On the role of metal silicate molecules as ice nuclei

Abstract. Heterogeneous ice nucleation is a crucial process for forming ice-containing clouds and subsequent ice-induced precipitation. The importance for ice nucleation by airborne desert soil dusts composed predominantly of minerals is widely acknowledged. However, the potential influence of agricultural soil dusts on ice nucleation has been poorly recognized, despite recent estimates that they may account for up to 20–25% of the global atmospheric dust load. We have conducted freezing experiments with various dusts, including agricultural soil dusts derived from the largest dust-source region in North America. Here we show evidence for the significant role of soil organic matter (SOM) in particles acting as ice nuclei (IN) under mixed-phase cloud conditions. We find that the ice-nucleating ability of the agricultural soil dusts is similar to that of desert soil dusts, but is clearly reduced after either H2O2 digestion or dry heating to 300 °C. In addition, based on chemical composition analysis, we demonstrate that organic-rich particles are more important than mineral particles for the ice-nucleating ability of the agricultural soil dusts at temperatures warmer than about −36 °C. Finally, we suggest that such organic-rich particles of agricultural origin (namely, SOM particles) may contribute significantly to the ubiquity of organic-rich IN in the global atmosphere.

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Insights into the role of soot aerosols in cirrus cloud formation

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-4203-2007 ◽

2007 ◽

Vol 7 (16) ◽

pp. 4203-4227 ◽

Cited By ~ 119

Author(s):

B. Kärcher ◽

O. Möhler ◽

P. J. DeMott ◽

S. Pechtl ◽

F. Yu

Keyword(s):

Environmental Parameters ◽

Supercooled Liquid ◽

Critical Discussion ◽

Cloud Formation ◽

Cirrus Cloud ◽

Atmospheric Conditions ◽

Soot Particles ◽

Ice Nuclei ◽

Homogeneous Freezing

Abstract. Cirrus cloud formation is believed to be dominated by homogeneous freezing of supercooled liquid aerosols in many instances. Heterogeneous ice nuclei such as mineral dust, metallic, and soot particles, and some crystalline solids within partially soluble aerosols are suspected to modulate cirrus properties. Among those, the role of ubiquitous soot particles is perhaps the least understood. Because aviation is a major source of upper tropospheric soot particles, we put emphasis on ice formation in dispersing aircraft plumes. The effect of aircraft soot on cirrus formation in the absence of contrails is highly complex and depends on a wide array of emission and environmental parameters. We use a microphysical-chemical model predicting the formation of internally mixed, soot-containing particles up to two days after emission, and suggest two principal scenarios: high concentrations of original soot emissions could slightly increase the number of ice crystals; low concentrations of particles originating from coagulation of emitted soot with background aerosols could lead to a significant reduction in ice crystal number. Both scenarios assume soot particles to be moderate ice nuclei relative to cirrus formation by homogeneous freezing in the presence of few efficient dust ice nuclei. A critical discussion of laboratory experiments reveals that the ice nucleation efficiency of soot particles depends strongly on their source, and, by inference, on atmospheric aging processes. Mass and chemistry of soluble surface coatings appear to be crucial factors. Immersed soot particles tend to be poor ice nuclei, some bare ones nucleate ice at low supersaturations. However, a fundamental understanding of these studies is lacking, rendering extrapolations to atmospheric conditions speculative. In particular, we cannot yet decide which indirect aircraft effect scenario is more plausible, and options suggested to mitigate the problem remain uncertain.

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Cirrus cloud formation and the role of heterogeneous ice nuclei

10.1063/1.4803436 ◽

2013 ◽

Cited By ~ 2

Author(s):

Karl D. Froyd ◽

Daniel J. Cziczo ◽

Corinna Hoose ◽

Eric J. Jensen ◽

Minghui Diao ◽

...

Keyword(s):

Cloud Formation ◽

Cirrus Cloud ◽

Ice Nuclei

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Influence of the ambient humidity on the concentration of natural deposition ice nuclei

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-16697-2015 ◽

2015 ◽

Vol 15 (12) ◽

pp. 16697-16714

Author(s):

M. L. López ◽

E. E. Ávila

Keyword(s):

Relative Humidity ◽

Linear Trend ◽

Ground Level ◽

Air Masses ◽

Ambient Humidity ◽

Ambient Relative Humidity ◽

Ice Nuclei ◽

Thermodynamic Conditions ◽

Rainy Days

Abstract. This study reports measurements of deposition ice nuclei (IN) concentration at ground level during the period July–December 2014 in Córdoba, Argentina. The measurements were carried out at temperature of −25 °C and at 15 % supersaturation over ice. They were performed on days with different thermodynamic conditions, including rainy days. The effect of the relative humidity at ground level (RHamb) on the IN concentration was analyzed. The number of IN activated varied from 1 −1 at RHamb of 25 % to 30 L−1 at RHamb of 90 %. In general, a linear trend between the IN concentration and the RHamb was found, suggesting that this variable must be related to the ability of the aerosols acting as IN. These results are consistent with previous results. From the backward trajectories analysis, it was found that the link between IN concentration and RHamb is independent of the origin of the air masses. The role of nucleation occurring in pores and cavities was discussed as possible mechanism to explain the increase on the IN concentration during high ambient relative humidity events.

