Abstract
AbstractIn this study we present results from immersion freezing experiments with size‐segregated mineral dust particles. Besides two already existing data sets for Arizona Test Dust (ATD), and Fluka kaolinite, we show two new data sets for illite‐NX, which consists mainly of illite, a clay mineral, and feldspar, a common crustal material. The experiments were carried out with the Leipzig Aerosol Cloud Interaction Simulator. After comparing the different dust samples, it became obvious that the freezing ability was positively correlated with the K‐feldspar content. Furthermore, a comparison of the composition of the ATD, illite‐NX, and feldspar samples suggests that within the K‐feldspars, microcline is more ice nucleation active than orthoclase. A coating with sulfuric acid leads to a decrease in the ice nucleation ability of all mineral dusts, with the effect being more pronounced for the feldspar sample.
Highlights
Ice particles influence both the cloud radiative properties and the cloud lifetime [Storelvmo et al, 2011; Lohmann and Diehl, 2006]
In this study we present results from immersion freezing experiments with size-segregated mineral dust particles
A coating with sulfuric acid leads to a decrease in the ice nucleation ability of all mineral dusts, with the effect being more pronounced for the feldspar sample
Summary
Ice particles influence both the cloud radiative properties and the cloud lifetime [Storelvmo et al, 2011; Lohmann and Diehl, 2006]. There are two primary processes that can initiate ice nucleation in the atmosphere, homogeneous and heterogeneous ice nucleation [Pruppacher and Klett, 1997]. In contrast to the homogeneous ice nucleation, the heterogeneous ice nucleation is induced by a so-called ice nucleating particle (INP). This INP lowers the energy barrier for the phase transition from water to ice, causing ice nucleation at higher temperatures than observed for homogeneous ice nucleation (−38◦C), for which no INP is present. Four different modes of heterogeneous ice nucleation are mentioned in the literature: deposition nucleation, immersion freezing, condensation freezing, and contact freezing [Pruppacher and Klett, 1997]. Four different modes of heterogeneous ice nucleation are mentioned in the literature: deposition nucleation, immersion freezing, condensation freezing, and contact freezing [Pruppacher and Klett, 1997]. Ansmann et al [2009] suggested the immersion freezing mode to be the most important freezing mode in mixed phase clouds, as they observed altocumulus clouds to almost always show a liquid cloud top before an onset of freezing was observed
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