Experimental study on the ice nucleation ability of size‐selected kaolinite particles in the immersion mode

Abstract

[1] The recently developed immersion mode cooling chamber has been used as an extension of the Zurich ice nucleation chamber (ZINC) in order to measure the ice nucleation efficiency of size-selected kaolinite particles in the immersion mode. Particles with selected diameters of 200, 400, and 800 nm have been activated as cloud condensation nuclei in order to obtain water droplets with single immersed particles. After continuous cooling of the droplets to the experimental temperature in ZINC, the frozen fraction of the droplets was measured with a recently developed depolarization detector, the ice optical detector (IODE). Temperatures below −30°C were necessary to freeze 50% of the droplets throughout the investigated size range. Although not very strong, a size dependence of the freezing efficiency has been observed. The median freezing temperature increases from −35°C for 200 nm kaolinite particles to −33°C for 800 nm particles. An experiment with 200 nm ammonium sulfate particles in the same temperature range resulted in no significant frozen fraction of the droplets. This suggests that the ice crystals observed in experiments with kaolinite particles nucleated heterogeneously. The temperature-dependent frozen fraction of water droplets has been fitted with different theoretical models. Comparison of the resulting fit curves with the data suggests that including the concept of active sites in the description of the ice nucleus surface is more appropriate than the approximation of a constant contact angle.Citation: Lüönd, F., O. Stetzer, A. Welti, and U. Lohmann (2010), Experimental study on the ice nucleation ability of size-selected kaolinite particles in the immersion mode,

Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory

“…However, in polydisperse samples, the surface area of INPs present in a droplet can vary from droplet to droplet even if the mass is the same because a few small particles have a larger total surface area than a single large one (Alpert and Knopf, 2016), leading to an additional variability of freezing rates when the ice nucleation site density scales with surface area (Hartmann et al, 2016). In investigations with continuous-flow diffusion chambers (Welti et al, 2012;Lüönd et al, 2010), many particles are investigated individually and a less steep temperature dependence of heterogeneous nucleation rates compared with the homogeneous case is observed. However, there is strong evidence that the surfaces of most ice-nucleating particles are not uniform with respect to their ability to nucleate ice (e.g., Marcolli et al, 2007;Vali, 2014).…”

A physically constrained classical description of the homogeneous nucleation of ice in water

“…Each J hom data set was weighted equally by representing it with three data points, at the maximum, minimum, and average temperature, determined from a straight line fit to ln(J hom ) versus T. In addition, we grouped measurements from separate papers, but made with the same instrument and methodology, into single data sets (i.e., we grouped data from Duft and Leisner 58 with Rzesanke et al, 59 Stöckel et al 61 with Kabath et al, 62 as well as Hoyle et al 64 with Lüönd et al 65 ). The resulting CNT fits are shown in Figure 3, with different lines originating from employing different parameterizations of D(T).…”

“…1,56 In this study, we have selected a subset [56][57][58][59][60][61][62][63][64][65][66][67][68] of the available data sets for the purposes of constraining the new parameterization. The criteria for selection were (i) minimal and well defined uncertainties, (ii) good reproducibility within the data set, and (iii) an internal droplet pressure of about 1 bar.…”

A new temperature- and humidity-dependent surface site density approach for deposition ice nucleation

“…Several studies have pointed out that often a single contact angle is not sufficient to characterize the ice nucleation behavior of a non-homogeneous aerosol population (Marcolli et al, 2007;Lüönd et al, 2010;Wheeler and Bertram, 2012;Broadley et al, 2012;Rigg et al, 2013). Thus, the nucleation I. Steinke et al: Describing deposition ice nucleation by an active site density approach 3705 rate approach was extended towards including not only a single contact angle but a distribution of contact angles (Marcolli et al, 2007;Lüönd et al, 2010). For this study, the distribution p(θ ) is assumed to be lognormal:…”

“…Lüönd et al (2010), Murray et al (2011), Wheeler and Bertram (2012), Broadley et al (2012) and Rigg et al (2013). Classical nucleation theory is based on the premise that the ice nucleation efficiency of aerosol particles can be quantified by the contact angle θ , which is a measure of the reduction of the energy barrier that impedes the formation of ice germs at the surface of aerosol particles (Pruppacher and Klett, 1997).…”