Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory
Homogeneous nucleation of ice in supercooled water droplets is a stochastic process. In its classical description, the growth of the ice phase requires the emergence of a critical embryo from random fluctuations of water molecules between the water bulk and ice-like clusters, which is associated wit...
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Copernicus Publications
2017-03-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | http://www.atmos-chem-phys.net/17/3525/2017/acp-17-3525-2017.pdf |
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Article |
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DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
L. Kaufmann C. Marcolli B. Luo T. Peter |
spellingShingle |
L. Kaufmann C. Marcolli B. Luo T. Peter Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory Atmospheric Chemistry and Physics |
author_facet |
L. Kaufmann C. Marcolli B. Luo T. Peter |
author_sort |
L. Kaufmann |
title |
Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory |
title_short |
Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory |
title_full |
Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory |
title_fullStr |
Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory |
title_full_unstemmed |
Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory |
title_sort |
refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2017-03-01 |
description |
Homogeneous nucleation of ice in supercooled water
droplets is a stochastic process. In its classical description, the growth
of the ice phase requires the emergence of a critical embryo from random
fluctuations of water molecules between the water bulk and ice-like
clusters, which is associated with overcoming an energy barrier. For
heterogeneous ice nucleation on ice-nucleating surfaces both stochastic and
deterministic descriptions are in use. Deterministic (singular) descriptions
are often favored because the temperature dependence of ice nucleation on a
substrate usually dominates the stochastic time dependence, and the ease of
representation facilitates the incorporation in climate models. Conversely,
classical nucleation theory (CNT) describes heterogeneous ice nucleation as
a stochastic process with a reduced energy barrier for the formation of a
critical embryo in the presence of an ice-nucleating surface. The energy
reduction is conveniently parameterized in terms of a contact angle
<i>α</i> between the ice phase immersed in liquid water and the
heterogeneous surface. This study investigates various ice-nucleating agents
in immersion mode by subjecting them to repeated freezing cycles to
elucidate and discriminate the time and temperature dependences of
heterogeneous ice nucleation. Freezing rates determined from such refreeze
experiments are presented for Hoggar Mountain dust, birch pollen washing
water, Arizona test dust (ATD), and also nonadecanol coatings. For
the analysis of the experimental data with CNT, we assumed the same active
site to be always responsible for freezing. Three different CNT-based
parameterizations were used to describe rate coefficients for heterogeneous
ice nucleation as a function of temperature, all leading to very similar
results: for Hoggar Mountain dust, ATD, and larger nonadecanol-coated water
droplets, the experimentally determined increase in freezing rate with
decreasing temperature is too shallow to be described properly by CNT using
the contact angle <i>α</i> as the only fit parameter. Conversely,
birch pollen washing water and small nonadecanol-coated water droplets show
temperature dependencies of freezing rates steeper than predicted by all
three CNT parameterizations. Good agreement of observations and calculations
can be obtained when a pre-factor <i>β</i> is introduced to the rate
coefficient as a second fit parameter. Thus, the following microphysical
picture emerges: heterogeneous freezing occurs at ice-nucleating sites that
need a minimum (critical) surface area to host embryos of critical size to
grow into a crystal. Fits based on CNT suggest that the critical active site
area is in the range of 10–50 nm<sup>2</sup>, with the exact value depending on
sample, temperature, and CNT-based parameterization. Two fitting parameters
are needed to characterize individual active sites. The contact angle
<i>α</i> lowers the energy barrier that has to be
overcome to form the critical embryo at the site compared to the homogeneous
case where the critical embryo develops in the volume of water. The
pre-factor <i>β</i> is needed to adjust the calculated slope of
freezing rate increase with temperature decrease. When this slope is steep,
this can be interpreted as a high frequency of nucleation attempts, so that
nucleation occurs immediately when the temperature is low enough for the
active site to accommodate a critical embryo. This is the case for active
sites of birch pollen washing water and for small droplets coated with
nonadecanol. If the pre-factor is low, the frequency of nucleation attempts
is low and the increase in freezing rate with decreasing temperature is
shallow. This is the case for Hoggar Mountain dust, the large droplets
