Immersion Freezing of Total Ambient Aerosols and Ice Residuals

Gourihar Kulkarni

doi:10.3390/atmos9020055

Abstract

This laboratory study evaluates an experimental set-up to study the immersion freezing properties of ice residuals (IRs) at a temperature ranging from −26 to −34 °C using two continuous-flow diffusion chamber-style ice nucleation chambers coupled with a virtual impactor and heat exchanger. Ice was nucleated on the total ambient aerosol through an immersion freezing mechanism in an ice nucleation chamber (chamber 1). The larger ice crystals formed in chamber 1 were separated and sublimated to obtain IRs, and the frozen fraction of these IRs was investigated in a second ice nucleation chamber (chamber 2). The ambient aerosol was sampled from a sampling site located in the Columbia Plateau region, WA, USA, which is subjected to frequent windblown dust events, and only particles less than 1.5 μm in diameter were investigated. Single-particle elemental composition analyses of the total ambient aerosols showed that the majority of the particles are dust particles coated with organic matter. This study demonstrated a capability to investigate the ice nucleation properties of IRs to better understand the nature of Ice Nucleating Particles (INPs) in the ambient atmosphere.

Highlights

Atmospheric Ice Nucleating Particles (INPs) can be airborne particles such as pollen, biological spores, bacteria, plant debris, inorganic dust, volcanic ash, organics, salts, meteoritic particles, and complex mixtures of organic and inorganic compounds [1,2]
The composition results revealed that minerals coated with organics dominated the total aerosol particle population (Figure 4)
This approach does not take into account the time dependence of the nucleation events but does describe the number of ice nucleation actives sites at a defined temperature and humidity conditions normalized by the particle surface area

Summary

Introduction

Atmospheric INPs can be airborne particles such as pollen, biological spores, bacteria, plant debris, inorganic dust, volcanic ash, organics, salts, meteoritic particles, and complex mixtures of organic and inorganic compounds [1,2]. Laboratory experiments have been conducted to investigate a wide range of potential INP sources [3,4,5,6,7,8,9,10,11,12,13,14,15] While these studies have improved our understanding of INP number concentration and freezing temperatures across the range of ice nucleation mechanisms significantly, it is often assumed in cloud models that the history of an individual particle does not influence its ice-nucleating properties [16,17,18,19,20]. It has been demonstrated that these IRs may further induce ice crystal formation through recycling and maintain cloud production [23]

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Conclusion