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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 10 | Copyright

Special issue: Fifth International Workshop on Ice Nucleation (FIN) (ACP/AMT...

Atmos. Meas. Tech., 11, 5629-5641, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Oct 2018

Research article | 15 Oct 2018

An instrument for quantifying heterogeneous ice nucleation in multiwell plates using infrared emissions to detect freezing

Alexander D. Harrison1, Thomas F. Whale1,a, Rupert Rutledge2, Stephen Lamb2, Mark D. Tarn1, Grace C. E. Porter1, Michael P. Adams1, James B. McQuaid1, George J. Morris2, and Benjamin J. Murray1 Alexander D. Harrison et al.
  • 1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
  • 2Asymptote Ltd., GE Healthcare, Sovereign House, Cambridge, CB24 9BZ, UK
  • anow at: School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK

Abstract. Low concentrations of ice-nucleating particles (INPs) are thought to be important for the properties of mixed-phase clouds, but their detection is challenging. Hence, there is a need for instruments where INP concentrations of less than 0.01L−1 can be routinely and efficiently determined. The use of larger volumes of suspension in drop assays increases the sensitivity of an experiment to rarer INPs or rarer active sites due to the increase in aerosol or surface area of particulates per droplet. Here we describe and characterise the InfraRed-Nucleation by Immersed Particles Instrument (IR-NIPI), a new immersion freezing assay that makes use of IR emissions to determine the freezing temperature of individual 50µL droplets each contained in a well of a 96-well plate. Using an IR camera allows the temperature of individual aliquots to be monitored. Freezing temperatures are determined by detecting the sharp rise in well temperature associated with the release of heat caused by freezing. In this paper we first present the calibration of the IR temperature measurement, which makes use of the fact that following ice nucleation aliquots of water warm to the ice–liquid equilibrium temperature (i.e. 0°C when water activity is ∼1), which provides a point of calibration for each individual well in each experiment. We then tested the temperature calibration using ∼100µm chips of K-feldspar, by immersing these chips in 1µL droplets on an established cold stage (µL-NIPI) as well as in 50µL droplets on IR-NIPI; the results were consistent with one another, indicating no bias in the reported freezing temperature. In addition we present measurements of the efficiency of the mineral dust NX-illite and a sample of atmospheric aerosol collected on a filter in the city of Leeds. NX-illite results are consistent with literature data, and the atmospheric INP concentrations were in good agreement with the results from the µL-NIPI instrument. This demonstrates the utility of this approach, which offers a relatively high throughput of sample analysis and access to low INP concentrations.

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The detection of low concentrations of ice-nucleating particles (INPs) is challenging. Here we present a new technique (IR-NIPI) that is sensitive to low concentrations of INPs (> 0.01 L−1) and uses an infrared camera with a novel calibration to detect the freezing of experimental suspensions. IR-NIPI temperature measurements prove to be robust with a series of comparisons to thermocouple measurements. Experimental comparisons to other freezing assay instruments are also in agreement.
The detection of low concentrations of ice-nucleating particles (INPs) is challenging. Here we...