scholarly journals Comparison of measured and calculated collision efficiencies at low temperatures

2015 ◽  
Vol 15 (23) ◽  
pp. 13759-13776 ◽  
Author(s):  
B. Nagare ◽  
C. Marcolli ◽  
O. Stetzer ◽  
U. Lohmann
Keyword(s):  
Silver Iodide ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Ice Nucleation ◽  
Brownian Diffusion ◽  
Water Droplets ◽  
Collision Efficiency ◽  
Contact Mode ◽  
Data Set ◽  
Temperature Range

Abstract. Interactions of atmospheric aerosols with clouds influence cloud properties and modify the aerosol life cycle. Aerosol particles act as cloud condensation nuclei and ice nucleating particles or become incorporated into cloud droplets by scavenging. For an accurate description of aerosol scavenging and ice nucleation in contact mode, collision efficiency between droplets and aerosol particles needs to be known. This study derives the collision rate from experimental contact freezing data obtained with the ETH CoLlision Ice Nucleation CHamber (CLINCH). Freely falling 80 μm diameter water droplets are exposed to an aerosol consisting of 200 and 400 nm diameter silver iodide particles of concentrations from 500 to 5000 and 500 to 2000 cm−3, respectively, which act as ice nucleating particles in contact mode. The experimental data used to derive collision efficiency are in a temperature range of 238–245 K, where each collision of silver iodide particles with droplets can be assumed to result in the freezing of the droplet. An upper and lower limit of collision efficiency is also estimated for 800 nm diameter kaolinite particles. The chamber is kept at ice saturation at a temperature range of 236 to 261 K, leading to the slow evaporation of water droplets giving rise to thermophoresis and diffusiophoresis. Droplets and particles bear charges inducing electrophoresis. The experimentally derived collision efficiency values of 0.13, 0.07 and 0.047–0.11 for 200, 400 and 800 nm particles are around 1 order of magnitude higher than theoretical formulations which include Brownian diffusion, impaction, interception, thermophoretic, diffusiophoretic and electric forces. This discrepancy is most probably due to uncertainties and inaccuracies in the description of thermophoretic and diffusiophoretic processes acting together. This is, to the authors' knowledge, the first data set of collision efficiencies acquired below 273 K. More such experiments with different droplet and particle diameters are needed to improve our understanding of collision processes acting together.

scholarly journals Estimating collision efficiencies from contact freezing experiments

2015 ◽  
Vol 15 (8) ◽  
pp. 12167-12212
Author(s):  
B. Nagare ◽  
C. Marcolli ◽  
O. Stetzer ◽  
U. Lohmann
Keyword(s):  
Atmospheric Aerosols ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Ice Nucleation ◽  
Brownian Diffusion ◽  
Water Droplets ◽  
Collision Efficiency ◽  
Contact Mode ◽  
Cloud Properties ◽  
Order Of Magnitude

Abstract. Interactions of atmospheric aerosols with clouds influence cloud properties and modify the aerosol life cycle. Aerosol particles act as cloud condensation nuclei and ice nucleating particles or become incorporated into cloud droplets by scavenging. For an accurate description of aerosol scavenging and ice nucleation in contact mode, collision efficiency between droplets and aerosol particles needs to be known. This study derives the collision rate from experimental contact freezing data obtained with the ETH Collision Ice Nucleation Chamber CLINCH. Freely falling 80 μm water droplets are exposed to an aerosol consisting of 200 nm diameter silver iodide particles of concentrations from 500–5000 cm−3, which act as ice nucleating particles in contact mode. The chamber is kept at ice saturation in the temperature range from 236–261 K leading to slow evaporation of water droplets giving rise to thermophoresis and diffusiophoresis. Droplets and particles bear charges inducing electrophoresis. The experimentally derived collision efficiency of 0.13 is around one order of magnitude higher than theoretical formulations which include Brownian diffusion, impaction, interception, thermophoretic, diffusiophoretic and electric forces. This discrepancy is most probably due to uncertainties and inaccuracies in the description of thermophoretic and diffusiophoretic processes acting together. This is to the authors knowledge the first dataset of collision efficiencies acquired below 273 K. More such experiments with different droplet and particle diameters are needed to improve our understanding of collision processes acting together.

scholarly journals A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets

2015 ◽  
Vol 8 (6) ◽  
pp. 2437-2447 ◽  
Author(s):  
T. F. Whale ◽  
B. J. Murray ◽  
D. O'Sullivan ◽  
T. W. Wilson ◽  
N. S. Umo ◽  
...  
Keyword(s):  
High Temperature ◽  
Silver Iodide ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Supercooled Water ◽  
Ice Nucleation ◽  
Large Droplet ◽  
Increasing Temperature ◽  
Detection And Quantification ◽  
Heterogeneous Ice Nucleation

