Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline
Potassium-containing feldspars (K-feldspars) have been considered as key mineral dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the effect of solutes on their IN efficiency, we performed immersion freezing experiments with the K-feldspar microcline, which is highly IN active....
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Copernicus Publications
2018-05-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/7057/2018/acp-18-7057-2018.pdf |
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DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
A. Kumar C. Marcolli B. Luo T. Peter |
spellingShingle |
A. Kumar C. Marcolli B. Luo T. Peter Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline Atmospheric Chemistry and Physics |
author_facet |
A. Kumar C. Marcolli B. Luo T. Peter |
author_sort |
A. Kumar |
title |
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline |
title_short |
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline |
title_full |
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline |
title_fullStr |
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline |
title_full_unstemmed |
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline |
title_sort |
ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – part 1: the k-feldspar microcline |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2018-05-01 |
description |
Potassium-containing feldspars (K-feldspars) have been considered as key mineral
dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the
effect of solutes on their IN efficiency, we performed immersion freezing
experiments with the K-feldspar microcline, which is highly IN active.
Freezing of emulsified droplets with microcline suspended in aqueous
solutions of NH<sub>3</sub>, (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>, NH<sub>4</sub>HSO<sub>4</sub>,
NH<sub>4</sub>NO<sub>3</sub>, NH<sub>4</sub>Cl, Na<sub>2</sub>SO<sub>4</sub>,
H<sub>2</sub>SO<sub>4</sub>, K<sub>2</sub>SO<sub>4</sub> and KCl, with solute concentrations
corresponding to water activities <i>a</i><sub>w</sub> = 0.9–1.0, were
investigated by means of a differential scanning calorimeter (DSC). The
measured heterogeneous IN onset temperatures,
<i>T</i><sub>het</sub>(<i>a</i><sub>w</sub>), deviate strongly from
<i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>), the
values calculated from the water-activity-based approach (where
<i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>) = <i>T</i><sub>melt</sub>(<i>a</i><sub>w</sub> + Δ<i>a</i><sub>w</sub><sup>het</sup>) with a constant offset Δ<i>a</i><sub>w</sub><sup>het</sup> with respect to the ice melting point curve).
Surprisingly, for very dilute solutions of NH<sub>3</sub> and
NH<sub>4</sub><sup>+</sup> salts (molalities <i>≲</i>1 mol kg<sup>−1</sup>
corresponding to <i>a</i><sub>w</sub> <i>≳</i> 0.96), we find IN
temperatures raised by up to 4.5 K above the onset freezing temperature of
microcline in pure water (<i>T</i><sub>het</sub>(<i>a</i><sub>w</sub> = 1)) and 5.5 K
above <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>),
revealing NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> to significantly enhance the IN
of the microcline surface. Conversely, more concentrated NH<sub>3</sub> and
NH<sub>4</sub><sup>+</sup> solutions show a depression of the onset temperature below
<i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>) by as
much as 13.5 K caused by a decline in IN ability accompanied with a
reduction in the volume fraction of water frozen heterogeneously. All salt
solutions not containing NH<sub>4</sub><sup>+</sup> as cation exhibit nucleation
temperatures <i>T</i><sub>het</sub>(<i>a</i><sub>w</sub>) < <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>) even at very small solute
concentrations. In all these cases, the heterogeneous freezing peak displays
a decrease as solute concentration increases. This deviation from Δ<i>a</i><sub>w</sub><sup>het</sup> = const. indicates specific chemical
interactions between particular solutes and the microcline surface not
captured by the water-activity-based approach. One such interaction is the
exchange of K<sup>+</sup> available on the microcline surface with externally
added cations (e.g., NH<sub>4</sub><sup>+</sup>). However, the presence of a similar
increase in IN efficiency in dilute ammonia solutions indicates that the
cation exchange cannot explain the increase in IN temperatures. Instead, we
hypothesize that NH<sub>3</sub> molecules hydrogen bonded on the microcline
surface form an ice-like overlayer, which provides hydrogen bonding favorable
for ice to nucleate on, thus enhancing both the freezing temperatures and the
heterogeneously frozen fraction in dilute NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup>
solutions. Moreover, we show that aging of microcline in concentrated
solutions over several days does not impair IN efficiency permanently in case
of near-neutral solutions since most of it recovers when aged particles are
resuspended in pure water. In contrast, exposure to severe acidity
(pH <i>≲</i>1.2) or alkalinity (pH <i>≳</i>11.7) damages
the microcline surface, hampering or even destroying the IN efficiency
irreversibly. Implications for IN in airborne dust containing microcline
might be multifold, ranging from a reduction of immersion freezing when
exposed to dry, cold and acidic conditions to a 5 K enhancement during
condensation freezing when microcline particles experience high humidity
