scholarly journals An instrument for quantifying heterogeneous ice nucleation in multiwell plates using infrared emissions to detect freezing

2018 ◽  
Author(s):  
Alexander D. Harrison ◽  
Thomas F. Whale ◽  
Rupert Rutledge ◽  
Stephen Lamb ◽  
Mark D. Tarn ◽  
...  
Keyword(s):  
Active Sites ◽  
Freezing Temperature ◽  
Equilibrium Temperature ◽  
High Time Resolution ◽  
Ir Camera ◽  
Low Concentrations ◽  
Initial Nucleation ◽  
Report Data ◽  
Immersion Freezing ◽  
Mixed Phase Clouds

Abstract. Low concentrations of ice nucleating particles (INPs) are thought to be important for the properties of mixed-phase clouds, but their detection is challenging. While instruments to quantify INPs online can provide relatively high time resolution data, they typically cannot quantify very low INP concentrations. Furthermore, typical online instruments tend to report data at a single defined set of conditions. Hence, there is a need for instruments where INP concentrations of less than 0.01 L−1 can be routinely and efficiently determined. The use of larger volumes of suspension in drop assays increases the sensitivity of an experiment to rarer INPs or rarer active sites due to the increase in aerosol or surface area of particulates per droplet. Here we describe and characterise the InfraRed-Nucleation by Immersed Particles Instrument (IR-NIPI), a new immersion freezing assay that makes use of IR emissions to determine the freezing temperature of individual 50 μL droplets each contained in a well of a 96-well plate. Using an IR camera allows the temperature of individual aliquots to be monitored. Freezing temperatures are determined by detecting the sharp rise in well temperature associated with the release of latent the release of heat caused by freezing. In this paper we first present the calibration of the IR temperature measurement, which makes use of the freezing period after initial nucleation when wells warm and their temperature is determined by the ice-liquid equilibrium temperature, i.e. 0 °C when the water activity is ~ 1. We then tested the temperature calibration using ~ 100 µm chips of K-feldspar, by immersing these chips in 1 µL droplets on an established cold stage (µL-NIPI) as well as in 50 µL droplets on IR-NIPI; the results were consistent with one another indicating no bias in the reported freezing temperature. In addition we present measurements of the efficiency of the mineral dust NX-illite and a sample of atmospheric aerosol collected on a filter in the city of Leeds. NX-illite results are consistent with literature data and the atmospheric INP concentrations were in good agreement with the results from the µL-NIPI instrument. This demonstrates the utility of this approach, which offers a relatively high throughput of sample analysis and access to low INP concentrations.

scholarly journals An instrument for quantifying heterogeneous ice nucleation in multiwell plates using infrared emissions to detect freezing

2018 ◽  
Vol 11 (10) ◽  
pp. 5629-5641 ◽  
Author(s):  
Alexander D. Harrison ◽  
Thomas F. Whale ◽  
Rupert Rutledge ◽  
Stephen Lamb ◽  
Mark D. Tarn ◽  
...  
Keyword(s):  
Active Sites ◽  
Freezing Temperature ◽  
Equilibrium Temperature ◽  
Ice Nucleation ◽  
Ir Camera ◽  
Low Concentrations ◽  
Immersion Freezing ◽  
Mixed Phase Clouds ◽  
The City ◽  
Good Agreement