coated with nonadecanol, and ATD. Various hypotheses why the value of the
pre-factor depends on the nature of the active sites are discussed. |
url |
http://www.atmos-chem-phys.net/17/3525/2017/acp-17-3525-2017.pdf |
work_keys_str_mv |
AT lkaufmann refreezeexperimentswithwaterdropletscontainingdifferenttypesoficenucleiinterpretedbyclassicalnucleationtheory AT cmarcolli refreezeexperimentswithwaterdropletscontainingdifferenttypesoficenucleiinterpretedbyclassicalnucleationtheory AT bluo refreezeexperimentswithwaterdropletscontainingdifferenttypesoficenucleiinterpretedbyclassicalnucleationtheory AT tpeter refreezeexperimentswithwaterdropletscontainingdifferenttypesoficenucleiinterpretedbyclassicalnucleationtheory |
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1725949547547459584 |
spelling |
doaj-135b46f5748a4ce0bbcabcc9e68d25442020-11-24T21:34:25ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242017-03-011753525355210.5194/acp-17-3525-2017Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theoryL. Kaufmann0C. Marcolli1B. Luo2T. Peter3Institute for Atmospheric and Climate Science, ETH, Zurich, SwitzerlandInstitute for Atmospheric and Climate Science, ETH, Zurich, SwitzerlandInstitute for Atmospheric and Climate Science, ETH, Zurich, SwitzerlandInstitute for Atmospheric and Climate Science, ETH, Zurich, SwitzerlandHomogeneous nucleation of ice in supercooled water droplets is a stochastic process. In its classical description, the growth of the ice phase requires the emergence of a critical embryo from random fluctuations of water molecules between the water bulk and ice-like clusters, which is associated with overcoming an energy barrier. For heterogeneous ice nucleation on ice-nucleating surfaces both stochastic and deterministic descriptions are in use. Deterministic (singular) descriptions are often favored because the temperature dependence of ice nucleation on a substrate usually dominates the stochastic time dependence, and the ease of representation facilitates the incorporation in climate models. Conversely, classical nucleation theory (CNT) describes heterogeneous ice nucleation as a stochastic process with a reduced energy barrier for the formation of a critical embryo in the presence of an ice-nucleating surface. The energy reduction is conveniently parameterized in terms of a contact angle <i>α</i> between the ice phase immersed in liquid water and the heterogeneous surface. This study investigates various ice-nucleating agents in immersion mode by subjecting them to repeated freezing cycles to elucidate and discriminate the time and temperature dependences of heterogeneous ice nucleation. Freezing rates determined from such refreeze experiments are presented for Hoggar Mountain dust, birch pollen washing water, Arizona test dust (ATD), and also nonadecanol coatings. For the analysis of the experimental data with CNT, we assumed the same active site to be always responsible for freezing. Three different CNT-based parameterizations were used to describe rate coefficients for heterogeneous ice nucleation as a function of temperature, all leading to very similar results: for Hoggar Mountain dust, ATD, and larger nonadecanol-coated water droplets, the experimentally determined increase in freezing rate with decreasing temperature is too shallow to be described properly by CNT using the contact angle <i>α</i> as the only fit parameter. Conversely, birch pollen washing water and small nonadecanol-coated water droplets show temperature dependencies of freezing rates steeper than predicted by all three CNT parameterizations. Good agreement of observations and calculations can be obtained when a pre-factor <i>β</i> is introduced to the rate coefficient as a second fit parameter. Thus, the following microphysical picture emerges: heterogeneous freezing occurs at ice-nucleating sites that need a minimum (critical) surface area to host embryos of critical size to grow into a crystal. Fits based on CNT suggest that the critical active site area is in the range of 10–50 nm<sup>2</sup>, with the exact value depending on sample, temperature, and CNT-based parameterization. Two fitting parameters are needed to characterize individual active sites. The contact angle <i>α</i> lowers the energy barrier that has to be overcome to form the critical embryo at the site compared to the homogeneous case where the critical embryo develops in the volume of water. The pre-factor <i>β</i> is needed to adjust the calculated slope of freezing rate increase with temperature decrease. When this slope is steep, this can be interpreted as a high frequency of nucleation attempts, so that nucleation occurs immediately when the temperature is low enough for the active site to accommodate a critical embryo. This is the case for active sites of birch pollen washing water and for small droplets coated with nonadecanol. If the pre-factor is low, the frequency of nucleation attempts is low and the increase in freezing rate with decreasing temperature is shallow. This is the case for Hoggar Mountain dust, the large droplets coated with nonadecanol, and ATD. Various hypotheses why the value of the pre-factor depends on the nature of the active sites are discussed.http://www.atmos-chem-phys.net/17/3525/2017/acp-17-3525-2017.pdf |