platforms, including tethered balloon and unmanned aircraft systems. The versatility of HOVERCAT affords future opportunities to profile the atmospheric column for more comprehensive evaluations of aerosol-cloud interactions. Based on our test flight experiences, we provide a set of recommendations for future deployments of similar measurement systems and platforms.

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An improved approach for measuring immersion freezing in large droplets over a wide temperature range

Cited by 68 publications

References 49 publications

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

Comparative measurements of ambient atmospheric concentrations of ice nucleating particles using multiple immersion freezing methods and a continuous flow diffusion chamber

HOVERCAT: a novel aerial system for evaluation of aerosol–cloud interactions

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