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

Abstract

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.

Development of the DRoplet Ice Nuclei Counter Zurich (DRINCZ): validation and application to field-collected snow samples

“…This result shows that by using the spatially dependent freezing information of a well from optically based drop-freezing instruments like DRINCZ, temperature can be better constrained. Such a bias correction should also be applicable to freezing methods that use block-based cooling, where gradients across the block have been observed or modeled (Beall et al, 2017;Harrison et al, 2018).…”

“…Singleparticle methods, such as continuous-flow diffusion chambers (Rogers, 1988;Stetzer et al, 2008) operated at water supersaturated conditions (DeMott et al, 2015(DeMott et al, , 2017Hiranuma et al, 2015), or with extended chambers that activate individual particles into cloud droplets before exposing them to supercooled conditions (Burkert- Kohn et al, 2016;Lüönd et al, 2010), allow for the quantification of the number concentration of INPs as a function temperature. Larger laboratory-based single-particle methods for examining INPs in the immersion mode include expansion chambers where cloud droplets are first formed by adiabatic cooling due to the expansion of an air volume (Niemand et al, 2012) or experiments where droplets are initially activated and then subsequently cooled as they travel through a laminar flow tube (Hartmann et al, 2011). Aerosols introduced into such systems by dry dispersion or atomization of suspensions and solutions allow for a range of particulates to be examined.…”

“…However, in some cases dilution alone cannot be used to observe the total number of INP (T ) values due to the presence of impurities that act as INPs in the water used for dilution (Polen et al, 2018). Therefore, it is necessary to use different bulk techniques that measure aliquots with volumes that span several orders of magnitude, typically microliter to picoliter volumes (Harrison et al, 2018;Hill et al, 2014;Murray et al, 2010;Whale et al, 2015).…”

Size-dependent ice nucleation by airborne particles during dust events in the eastern Mediterranean

“…Cloud droplets can supercool to 238 K before homogeneous freezing occurs (Koop and Murray, 2016;Rosenfeld and Woodley, 2000). At warmer temperatures, heterogeneous ice nucleation (HIN), whereby the presence of aerosol particles lowers the required energy barrier to form a stable ice nucleus, is the common pathway of ice formation Pruppacher and Klett, 1997;Khvorostyanov and Curry, 2004;Hoose and Möhler, 2012). These ice-nucleating particles (INPs) can be activated at subzero temperatures and subsequently lower humidity conditions, mainly by interaction with supercooled droplets.…”

Review of Kassmannhuber et al. 2019

“…e.g. Häusler et al 2018or Harrison et al 2018. I also miss the cooling rates of the experiments, which has an important impact on the results.…”