Abstract. Low concentrations of ice-nucleating particles (INPs) are thought to be important for the properties of mixed-phase clouds, but their detection is challenging. Hence, there is a need for instruments where INP concentrations of less than 0.01 L−1 can be routinely and efficiently determined. The use of larger volumes of suspension in drop assays increases the sensitivity of an experiment to rarer INPs or rarer active sites due to the increase in aerosol or surface area of particulates per droplet. Here we describe and characterise the InfraRed-Nucleation by Immersed Particles Instrument (IR-NIPI), a new immersion freezing assay that makes use of IR emissions to determine the freezing temperature of individual 50 µL droplets each contained in a well of a 96-well plate. Using an IR camera allows the temperature of individual aliquots to be monitored. Freezing temperatures are determined by detecting the sharp rise in well temperature associated with the release of heat caused by freezing. In this paper we first present the calibration of the IR temperature measurement, which makes use of the fact that following ice nucleation aliquots of water warm to the ice–liquid equilibrium temperature (i.e. 0 ∘C when water activity is ∼1), which provides a point of calibration for each individual well in each experiment. We then tested the temperature calibration using ∼100 µm chips of K-feldspar, by immersing these chips in 1 µL droplets on an established cold stage (µL-NIPI) as well as in 50 µL droplets on IR-NIPI; the results were consistent with one another, indicating no bias in the reported freezing temperature. In addition we present measurements of the efficiency of the mineral dust NX-illite and a sample of atmospheric aerosol collected on a filter in the city of Leeds. NX-illite results are consistent with literature data, and the atmospheric INP concentrations were in good agreement with the results from the µL-NIPI instrument. This demonstrates the utility of this approach, which offers a relatively high throughput of sample analysis and access to low INP concentrations.

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 Comparative Study On Immersion Freezing Utilizing Single Droplet Levitation Methods

2020 ◽  
Author(s):  
Miklós Szakáll ◽  
Michael Debertshäuser ◽  
Christian Philipp Lackner ◽  
Amelie Mayer ◽  
Oliver Eppers ◽  
...  
Keyword(s):  
High Speed ◽  
Active Sites ◽  
Cloud Model ◽  
Temperature Shift ◽  
Freezing Temperature ◽  
Biological Species ◽  
Temperature Correction ◽  
Single Droplet ◽  
Cooling Rates ◽  
Immersion Freezing

Abstract. Immersion freezing experiments were performed utilizing two distinct single-droplet levitation methods. In the Mainz vertical wind tunnel (M-WT) supercooled droplets of 700 μm diameter were freely floated in a vertical air stream at constant temperatures ranging from −5 °C to −30 °C where heterogeneous freezing takes place. These investigations under isothermal conditions allow applying the stochastic approach to analyze and interpret the results in terms of the freezing or nucleation rate. In the Mainz acoustic levitator (M-AL) 2 mm diameter drops were levitated while their temperature was continuously cooling from +20 °C to −28 °C by adapting to the ambient temperature. Therefore, in this case the singular approach was used for analysis. From the experiments, the densities of ice nucleating active sites (INAS) were obtained as function of temperature. The direct comparison of the results from two different instruments indicates a shift of the freezing temperatures towards lower values that was material dependent. As ice nucleating particles, seven materials were investigated, two representatives of biological species (fibrous and microcrystalline cellulose), four mineral dusts (feldspar, illite NX, montmorillonite, and kaolinite), and natural Sahara dust. Based on detailed analysis of our results we determined a material dependent temperature correction factor for each investigated particle type. The analysis allowed further classifying the investigated materials as single- or multiple-component. From our experiences during the present synergetic studies, we listed a number of suggestions for future experiments regarding cooling rates, determination of the drop temperature, purity of the water used to produce the drops, and characterization of the ice nucleating material. The observed freezing temperature shift is significantly important not only for the intercomparison of ice nucleation instruments with different cooling rates but also for cloud model simulations with high speed ascents of air masses.

scholarly journals Enhanced ice nucleation efficiency of microcline immersed in dilute NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup>-containing solutions

2018 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Beiping Luo ◽  
Thomas Peter
Keyword(s):  
Volume Fraction ◽  
Pure Water ◽  
Freezing Temperature ◽  
Ice Nucleation ◽  
Ice Melting ◽  
Salt Solutions ◽  
Point Curve ◽  
Mineral Dusts ◽  
Immersion Freezing ◽  
Mixed Phase Clouds

