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Enhanced high‐temperature ice nucleation ability of crystallized aerosol particles after preactivation at low temperature
Author(s) -
Wagner Robert,
Möhler Ottmar,
Saathoff Harald,
Schnaiter Martin
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd021741
Subject(s) - ice nucleus , nucleation , aerosol , crystallization , ice crystals , aqueous solution , chemical engineering , eutectic system , particle (ecology) , supercooling , ammonium sulfate , clear ice , chemistry , materials science , chemical physics , mineralogy , thermodynamics , crystallography , chromatography , meteorology , geology , microstructure , organic chemistry , arctic ice pack , sea ice , physics , oceanography , antarctic sea ice , engineering
In cloud chamber experiments with crystallized aqueous ammonium sulfate, oxalic acid, and succinic acid solution droplets, we have studied a preactivation mechanism that markedly enhances the particles' heterogeneous ice nucleation ability. First cloud expansion experiments were performed at a high temperature (267–244 K) where the crystallized particles did not promote any heterogeneous ice nucleation. Ice nucleation at this temperature, however, could be triggered by temporarily cooling the crystallized particles to a lower temperature. This is because upon crystallization, residuals of the aqueous solution are trapped within the crystals. These captured liquids can freeze when cooled below their respective homogeneous or heterogeneous freezing temperature, leading to the formation of ice pockets in the crystalline particles. When warmed again to the higher temperature, ice formation by the preactivated particles occurred via depositional and deliquescence‐induced ice growth, with ice active fractions ranging from 1 to 4% and from 4 to 20%, respectively. Preactivation disappeared above the eutectic temperature, which for the organic acids are close to the melting point of ice. This mechanism could therefore contribute to the very small fraction of atmospheric aerosol particles that are still ice active well above 263 K.