Cleaning up our water: reducing interferences from nonhomogeneous freezing of “pure” water in droplet freezing assays of ice-nucleating particles
<p>Droplet freezing techniques (DFTs) have been used for half a century to measure the concentration of ice-nucleating particles (INPs) in the atmosphere and determine their freezing properties to understand the effects of INPs on mixed-phase clouds. The ice nucleation community has recentl...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/11/5315/2018/amt-11-5315-2018.pdf |
| Summary: | <p>Droplet freezing techniques (DFTs) have been used for half a century to
measure the concentration of ice-nucleating particles (INPs) in the atmosphere
and determine their freezing properties to understand the effects of INPs on
mixed-phase clouds. The ice nucleation community has recently adopted droplet
freezing assays as a commonplace experimental approach. These droplet
freezing experiments are often limited by contamination that causes
nonhomogeneous freezing of the <q>pure</q> water used to generate the droplets
in the heterogeneous freezing temperature regime that is being measured.
Interference from the early freezing of water is often overlooked and not
fully reported, or measurements are restricted to analyzing the more
ice-active INPs that freeze well above the temperature of the background
water. However, this avoidance is not viable for analyzing the freezing
behavior of less active INPs in the atmosphere that still have potentially
important effects on cold-cloud microphysics. In this work we review a number
of recent droplet freezing techniques that show great promise in reducing these
interferences, and we report our own extensive series of measurements using
similar methodologies. By characterizing the performance of different
substrates on which the droplets are placed and of different pure water
generation techniques, we recommend best practices to reduce these
interferences. We tested different substrates, water sources, droplet
matrixes, and droplet sizes to provide deeper insight into what methodologies
are best suited for DFTs. Approaches for analyzing droplet freezing
temperature spectra and accounting and correcting for the background <q>pure</q>
water control spectrum are also presented. Finally, we propose experimental
and data analysis procedures for future homogeneous and heterogeneous ice
nucleation studies to promote a more uniform and reliable methodology that
facilitates the ready intercomparison of ice-nucleating particles measured by
DFTs.</p> |
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| ISSN: | 1867-1381 1867-8548 |