Journal Article
Atmospheric Measurement Techniques, vol. 13, iss. 12, pp. 6631-6643, 2020
Authors
Gourihar Kulkarni, Naruki Hiranuma, Ottmar Möhler, Kristina Höhler, Swarup China, Daniel J. Cziczo, Paul J. DeMott
Abstract
Abstract. 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 −20 ∘C and water relative humidity (RHw) 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 ∘C min−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 (ns) metric were higher but mostly agreed within 1 order of magnitude compared to results reported in the literature.
