An instrument for quantifying heterogeneous ice nucleation in multiwell plates using infrared emissions to detect freezing
<p>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 0.01 L<sup>−1</sup>...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/11/5629/2018/amt-11-5629-2018.pdf |
| Summary: | <p>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 0.01 L<sup>−1</sup> 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 50 µL 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
∼ 100 µm chips of K-feldspar, by immersing these chips
in 1 µL droplets on an established cold stage (µL-NIPI) as well
as in 50 µL 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.</p> |
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| ISSN: | 1867-1381 1867-8548 |