Abstract. Potassium containing feldspars (K-feldspars) have been considered key mineral dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the effect of solutes on their IN efficiency, we performed immersion freezing experiments with the K-feldspar microcline, which is highly IN active. Freezing of emulsified droplets with microcline suspended in aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, NH4NO3, NH4Cl, Na2SO4, H2SO4, K2SO4 and KCl, with solute concentrations corresponding to water activities aw = 0.9–1.0, were investigated by means of a differential scanning calorimeter (DSC). The measured heterogeneous ice nucleation onset temperatures, Thet (aw) deviate strongly from Thet∆awhet (aw), the values calculated from the water-activity-based approach (where Thet∆awhet (aw) = Tmelt (aw + ∆awhet) with a constant offset ∆awhet with respect to the ice melting point curve). Surprisingly, for very dilute solutions of NH3 and NH4+-salts (molalities  ~ 0.96), we find IN temperatures raised by up to 4.5 K above the onset freezing temperature of microcline in pure water (Thet (aw = 1)) and 5.5 K above Thet∆awhet (aw), revealing NH3 and NH4+ to significantly enhance the IN of the microcline surface. Conversely, more concentrated NH3 and NH4+ solutions show a depression of the onset temperature below Thet∆awhet (aw) by as much as 13.5 K caused by a decline in IN ability accompanied with a reduction in the volume fraction of water frozen heterogeneously. All salt solutions not containing NH4+ as cation exhibit nucleation temperatures Thet (aw)  ~ 0.96) at warm (252–257 K) and NH3/NH4+-rich conditions.

scholarly journals Online Ice-Nucleating Particle Measurements in the Southern Great Plains (SGP) Using the Portable Ice Nucleation Experiment (PINE) Chamber

2020 ◽  
Vol 4 (1) ◽  
pp. 25
Author(s):  
Hemanth S. K. Vepuri ◽  
Larissa Lacher ◽  
Jens Nadolny ◽  
Ottmar Möhler ◽  
Naruki Hiranuma
Keyword(s):  
Great Plains ◽  
Cloud Condensation Nuclei ◽  
Active Surface ◽  
Freezing Temperature ◽  
Statistical Correlation ◽  
Ice Nucleation ◽  
High Time Resolution ◽  
Field Campaign ◽  
Southern Great Plains ◽  
Immersion Freezing

We present our field results of ice-nucleating particle (INP) measurements from the commercialized version of the Portable Ice Nucleation Experiment (PINE) chamber from two different campaigns. Our first field campaign, TxTEST, was conducted at West Texas A&M University (July–August 2019), and the other campaign, ExINP-SGP, was held at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site (October–November 2019). In both campaigns, the PINE made semi-autonomous INP measurements at a high-time-resolution of 8 min for individual expansions with continuous temperature scans from −5 to −35 °C in 90 min. The PINE instrument was set to have a minimum detection capability of ~0.3 INPs per liter of air. To complement our online PINE measurements, polycarbonate filter impactor and liquid impinger samples were also collected next to the PINE. Offline droplet-freezing assays were later conducted from the filter and impinger samples for the immersion freezing mode. Our preliminary results suggested that the immersion freezing mode was the dominant ice-nucleation mechanism at the SGP site compared to the deposition mode. We did not find any statistical correlation between cloud condensation nuclei (CCN) and INP concentration during our ExINP-SGP period, suggesting that CCN activation is not a significant prerequisite for ice nucleation at the SGP site. In addition, we analyzed the relationship between various aerosol particle size ranges and INP abundance. At SGP, we found an increase in INPs with the super-micron particles, especially for diameters >2 μm across the entire heterogeneous freezing temperature range examined by PINE. Lastly, we computed a variety of INP parameters, such as, ice nucleation active surface site density, water activity-based freezing, and cumulative INP per liter of air, representing the ambient INPs in the SGP. Our field campaign results demonstrated the PINE’s ability to make remote INP measurements, promising future long-term operations including at isolated locations.

scholarly journals Comparative study on immersion freezing utilizing single-droplet levitation methods

2021 ◽  
Vol 21 (5) ◽  
pp. 3289-3316
Author(s):  
Miklós Szakáll ◽  
Michael Debertshäuser ◽  
Christian Philipp Lackner ◽  
Amelie Mayer ◽  
Oliver Eppers ◽  
...  
Keyword(s):  
Active Sites ◽  
Temperature Shift ◽  
Freezing Temperature ◽  
Stochastic Approach ◽  
Ice Nucleation ◽  
Biological Species ◽  
Single Droplet ◽  
Cooling Rates ◽  
Immersion Freezing ◽  
Comparison Of The Results

