A new method for operating a continuous-flow diffusion chamber to investigate immersion freezing: assessment and performance study

• Main Authors: G. Kulkarni, N. Hiranuma, O. Möhler, K. Höhler, S. China, D. J. Cziczo, P. J. DeMott
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-12-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://amt.copernicus.org/articles/13/6631/2020/amt-13-6631-2020.pdf

<p>Glaciation in mixed-phase clouds predominantly occurs through the immersion-freezing mode where ice-nucleating particles (INPs) immersed within supercooled droplets induce the nucleation of ice. Model representations of this process currently are a large source of uncertainty in simulating cloud radiative properties, so to constrain these estimates, continuous-flow diffusion chamber (CFDC)-style INP devices are commonly used to assess the immersion-freezing efficiencies of INPs. This study explored a new approach to operating such an ice chamber that provides maximum activation of particles without droplet breakthrough and correction factor ambiguity to obtain high-quality INP measurements in a manner that previously had not been demonstrated to be possible. The conditioning section of the chamber was maintained at <span class="inline-formula">−</span>20&thinsp;<span class="inline-formula">^∘</span>C and water relative humidity (RH<span class="inline-formula">_w</span>) conditions of 113&thinsp;% to maximize the droplet activation, and the droplets were supercooled with an independently temperature-controlled nucleation section at a steady cooling rate (0.5&thinsp;<span class="inline-formula">^∘</span>C&thinsp;min<span class="inline-formula">⁻¹</span>) to induce the freezing of droplets and evaporation of unfrozen droplets. The performance of the modified compact ice chamber (MCIC) was evaluated using four INP species: K-feldspar, illite-NX, Argentinian soil dust, and airborne soil dusts from an arable region that had shown ice nucleation over a wide span of supercooled temperatures. Dry-dispersed and size-selected K-feldspar particles were generated in the laboratory. Illite-NX and soil dust particles were sampled during the second phase of the Fifth International Ice Nucleation Workshop (FIN-02) campaign, and airborne soil dust particles were sampled from an ambient aerosol inlet. The measured ice nucleation efficiencies of model aerosols that had a surface active site density (<span class="inline-formula"><i>n</i>_s</span>) metric were higher but mostly agreed within 1 order of magnitude compared to results reported in the literature.</p>