Eisnukleationsaktivität von borealen Pflanzen mit Fokus auf Birken

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersZwei Drittel der Erde sind mit Wolken bedeckt. Die Erde ist daher eher ein weißer Planet als ein Blauer. Wolken haben großen Einfluss auf die Albedo der Erde. Allerdings verhalten sich Wolken sehr unterschiedlich. Der Aggregatszustand des enthaltenen Wassers beeinflusst das Abregnen und die Wechselwirkung mit der ein- und ausfallenden Strahlung. Reines Wasser gefriert nicht beiTwo thirds of the Earth are covered by clouds, rendering our planet a white planet rather than a blue one. Hence, clouds have a huge impact on the albedo of the Earth; however, not every cloud acts in the same manner. The microphysical state of the water present in clouds affects precipitation and lifespan of a cloud, as well as their radiative properties. Pure water does not freeze at 0C (the thermodynamic freezing point of water), since freezing is a kinetically hindered process, but rather at far lower temperatures. Pure water droplets in the micrometre size range, such as cloud droplets, freeze only at temperatures around -36 C. Impurities can influence the freezing process by shifting the freezing event to higher temperatures. These are called ice nucleating particles and the process is referred to as heterogeneous nucleation. So far, ice nucleating particles have been found in almost all kingdoms of life, playing a part in the life of many different organisms for a wide range of functions. This work focusses on the ice nucleation activity of plants native to the boreal region. Boreal regions exhibit night frosts even during the warm seasons and winter temperatures that can be as cold as -40 C. However, even under these conditions, life has prevailed and found various mechanisms to cope with the cold. Several plants have developed mechanisms, allowing them to control freezing within their tissue. They exhibit many different molecules regulating not just temperature but also crystal size and cell stability. These properties make plants native to the boreal regions very interesting candidates for ice nucleation research. So far, very little is known about the ice nucleation activity of plants. In 2001, Diehl and colleagues showed that single birch pollen can act as efficient ice nucleating particles. More than ten years later, Pummer and colleagues (2012) published data showing that the size of the ice nucleating component is in the submicron size and that it can be easily washed off the pollen-surface. Due to its small size and its stability towards reactive oxygen species, it has the potential for a long atmospheric lifespan. The chemical nature of the ice nuclei extractable from birch pollen is not fully understood. One goal of this work is to further elucidate their composition. Different biochemical separation techniques (e.g. solid phase extraction cartridges) as well as vibrational spectroscopy were applied. Further, chaotropic reagents and enzymes are used to analyse the role of proteins in the process of heterogeneous ice nucleation. The examined plant material was collected from several parts of ten different birch trees. In this work it was shown that all analysed parts of birch trees (primary wood, secondary wood, leaves, bark, and drill cores of the stem) were ice nucleation active. The contained ice nucleating particles show strong similarities to those found in pollen. Different sample preparations and extractions allowed us to estimate not just the total contained concentration in the plant material, but also the amount of ice nuclei that is easily accessible for the surrounding environment of the tree. Apart from birch trees, berries from several perennial plants (black currant, blueberry, cranberry, chokeberry, lingonberry, sambucus, sea buckthorn, raspberry, and rowanberry) were investigated. Further leaves of blueberry, juniper, raspberry, and sea buckthorn were analysed. All samples were ice nucleation active, showing how far spread this ability is in the Boreal plant kingdom.19

Bestimmung der Oxidativen Eigenschaften von Feinstaubproben

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersOxidative properties of different particulate matter samples were analyzed using an approach based on oxidation of ascorbate. Therefore aliquots of the samples were incubated with a buffer solution imitating the RELF (respiratory extracellular lining fluid) containing ascorbic acid. The depletion of ascorbic acid was determined using reversed phase liquid chromatography and an UV detector. The measurements were done with different ambient and indoor air samples collected within a variety of projects or within the ambient air sampling networks of provincial governments, originating from Vienna, Styria, Carinthia, Upper Austria, and Slovenia. The sampling stations of urban air samples can be separated in urban, urban-background, and background stations. Furthermore emission samples containing particulate matter that was formed during combustion processes was analyzed. Those oxidative properties were compared with the chemical composition of the particulate matter samples (with a main focus on ions, and metals typically originating from mineral dust) as well as carbon parameters and source distributions. Clearest trends were seen for carbon parameters, with higher concentrations leading to increased depletion of ascorbate.9

