Abstract
Abstract. For efficient analysis and characterization of biological ice nuclei under immersion freezing conditions, we developed the Twin-plate Ice Nucleation Assay (TINA) for high-throughput droplet freezing experiments, in which the temperature profile and freezing of each droplet is tracked by an infrared detector. In the fully automated setup, a couple of independently cooled aluminum blocks carrying two 96-well plates and two 384-well plates, respectively, are available to study ice nucleation and freezing events simultaneously in hundreds of microliter-range droplets (0.1–40 µL). A cooling system with two refrigerant circulation loops is used for high-precision temperature control (uncertainty <0.2 K), enabling measurements over a wide range of temperatures (∼ 272–233 K) at variable cooling rates (up to 10 K min−1). The TINA instrument was tested and characterized in experiments with bacterial and fungal ice nuclei (IN) from Pseudomonas syringae (Snomax®) and Mortierella alpina, exhibiting freezing curves in good agreement with literature data. Moreover, TINA was applied to investigate the influence of chemical processing on the activity of biological IN, in particular the effects of oxidation and nitration reactions. Upon exposure of Snomax® to O3 and NO2, the cumulative number of IN active at 270–266 K decreased by more than 1 order of magnitude. Furthermore, TINA was used to study aqueous extracts of atmospheric aerosols, simultaneously investigating a multitude of samples that were pre-treated in different ways to distinguish different kinds of IN. For example, heat treatment and filtration indicated that most biological IN were larger than 5 µm. The results confirm that TINA is suitable for high-throughput experiments and efficient analysis of biological IN in laboratory and field samples.
Highlights
Clouds and aerosols still contribute the largest uncertainty to the evaluation of the Earth’s changing energy budget (Boucher et al, 2013)
Twin-plate Ice Nucleation Assay (TINA) provides the analysis of 960 droplets simultaneously or 192 and 768 droplets in two independent experiments at the same time, enabling the analysis of many samples with high statistics in a short period of time
An infrared camerabased detection system allows the reliable determination of droplet freezing
Summary
Clouds and aerosols still contribute the largest uncertainty to the evaluation of the Earth’s changing energy budget (Boucher et al, 2013). IR video thermography has been used in a range of studies investigating freezing in plants (e.g., Ball et al, 2002; Carter et al, 1999; Charrier et al, 2017; Fuller and Wisniewski, 1998; Hacker and Neuner, 2007; Pearce and Fuller, 2001; Sekozawa et al, 2004; Stier et al, 2003; Wisniewski et al, 2008; Workmaster, 1999). Further applications of IR video thermography are investigations of cold thermal stress in insects (Gallego et al, 2016), monitoring of freeze-drying processes (Emteborg et al, 2014), as well as detection of ice in wind turbine blades (Gómez Muñoz et al, 2016) and helicopter rotor blades (Hansman and Dershowitz, 1994).
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