11 Nov 2020

11 Nov 2020

Review status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Development of the drop Freezing Ice Nuclei Counter (FINC), intercomparison of droplet freezing techniques, and use of soluble lignin as an atmospheric ice nucleation standard

Anna J. Miller1,, Killian P. Brennan2,, Claudia Mignani3, Jörg Wieder2, Robert O. David4, and Nadine Borduas-Dedekind1,2 Anna J. Miller et al.
  • 1Institute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, 8092 Switzerland
  • 2Institute for Atmosphere and Climate Science, ETH Zurich, Zurich, 8092 Switzerland
  • 3Department of Environmental Sciences, University of Basel, Basel, 4056 Switzerland
  • 4Department of Geosciences, University of Oslo, Oslo, 0315 Norway
  • These authors contributed equally to this work.

Abstract. Aerosol-cloud interactions, including the ice nucleation of supercooled liquid water droplets caused by ice nucleating particles (INPs) and macromolecules (INMs), are a source of uncertainty in predicting future climate. Because of INPs' and INMs' spatial and temporal heterogeneity in source, number, and composition, predicting their concentration and distribution is a challenge, requiring apt analytical instrumentation. Here, we present the development of our drop Freezing Ice Nucleation Counter (FINC), a droplet freezing technique (DFT), for the quantification of INP and INM concentrations in the immersion freezing mode. FINC's design builds upon previous DFTs and uses an ethanol bath to cool sample aliquots while detecting freezing using a camera. Specifically, FINC uses 288 sample wells of 5–60 μL volume, has a limit of detection of −25.37 ± 0.15 °C with 5 μL, and has an instrument temperature uncertainty of ±0.5 °C. We further conducted freezing control experiments to quantify the non-homogeneous behavior of our developed DFT, including the consideration of eight different sources of contamination.

As part of the validation of FINC, an intercomparison campaign was conducted using an NX-illite suspension and an ambient aerosol sample with two other drop-freezing instruments: ETH's DRoplet Ice Nuclei Counter Zurich (DRINCZ) and University of Basel's LED-based ice nucleation detection apparatus (LINDA). We also tabulated an exhaustive list of peer-reviewed DFTs, to which we added our characterized and validated FINC.

In addition, we propose herein the use of a water-soluble biopolymer, lignin, as a suitable ice nucleating standard. An ideal INM standard should be inexpensive, accessible, reproducible, unaffected by sample preparation, and consistent across techniques. First, we compare its freezing temperature across different drop-freezing instruments, including on DRINCZ and LINDA, and determine an empirical fit parameter for future drop freezing validations. Second, we show that commercial lignin has a consistent ice nucleating activity across product batches. Third, we demonstrate that the ice nucleating ability of aqueous lignin solutions are stable over time. With these findings, we aim to show that lignin can be used as a good immersion freezing standard in future technique intercomparisons in the field of atmospheric ice nucleation.

Anna J. Miller et al.

Anna J. Miller et al.

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Development of the drop Freezing Ice Nuclei Counter (FINC), intercomparison of drop freezing instruments, and use of soluble lignin as an atmospheric ice nucleation standard Miller, Anna J., Brennan, Killian P., Mignani, Claudia, Wieder, Jörg, David, Robert O., and Borduas-Dedekind, Nadine

Anna J. Miller et al.


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Short summary
For characterizing atmospheric ice nuclei, we present (1) the development of our home-built droplet freezing technique (DFT), the Freezing Ice Nuclei Counter (FINC), (2) an intercomparison campaign using NX-illite and an ambient sample with two other DFTs, and (3) the application of lignin as a soluble and commercial ice nuclei standard with three DFTs. We further compiled the growing number of DFTs in use for atmospheric ice nucleation since 2000, to which we add FINC.