Freezing on a Chip—A New Approach to Determine Heterogeneous Ice Nucleation of Micrometer-Sized Water Droplets

We are presenting a new approach to analyze the freezing behavior of aqueous droplets containing ice nucleating particles. The freezing chip consists of an etched and sputtered (15 × 15 × 1) mm gold-plated silicon or pure gold chip, enabling the formation of droplets with defined diameters between 20 and 80 µm. Several applications like an automated process control and an automated image evaluation were implemented to improve the quality of heterogeneous freezing experiments. To show the functionality of the setup, we compared freezing temperatures of aqueous droplets containing ice nucleating particles (i.e., microcline, birch pollen washing water, juniper pollen, and Snomax® solution) measured with our setup, with literature data. The ice nucleation active surface/mass site density (ns/m) of microcline, juniper pollen, and birch pollen washing water are shown to be in good agreement with literature data. Minor variations can be explained by slight differences in composition and droplet generation technique. The nm values of Snomax® differ by up to one order of magnitude at higher subzero temperatures when compared with fresh samples but are in agreement when compared with reported data of aged Snomax® samples.Fonds zur Förderung der Wissenschaftlichen Forschun

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

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

The Fifth International Workshop on Ice Nucleation phase 2 (FIN-02): laboratory intercomparison of ice nucleation measurements

