Particle-area dependence of mineral dust in the immersion mode: investigations with freely suspended drops in an acoustic levitator

Abstract

Abstract. The heterogeneous freezing temperatures of supercooled drops were measured by using an acoustic levitator. This technique allows to freely suspending single drops in air without electrical charges thereby avoiding any electrical influences which may affect the freezing process. Heterogeneous nucleation caused by several mineral dust particles (montmorillonite, two types of illite) was investigated in the immersion mode. Drops of 1 \\unit{mm} in radius were monitored by a~video camera during cooling down to −28 °C to simulate the tropospheric temperature range. The surface temperature of the drops was remotely determined with an infra-red thermometer so that the onset of freezing was indicated. For comparisons, measurements with one particle type were additionally performed in the Mainz vertical wind tunnel with drops of 340 \\unit{{\\mu}m} radius freely suspended. The data were interpreted regarding the particle surfaces immersed in the drops. Immersion freezing was observed in a~temperature range between −13 and −26 °C in dependence of particle type and surface area per drop. The results were evaluated by applying two descriptions of heterogeneous freezing, the stochastic and the singular model.

A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of seventeen ice nucleation measurement techniques

“…The freezing temperature of INPs either immersed in or in contact with levitated 25 supercooled water droplets suspended in the air can also be determined by the change in light scattering with a charge-coupled device (CCD) camera using an electrodynamic balance (EDB; Hoffmann et al, 2013), an acoustic levitator (Diehl et al, 2014) or in a vertical wind tunnel (Szakáll et al, 2009). The advantage of these methods is the Figures Back Close…”