Heterogeneous Freezing of Liquid Suspensions Including Juices and Extracts from Berries and Leaves from Perennial Plants

Laura Felgitsch,Thomas Häusler,Bianca Fiala,Magdalena Bichler,Julia Burkart,Hinrich Grothe,Regina Hitzenberger

doi:10.3390/atmos10010037

Abstract

Heterogeneous ice nucleation in the atmosphere is not fully understood. In particular, our knowledge of biological materials and their atmospheric ice nucleation properties remains scarce. Here, we present the results from systematic investigations of the ice nucleation activity of plant materials using cryo-microscopy. We examined berry juices, frozen berries, as well as extracts of leaves and dried berries of plants native to boreal regions. All of our samples possess reasonable ice nucleation activity. Their ice nucleating particle concentrations per unit of water volume vary between 9.7 × 105 and 9.2 × 109 cm−3 when examined within temperatures of −12 to −34 °C. Mean freezing temperatures ranged from −18.5 to −45.6 °C. We show that all samples contained ice nuclei in a size range below 0.2 µm and remain active if separated from coarse plant tissue. The results of examining ice nucleation properties of leaves and dry berry extracts suggests that their ice-nucleating components can be easily suspended in water. Sea buckthorn and black currant were analyzed using subtilisin (a protease) and urea. Results suggest proteinaceous compounds to play an important role in their ice nucleation activity. These results show that separation between ice nucleation particles stemming from microorganisms and those stemming from plants cannot be differentiated solely on proteinaceous features. Further oxidation experiments with ozone showed that black currant is highly stable towards ozone oxidation, indicating a long atmospheric life time.

Highlights

While ice is the thermodynamically favorable phase at temperatures below 0 ◦ C, ice formation is a kinetically hindered process and will typically not take place at higher sub-zero temperatures [1,2,3].For small volumes this transition occurs at temperatures below −35 ◦ C [4,5]
We found no significant change in the freezing temperature in the 12 h of treatment, indicating that the ice nucleation activity (INA) of black currant juice is not affected by ozone
Since the transport mechanisms of biological materials into the atmosphere are not well corroborated, more detailed studies of plant based ice nucleating particles (INP) are of great importance

Summary

Introduction

While ice is the thermodynamically favorable phase at temperatures below 0 ◦ C, ice formation is a kinetically hindered process and will typically not take place at higher sub-zero temperatures [1,2,3].For small volumes (as droplets in the lower μm size range) this transition occurs at temperatures below −35 ◦ C [4,5]. While ice is the thermodynamically favorable phase at temperatures below 0 ◦ C, ice formation is a kinetically hindered process and will typically not take place at higher sub-zero temperatures [1,2,3]. If ice nucleation active substances, called ice nucleating particles (INP) [6], initiate freezing at higher (sub-zero) temperatures, the process is referred to as heterogeneous ice nucleation. Within the large field of INP, biological INP, which often exhibit the highest onset temperatures (near 0 ◦ C) are least understood [11,12,13]. It is generally assumed that larger particles and especially mineral dust are mainly responsible for atmospheric heterogeneous ice nucleation events [14,15]. Possible atmospheric impacts of biological particles have been studied

Objectives

Methods

Results

Discussion

Conclusion