© Author(s) 2018. The second phase of the Fifth International Ice Nucleation Workshop (FIN-02) involved the gathering of a large number of researchers at the Karlsruhe Institute of Technology's Aerosol Interactions and Dynamics of the Atmosphere (AIDA) facility to promote characterization and understanding of ice nucleation measurements made by a variety of methods used worldwide. Compared to the previous workshop in 2007, participation was doubled, reflecting a vibrant research area. Experimental methods involved sampling of aerosol particles by direct processing ice nucleation measuring systems from the same volume of air in separate experiments using different ice nucleating particle (INP) types, and collections of aerosol particle samples onto filters or into liquid for sharing amongst measurement techniques that post-process these samples. In this manner, any errors introduced by differences in generation methods when samples are shared across laboratories were mitigated. Furthermore, as much as possible, aerosol particle size distribution was controlled so that the size limitations of different methods were minimized. The results presented here use data from the workshop to assess the comparability of immersion freezing measurement methods activating INPs in bulk suspensions, methods that activate INPs in condensation and/or immersion freezing modes as single particles on a substrate, continuous flow diffusion chambers (CFDCs) directly sampling and processing particles well above water saturation to maximize immersion and subsequent freezing of aerosol particles, and expansion cloud chamber simulations in which liquid cloud droplets were first activated on aerosol particles prior to freezing. The AIDA expansion chamber measurements are expected to be the closest representation to INP activation in atmospheric cloud parcels in these comparisons, due to exposing particles freely to adiabatic cooling. The different particle types used as INPs included the minerals illite NX and potassium feldspar (K-feldspar), two natural soil dusts representative of arable sandy loam (Argentina) and highly erodible sandy dryland (Tunisia) soils, respectively, and a bacterial INP (Snomax®). Considered together, the agreement among post-processed immersion freezing measurements of the numbers and fractions of particles active at different temperatures following bulk collection of particles into liquid was excellent, with possible temperature uncertainties inferred to be a key factor in determining INP uncertainties. Collection onto filters for rinsing versus directly into liquid in impingers made little difference. For methods that activated collected single particles on a substrate at a controlled humidity at or above water saturation, agreement with immersion freezing methods was good in most cases, but was biased low in a few others for reasons that have not been resolved, but could relate to water vapor competition effects. Amongst CFDC-style instruments, various factors requiring (variable) higher supersaturations to achieve equivalent immersion freezing activation dominate the uncertainty between these measurements, and for comparison with bulk immersion freezing methods. When operated above water saturation to include assessment of immersion freezing, CFDC measurements often measured at or above the upper bound of immersion freezing device measurements, but often underestimated INP concentration in comparison to an immersion freezing method that first activates all particles into liquid droplets prior to cooling (the PIMCA-PINC device, or Portable Immersion Mode Cooling chAmber-Portable Ice Nucleation Chamber), and typically slightly underestimated INP number concentrations in comparison to cloud parcel expansions in the AIDA chamber; this can be largely mitigated when it is possible to raise the relative humidity to sufficiently high values in the CFDCs, although this is not always possible operationally. Correspondence of measurements of INPs among direct sampling and post-processing systems varied depending on the INP type. Agreement was best for Snomax® particles in the temperature regime colder than -10°C, where their ice nucleation activity is nearly maximized and changes very little with temperature. At temperatures warmer than -10°C, Snomax® INP measurements (all via freezing of suspensions) demonstrated discrepancies consistent with previous reports of the instability of its protein aggregates that appear to make it less suitable as a calibration INP at these temperatures. For Argentinian soil dust particles, there was excellent agreement across all measurement methods; measures ranged within 1 order of magnitude for INP number concentrations, active fractions and calculated active site densities over a 25 to 30°C range and 5 to 8 orders of corresponding magnitude change in number concentrations. This was also the case for all temperatures warmer than -25°C in Tunisian dust experiments. In contrast, discrepancies in measurements of INP concentrations or active site densities that exceeded 2 orders of magnitude across a broad range of temperature measurements found at temperatures warmer than -25°C in a previous study were replicated for illite NX. Discrepancies also exceeded 2 orders of magnitude at temperatures of -20 to -25°C for potassium feldspar (K-feldspar), but these coincided with the range of temperatures at which INP concentrations increase rapidly at approximately an order of magnitude per 2°C cooling for K-feldspar. These few discrepancies did not outweigh the overall positive outcomes of the workshop activity, nor the future utility of this data set or future similar efforts for resolving remaining measurement issues. Measurements of the same materials were repeatable over the time of the workshop and demonstrated strong consistency with prior studies, as reflected by agreement of data broadly with parameterizations of different specific or general (e.g., soil dust) aerosol types. The divergent measurements of the INP activity of illite NX by direct versus post-processing methods were not repeated for other particle types, and the Snomax° data demonstrated that, at least for a biological INP type, there is no expected measurement bias between bulk collection and direct immediately processed freezing methods to as warm as -10°C. Since particle size ranges were limited for this workshop, it can be expected that for atmospheric populations of INPs, measurement discrepancies will appear due to the different capabilities of methods for sampling the full aerosol size distribution, or due to limitations on achieving sufficient water supersaturations to fully capture immersion freezing in direct processing instruments. Overall, this workshop presents an improved picture of present capabilities for measuring INPs than in past workshops, and provides direction toward addressing remaining measurement issues

Perspectives on the Future of Ice Nucleation Research: Research Needs and Unanswered Questions Identified from Two International Workshops

There has been increasing interest in ice nucleation research in the last decade. To identify important gaps in our knowledge of ice nucleation processes and their impacts, two international workshops on ice nucleation were held in Vienna, Austria in 2015 and 2016. Experts from these workshops identified the following research needs: (1) uncovering the molecular identity of active sites for ice nucleation; (2) the importance of modeling for the understanding of heterogeneous ice nucleation; (3) identifying and quantifying contributions of biological ice nuclei from natural and managed environments; (4) examining the role of aging in ice nuclei; (5) conducting targeted sampling campaigns in clouds; and (6) designing lab and field experiments to increase our understanding of the role of ice-nucleating particles in the atmosphere. Interdisciplinary teams of scientists should work together to establish and maintain a common, unified language for ice nucleation research. A number of commercial applications benefit from ice nucleation research, including the production of artificial snow, the freezing and preservation of water-containing food products, and the potential modulation of weather. Additional work is needed to increase our understanding of ice nucleation processes and potential impacts on precipitation, water availability, climate change, crop health, and feedback cycles.© 2017 by the author