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Insights into the role of soot aerosols in cirrus cloud formation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-7843-2007 ◽

2007 ◽

Vol 7 (3) ◽

pp. 7843-7905 ◽

Cited By ~ 5

Author(s):

B. Kärcher ◽

O. Möhler ◽

P. J. DeMott ◽

S. Pechtl ◽

F. Yu

Keyword(s):

Environmental Parameters ◽

Supercooled Liquid ◽

Critical Discussion ◽

Cloud Formation ◽

Cirrus Cloud ◽

Atmospheric Conditions ◽

Soot Particles ◽

Ice Nuclei ◽

Homogeneous Freezing

Abstract. Cirrus cloud formation is believed to be domi\\-nated by homogeneous freezing of supercooled liquid aerosols in many instances. Heterogeneous ice nuclei such as mineral dust, metallic, and soot particles, and some crystalline solids within partially soluble aerosols are suspected to modulate cirrus properties. Among those, the role of ubiqui\\-tous soot particles is perhaps the least understood. Because aviation is a major source of upper tropospheric soot particles, we put emphasis on ice formation in dispersing aircraft plumes. The effect of aircraft soot on cirrus formation in the absence of contrails is highly complex and depends on a wide array of emission and environmental parameters. We use a microphysical-chemical model predicting the formation of internally mixed, soot-containing particles up to two days after emission, and suggest two principal scenarios, both assuming soot particles to be moderate ice nuclei relative to cirrus formation by homogeneous freezing in the presence of few efficient dust ice nuclei: high concentrations of original soot emissions could slightly increase the number of ice crystals; low concentrations of particles originating from coagulation of emitted soot with background aerosols could lead to a significant reduction in ice crystal number. A critical discussion of laboratory experiments reveals that the ice nucleation efficiency of soot particles depends strongly on their source, and, by inference, on atmospheric aging processes. Mass and chemistry of soluble surface coatings appear to be crucial factors. Immersed soot particles tend to be poor ice nuclei, some bare ones nucleate ice at low supersaturations. However, a fundamental understanding of these studies is lacking, rendering extrapolations to atmospheric conditions speculative. In particular, we cannot yet decide which indirect aircraft effect scenario is more plausible, and options suggested to mitigate the problem remain uncertain.

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Assessment of a Microphysical Ensemble Used to Investigate the OWLeS IOP4 Lake-Effect Storm

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0045.1 ◽

2021 ◽

Author(s):

Lauriana C. Gaudet ◽

Kara J. Sulia ◽

Tzu-Chin Tsai ◽

Jen-Ping Chen ◽

Jessica P. Blair

Keyword(s):

Liquid Water Content ◽

Weather Research And Forecasting ◽

Microphysics Scheme ◽

Convective Clouds ◽

Cloud Properties ◽

Ice Nuclei ◽

Lake Effect ◽

Microphysical Processes ◽

Snow And Ice

AbstractMicrophysical processes within mixed-phase convective clouds can have cascading impacts on cloud properties and resultant precipitation. This paper investigates the role of microphysics in the lake-effect storm (LES) observed during intensive observing period 4 of the Ontario Winter Lake-effect Systems field campaign. A microphysical ensemble is composed of 24 simulations that differ in the microphysics scheme used (e.g., Weather Research and Forecasting Model microphysics options or a choice of two bulk adaptive habit models) along with changes in the representation of aerosol and potential ice nuclei concentrations, ice nucleation parameterizations, rain and ice fall speeds, spectral indices, ice habit assumptions, and the number of moments used for modeling ice-phase hydrometeors in each adaptive habit model. Each of these changes to microphysics resulted in varied precipitation types at the surface; 15 members forecast a mixture of snow, ice, and graupel, seven members forecast only snow and ice, and the remaining two members forecast a combination of snow, ice, graupel, and rain. Observations from an optical disdrometer positioned to the south of the LES core indicate that 92% of the observed particles were snow and ice, 5% were graupel, and 3% were rain and drizzle. Analysis of observations spanning more than a point location, such as polarimetric radar observations and aircraft measurements of liquid water content, provides insight into cloud composition and processes leading to the differences at the surface. Ensemble spread is controlled by hydrometeor type differences spurred by processes or parameters (e.g., ice fall speed) that affect graupel mass.

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