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

Kulkarni, Gourihar; Hiranuma, Naruki; Möhler, Ottmar; Höhler, Kristina; China, Swarup; Cziczo, Daniel J.; DeMott, Paul J.

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 inline-formula−20 inline-formulaC and water relative humidity (RHinline-formulaw) conditions of 113 % to maximize the droplet activation, and the droplets were supercooled with an independently temperature-controlled nucleation section at a steady cooling rate (0.5 inline-formulaC mininline-formula−1) 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 (inline-formulans) metric were higher but mostly agreed within 1 order of magnitude compared to results reported in the literature.

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Kulkarni, Gourihar / Hiranuma, Naruki / Möhler, Ottmar / et al: A new method for operating a continuous-flow diffusion chamber to investigate immersion freezing: assessment and performance study. 2020. Copernicus Publications.

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Rechteinhaber: Gourihar Kulkarni et al.

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