(<i>a</i><sub>w</sub><i>≳</i>0.96) at warm (252–257 K) and
NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup>-rich conditions. |
url |
https://www.atmos-chem-phys.net/18/7057/2018/acp-18-7057-2018.pdf |
work_keys_str_mv |
AT akumar icenucleationactivityofsilicatesandaluminosilicatesinpurewaterandaqueoussolutionspart1thekfeldsparmicrocline AT cmarcolli icenucleationactivityofsilicatesandaluminosilicatesinpurewaterandaqueoussolutionspart1thekfeldsparmicrocline AT bluo icenucleationactivityofsilicatesandaluminosilicatesinpurewaterandaqueoussolutionspart1thekfeldsparmicrocline AT tpeter icenucleationactivityofsilicatesandaluminosilicatesinpurewaterandaqueoussolutionspart1thekfeldsparmicrocline |
_version_ |
1725482551022190592 |
spelling |
doaj-3dbdda4095084a39a83f8fce90dd3bc72020-11-24T23:49:23ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242018-05-01187057707910.5194/acp-18-7057-2018Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microclineA. Kumar0C. Marcolli1B. Luo2T. Peter3Institute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandInstitute for Atmospheric and Climate Sciences, ETH Zurich, Zurich, 8092, SwitzerlandPotassium-containing feldspars (K-feldspars) have been considered as key mineral dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the effect of solutes on their IN efficiency, we performed immersion freezing experiments with the K-feldspar microcline, which is highly IN active. Freezing of emulsified droplets with microcline suspended in aqueous solutions of NH<sub>3</sub>, (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>, NH<sub>4</sub>HSO<sub>4</sub>, NH<sub>4</sub>NO<sub>3</sub>, NH<sub>4</sub>Cl, Na<sub>2</sub>SO<sub>4</sub>, H<sub>2</sub>SO<sub>4</sub>, K<sub>2</sub>SO<sub>4</sub> and KCl, with solute concentrations corresponding to water activities <i>a</i><sub>w</sub> = 0.9–1.0, were investigated by means of a differential scanning calorimeter (DSC). The measured heterogeneous IN onset temperatures, <i>T</i><sub>het</sub>(<i>a</i><sub>w</sub>), deviate strongly from <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>), the values calculated from the water-activity-based approach (where <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>) = <i>T</i><sub>melt</sub>(<i>a</i><sub>w</sub> + Δ<i>a</i><sub>w</sub><sup>het</sup>) with a constant offset Δ<i>a</i><sub>w</sub><sup>het</sup> with respect to the ice melting point curve). Surprisingly, for very dilute solutions of NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> salts (molalities <i>≲</i>1 mol kg<sup>−1</sup> corresponding to <i>a</i><sub>w</sub> <i>≳</i> 0.96), we find IN temperatures raised by up to 4.5 K above the onset freezing temperature of microcline in pure water (<i>T</i><sub>het</sub>(<i>a</i><sub>w</sub> = 1)) and 5.5 K above <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>), revealing NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> to significantly enhance the IN of the microcline surface. Conversely, more concentrated NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> solutions show a depression of the onset temperature below <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>) by as much as 13.5 K caused by a decline in IN ability accompanied with a reduction in the volume fraction of water frozen heterogeneously. All salt solutions not containing NH<sub>4</sub><sup>+</sup> as cation exhibit nucleation temperatures <i>T</i><sub>het</sub>(<i>a</i><sub>w</sub>) < <i>T</i><sub>het</sub><sup>Δ<i>a</i><sub>w</sub><sup>het</sup></sup>(<i>a</i><sub>w</sub>) even at very small solute concentrations. In all these cases, the heterogeneous freezing peak displays a decrease as solute concentration increases. This deviation from Δ<i>a</i><sub>w</sub><sup>het</sup> = const. indicates specific chemical interactions between particular solutes and the microcline surface not captured by the water-activity-based approach. One such interaction is the exchange of K<sup>+</sup> available on the microcline surface with externally added cations (e.g., NH<sub>4</sub><sup>+</sup>). However, the presence of a similar increase in IN efficiency in dilute ammonia solutions indicates that the cation exchange cannot explain the increase in IN temperatures. Instead, we hypothesize that NH<sub>3</sub> molecules hydrogen bonded on the microcline surface form an ice-like overlayer, which provides hydrogen bonding favorable for ice to nucleate on, thus enhancing both the freezing temperatures and the heterogeneously frozen fraction in dilute NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup> solutions. Moreover, we show that aging of microcline in concentrated solutions over several days does not impair IN efficiency permanently in case of near-neutral solutions since most of it recovers when aged particles are resuspended in pure water. In contrast, exposure to severe acidity (pH <i>≲</i>1.2) or alkalinity (pH <i>≳</i>11.7) damages the microcline surface, hampering or even destroying the IN efficiency irreversibly. Implications for IN in airborne dust containing microcline might be multifold, ranging from a reduction of immersion freezing when exposed to dry, cold and acidic conditions to a 5 K enhancement during condensation freezing when microcline particles experience high humidity (<i>a</i><sub>w</sub><i>≳</i>0.96) at warm (252–257 K) and NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup>-rich conditions.https://www.atmos-chem-phys.net/18/7057/2018/acp-18-7057-2018.pdf |