Homogeneous ice nucleation observed in single levitated micro droplets

Abstract

Homogeneous ice nucleation rates in single isolated micro droplets of water are determined under various atmospheric conditions inside an electrodynamic Paul-trap. The droplet size is measured by angle-resolved detection of the scattered light from a Helium-Neon laser. The freezing process is detected by a sudden change of the depolarization ratio which is an indication for the formation of nonspherical particles.The experimentally determined homogeneous ice nucleation rates JLs are JLs = ( 2 . 2~0 0 . 4 ) . 1 0 8 c m~3 s -' at T = (-37.2kO.15)'C and JLs = (5.6e 1.0). 10' c r K 3 sat T = ( -37.7 * 0.15)OC.These values are much more precise as determined by measurements inside a cloud expansion chamber. The method of single particle observation eliminates complications arising from these nucleation rate measurements. The results underline the theory that one single ice germ of certain size is sufficient to induce the freezing of the whole droplet. The depolarization ratio of the scattered intensity in the parallel and perpendicular polarization plane I, / I p from the frozen particles exhibits a broad distribution with a mean value of Zs(Ip = 0.3.

An Electrodynamic Levitation System for Studying Individual Cloud Particles under Upper-Tropospheric Conditions

“…For typical droplet sizes suspended in this system, this charge is roughly two orders of magnitude below the Rayleigh limit (Pruppacher and Klett, p. 806). While it is important to keep possible limitations in mind, it appears that there is no observable charge-influence on the processes of evaporation (Tang and Munkelwitz 1991), homogeneous freezing nucleation (Krämer et al 1996;Shaw and Lamb 1999a), uptake of trace gases, or deliquescence (Lamb et al 1996). We will show both evaporation and ho- mogeneous freezing nucleation measurements made in our system that are consistent with other measurements made with different techniques, confirming that electrodynamic levitation is a valuable tool for many atmospheric problems.…”

Laboratory evidence for volume-dominated nucleation of ice in supercooled water microdroplets

“…Rates for the homogeneous freezing of water ice have been measured previously in laboratory experiments by Taborek (1985) using emulsion samples, by DeMott and Rogers (1990) in cloud chambers, by Wood et al (2002) in droplet trains and in levitated single particles by Krämer et al (1996Krämer et al ( , 1999 and Stöckel et al (2002). The droplets in these experiments were between 3 µm and 300 µm in diameter and in all cases the data were interpreted as volume-nucleation rates, Correspondence to: Thomas Leisner (thomas.leisner@tu-ilmenau.de) i.e.…”

Single ice crystal measurements during nucleation experiments with the depolarization detector IODE

“…Several experimental applications have been built for single particle detection such as the Small Ice detector (SID) (Hirst et al, 2001), the Particle Measurement System forward scattering probe (FSSP) (Lawson and Cormack, 1995) and the Video Ice Particle Sampler (VIPS) (McFarquhar et al, 2002). Other optical systems dealt with ice nucleation of single levitated (Krämer et al, 1996) or free-falling droplets (Wood et al, 2002) where detection of ice particles using depolarization has been performed. The influence of the particle orientation on the depolarization ratio is large, according to a previous modeling study (Nicolet et al, 2007).…”