Abstract. Immersion freezing experiments were performed utilizing two distinct single-droplet levitation methods. In the Mainz vertical wind tunnel, supercooled droplets of 700 µm diameter were freely floated in a vertical airstream at constant temperatures ranging from −5 to −30 ∘C, where heterogeneous freezing takes place. These investigations under isothermal conditions allow the application of the stochastic approach to analyze and interpret the results in terms of the freezing or nucleation rate. In the Mainz acoustic levitator, 2 mm diameter drops were levitated while their temperature was continuously cooling from +20 to −28 ∘C by adapting to the ambient temperature. Therefore, in this case the singular approach was used for analysis. From the experiments, the densities of ice nucleation active sites were obtained as a function of temperature. The direct comparison of the results from two different instruments indicates a shift in the mean freezing temperatures of the investigated drops towards lower values that was material-dependent. As ice-nucleating particles, seven materials were investigated; two representatives of biological species (fibrous and microcrystalline cellulose), four mineral dusts (feldspar, illite NX, montmorillonite, and kaolinite), and natural Sahara dust. Based on detailed analysis of our results we determined a material-dependent parameter for calculating the freezing-temperature shift due to a change in cooling rate for each investigated particle type. The analysis allowed further classification of the investigated materials to be described by a single- or a multiple-component approach. From our experiences during the present synergetic studies, we listed a number of suggestions for future experiments regarding cooling rates, determination of the drop temperature, purity of the water used to produce the drops, and characterization of the ice-nucleating material. The observed freezing-temperature shift is significantly important for the intercomparison of ice nucleation instruments with different cooling rates.

The ice nucleating ability of macromolecules in immersion freezing decreases in the presence of salts: Implications for freezing point depression calculations

2021 ◽  
Author(s):  
Jon F. Went ◽  
Jeanette D. Wheeler ◽  
François J. Peaudecerf ◽  
Nadine Borduas-Dedekind
Keyword(s):  
Sea Water ◽  
Freezing Point ◽  
Pure Water ◽  
Salt Content ◽  
Mixed Phase ◽  
Cloud Formation ◽  
Sea Spray ◽  
Freezing Point Depression ◽  
Immersion Freezing ◽  
Mixed Phase Clouds

&lt;p&gt;Cloud formation represents a large uncertainty in current climate predictions. In particular, ice in mixed-phase clouds requires the presence of ice nucleating particles (INPs) or ice nucleating macromolecules (INMs). An influential population of INPs has been proposed to be organic sea spray aerosols in otherwise pristine ocean air. However, the interactions between INMs present in sea water and their freezing behavior under atmospheric immersion freezing conditions warrants further research to constrain the role of sea spray aerosols on cloud formation. Indeed, salt is known to lower the freezing temperature of water, through a process called freezing point depression (FPD). Yet, current FPD corrections are solely based on the salt content and assume that the INMs&amp;#8217; ice nucleation abilities are identical with and without salt. Thus, we measured the effect of salt content on the ice nucleating ability of INMs, known to be associated with marine phytoplankton, in immersion freezing experiments in the Freezing Ice Nuclei Counter (FINC) (Miller et al., AMTD, 2020). We measured eight INMs, namely taurine, isethionate, xylose, mannitol, dextran, laminarin, and xanthan as INMs in pure water at temperatures relevant for mixed-phase clouds (e.g. 50% activated fraction at temperatures above &amp;#8211;23 &amp;#176;C at 10 mM concentration). Subsequently, INMs were analyzed in artificial sea water containing 36 g salt L&lt;sup&gt;-1&lt;/sup&gt;. Most INMs, except laminarin and xanthan, showed a loss of ice activity in artificial sea water compared to pure water, even after FPD correction. Based on our results, we hypothesize sea salt has an inhibitory effect on the ice activity of INMs. This effect influences our understanding of how INMs nucleate ice as well as challenges our use of FPD correction and subsequent extrapolation to ice activity under mixed-phase cloud conditions.&lt;/p&gt;

