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| Titel |
A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques |
| VerfasserIn |
N. Hiranuma, S. Augustin-Bauditz, H. Bingemer, C. Budke, J. Curtius, A. Danielczok, K. Diehl, K. Dreischmeier, M. Ebert, F. Frank, N. Hoffmann, K. Kandler, A. Kiselev, T. Koop, T. Leisner, O. Möhler, B. Nillius, A. Peckhaus, D. Rose, S. Weinbruch, H. Wex, Y. Boose, P. J. DeMott, J. D. Hader, T. C. J. Hill, Z. A. Kanji, G. Kulkarni, E. J. T. Levin, C. S. McCluskey, M. Murakami, B. J. Murray, D. Niedermeier, M. D. Petters, D. O'Sullivan, A. Saito, G. P. Schill, T. Tajiri, M. A. Tolbert, A. Welti, T. F. Whale, T. P. Wright, K. Yamashita |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 5 ; Nr. 15, no. 5 (2015-03-06), S.2489-2518 |
| Datensatznummer |
250119496
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| Publikation (Nr.) |
 copernicus.org/acp-15-2489-2015.pdf |
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| Zusammenfassung |
Immersion freezing is the most relevant heterogeneous ice nucleation
mechanism through which ice crystals are formed in mixed-phase clouds. In
recent years, an increasing number of laboratory experiments utilizing a
variety of instruments have examined immersion freezing activity of
atmospherically relevant ice-nucleating particles. However, an
intercomparison of these laboratory results is a difficult task because
investigators have used different ice nucleation (IN) measurement methods to
produce these results. A remaining challenge is to explore the sensitivity
and accuracy of these techniques and to understand how the IN results are
potentially influenced or biased by experimental parameters associated with
these techniques.
Within the framework of INUIT (Ice Nuclei Research Unit), we distributed an
illite-rich sample (illite NX) as a representative surrogate for atmospheric
mineral dust particles to investigators to perform immersion freezing
experiments using different IN measurement methods and to obtain IN data as
a function of particle concentration, temperature (T), cooling rate and
nucleation time. A total of 17 measurement methods were involved in the data
intercomparison. Experiments with seven instruments started with the test
sample pre-suspended in water before cooling, while 10 other instruments
employed water vapor condensation onto dry-dispersed particles followed by
immersion freezing. The resulting comprehensive immersion freezing data set
was evaluated using the ice nucleation active surface-site density,
ns, to develop a representative ns(T) spectrum that spans a wide
temperature range (−37 °C < T < −11 °C)
and covers 9 orders of magnitude in ns.
In general, the 17 immersion freezing measurement techniques deviate,
within a range of about 8 °C in terms of temperature, by 3 orders of magnitude with respect to ns. In addition, we show evidence
that the immersion freezing efficiency expressed in ns of illite NX
particles is relatively independent of droplet size, particle mass in
suspension, particle size and cooling rate during freezing. A strong
temperature dependence and weak time and size dependence of the immersion
freezing efficiency of illite-rich clay mineral particles enabled the
ns parameterization solely as a function of temperature. We also
characterized the ns(T) spectra and identified a section with a steep
slope between −20 and −27 °C, where a large fraction of active
sites of our test dust may trigger immersion freezing. This slope was
followed by a region with a gentler slope at temperatures below −27 °C. While the agreement between different instruments was
reasonable below ~ −27 °C, there seemed to be a
different trend in the temperature-dependent ice nucleation activity from
the suspension and dry-dispersed particle measurements for this mineral
dust, in particular at higher temperatures. For instance, the ice nucleation
activity expressed in ns was smaller for the average of the wet
suspended samples and higher for the average of the dry-dispersed aerosol
samples between about −27 and −18 °C. Only instruments making
measurements with wet suspended samples were able to measure ice nucleation
above −18 °C. A possible explanation for the deviation between
−27 and −18 °C is discussed. Multiple exponential distribution
fits in both linear and log space for both specific surface area-based ns(T) and
geometric surface area-based ns(T) are provided. These new fits, constrained by using
identical reference samples, will help to compare IN measurement methods
that are not included in the present study and IN data from future IN
instruments. |
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