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 Aerosol–Ice Formation Closure: A Southern Great Plains Field Campaign

2021 ◽  
pp. 1-50
Author(s):  
D. A. Knopf ◽  
K. R. Barry ◽  
T. A. Brubaker ◽  
L. G. Jahl ◽  
K. A., L. Jankowski ◽  
...  
Keyword(s):  
Pilot Study ◽  
Great Plains ◽  
Climate Models ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Ice Formation ◽  
Crystal Formation ◽  
Atmospheric Sciences ◽  
Immersion Freezing ◽  
Mixed Phase Clouds

AbstractPrediction of ice formation in clouds presents one of the grand challenges in the atmospheric sciences. Immersion freezing initiated by ice-nucleating particles (INPs) is the dominant pathway of primary ice crystal formation in mixed-phase clouds, where supercooled water droplets and ice crystals coexist, with important implications for the hydrological cycle and climate. However, derivation of INP number concentrations from an ambient aerosol population in cloud-resolving and climate models remains highly uncertain. We conducted an aerosol-ice formation closure pilot study using a field-observational approach to evaluate the predictive capability of immersion freezing INPs. The closure study relies on co-located measurements of the ambient size-resolved and single-particle composition and INP number concentrations. The acquired particle data serve as input in several immersion freezing parameterizations, that are employed in cloud-resolving and climate models, for prediction of INP number concentrations. We discuss in detail one closure case study in which a front passed through the measurement site, resulting in a change of ambient particle and INP populations. We achieved closure in some circumstances within uncertainties, but we emphasize the need for freezing parameterization of potentially missing INP types and evaluation of the choice of parameterization to be employed. Overall, this closure pilot study aims to assess the level of parameter details and measurement strategies needed to achieve aerosol-ice formation closure. The closure approach is designed to accurately guide immersion freezing schemes in models, and ultimately identify the leading causes for climate model bias in INP predictions.

scholarly journals Cleaning up our water: reducing interferences from nonhomogeneous freezing of “pure” water in droplet freezing assays of ice-nucleating particles

2018 ◽  
Vol 11 (9) ◽  
pp. 5315-5334 ◽  
Author(s):  
Michael Polen ◽  
Thomas Brubaker ◽  
Joshua Somers ◽  
Ryan C. Sullivan
Keyword(s):  
Pure Water ◽  
Freezing Temperature ◽  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Great Promise ◽  
Water Control ◽  
Temperature Spectra ◽  
Droplet Sizes ◽  
Mixed Phase Clouds ◽  
Insight Into

Abstract. Droplet freezing techniques (DFTs) have been used for half a century to measure the concentration of ice-nucleating particles (INPs) in the atmosphere and determine their freezing properties to understand the effects of INPs on mixed-phase clouds. The ice nucleation community has recently adopted droplet freezing assays as a commonplace experimental approach. These droplet freezing experiments are often limited by contamination that causes nonhomogeneous freezing of the “pure” water used to generate the droplets in the heterogeneous freezing temperature regime that is being measured. Interference from the early freezing of water is often overlooked and not fully reported, or measurements are restricted to analyzing the more ice-active INPs that freeze well above the temperature of the background water. However, this avoidance is not viable for analyzing the freezing behavior of less active INPs in the atmosphere that still have potentially important effects on cold-cloud microphysics. In this work we review a number of recent droplet freezing techniques that show great promise in reducing these interferences, and we report our own extensive series of measurements using similar methodologies. By characterizing the performance of different substrates on which the droplets are placed and of different pure water generation techniques, we recommend best practices to reduce these interferences. We tested different substrates, water sources, droplet matrixes, and droplet sizes to provide deeper insight into what methodologies are best suited for DFTs. Approaches for analyzing droplet freezing temperature spectra and accounting and correcting for the background “pure” water control spectrum are also presented. Finally, we propose experimental and data analysis procedures for future homogeneous and heterogeneous ice nucleation studies to promote a more uniform and reliable methodology that facilitates the ready intercomparison of ice-nucleating particles measured by DFTs.

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