Abstract. In many clouds, the formation of ice requires the presence of particles capable of nucleating ice. Ice-nucleating particles (INPs) are rare in comparison to cloud condensation nuclei. However, the fact that only a small fraction of aerosol particles can nucleate ice means that detection and quantification of INPs is challenging. This is particularly true at temperatures above about −20 °C since the population of particles capable of serving as INPs decreases dramatically with increasing temperature. In this paper, we describe an experimental technique in which droplets of microlitre volume containing ice-nucleating material are cooled down at a controlled rate and their freezing temperatures recorded. The advantage of using large droplet volumes is that the surface area per droplet is vastly larger than in experiments focused on single aerosol particles or cloud-sized droplets. This increases the probability of observing the effect of less common, but important, high-temperature INPs and therefore allows the quantification of their ice nucleation efficiency. The potential artefacts which could influence data from this experiment, and other similar experiments, are mitigated and discussed. Experimentally determined heterogeneous ice nucleation efficiencies for K-feldspar (microcline), kaolinite, chlorite, NX-illite, Snomax® and silver iodide are presented.

scholarly journals A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets

2014 ◽  
Vol 7 (9) ◽  
pp. 9509-9536 ◽  
Author(s):  
T. F. Whale ◽  
B. J. Murray ◽  
D. O'Sullivan ◽  
N. S. Umo ◽  
K. J. Baustian ◽  
...  
Keyword(s):  
Silver Iodide ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Supercooled Water ◽  
Ice Nucleation ◽  
Radiative Properties ◽  
Ice Content ◽  
Increasing Temperature ◽  
Mixed Phase Clouds ◽  
Heterogeneous Ice Nucleation

Abstract. The ice content of mixed phase clouds, which contain both supercooled water and ice, affects both their lifetime and radiative properties. In many clouds, the formation of ice requires the presence of particles capable of nucleating ice. One of the most important features of ice nucleating particles (INPs) is that they are rare in comparison to cloud condensation nuclei. However, the fact that only a small fraction of aerosol particles can nucleate ice means that detection and quantification of INPs is challenging. This is particularly true at temperatures above about −20 °C since the population of particles capable of serving as INPs decreases dramatically with increasing temperature. In this paper, we describe an experimental technique in which droplets of microlitre volume containing ice nucleating material are cooled down at a controlled rate and their freezing temperatures recorded. The advantage of using large droplet volumes is that the surface area per droplet is vastly larger than in experiments focused on single aerosol particles or cloud-sized droplets. This increases the probability of observing the effect of less common, but important, high temperature INPs and therefore allows the quantification of their ice nucleation efficiency. The potential artefacts which could influence data from this experiment, and other similar experiments, are mitigated and discussed. Experimentally determined heterogeneous ice nucleation efficiencies for K-feldspar (microcline), kaolinite, chlorite, Snomax®, and silver iodide are presented.

Photolytic Inactivation of Ice-Forming Silver Iodide Nuclei

1951 ◽  
Vol 32 (4) ◽  
pp. 132-135 ◽  
Author(s):  
Edward C. Y. Inn
Keyword(s):  
Surface Structure ◽  
Silver Iodide ◽  
Chemical Nature ◽  
Ice Nucleation ◽  
Water Droplets ◽  
Ice Particles ◽  
Physico Chemical ◽  
Structure Sensitive ◽  
Photolytic Decomposition

Photolytic decomposition of silver-iodide crystals has been observed when the crystals were exposed to light of wave lengths less than 4300Å, as indicated by darkening of the exposed crystals. Qualitative observations indicate exposed silver iodide crystals undergo reversible photolysis, although the exact conditions under which this takes place is not well understood. When silver iodide nuclei were similarly exposed to light, the ability to form ice particles, when injected into a cloud of super-cooled water droplets, was found to be essentially destroyed. It is believed that, as a result of photolysis of the exposed silver iodide nuclei, the physico-chemical nature of surface of the nuclei has been altered to minimize effectively the surface-structure sensitive process of ice nucleation.

scholarly journals Characterization of aerosol properties at Cyprus, focusing on cloud condensation nuclei and ice nucleating particles

2019 ◽  
Author(s):  
Xianda Gong ◽  
Heike Wex ◽  
Thomas Müller ◽  
Alfred Wiedensohler ◽  
Kristina Höhler ◽  
...  
Keyword(s):  
Size Range ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Particle Surface ◽  
Active Surface ◽  
Measured Temperature ◽  
Condensation Nuclei ◽  
Particle Surface Area ◽  
Temperature Range ◽  
Order Of Magnitude

Abstract. As part of the A-LIFE (Absorbing aerosol layers in a changing climate: aging, lifetime and dynamics) campaign, ground-based measurements were carried out in Paphos, Cyprus, for characterizing the abundance, properties and sources of aerosol particles in general, and cloud condensation nuclei (CCN) and ice nucleating particles (INP), in particular. New particle formation (NPF) events with subsequent growth of the particles into the CCN size range were observed. Aitken mode particles featured κ values of 0.21 to 0.29, indicating the presence of organic materials. Accumulation mode particles featured a higher hygroscopicity parameter, with a median κ value of 0.57, suggesting the presence of sulfate. A clear downward trend of κ with increasing supersaturation and decreasing dcrit was found. Super-micron particles originated mainly from sea spray aerosol (SSA) and partly from mineral dust. INP concentrations (NINP) were measured in the temperature range from −6.5 to −26.5 ℃, using two freezing array type instruments. NINP at a particular temperature span around 1 order of magnitude below −20 ℃, and about 2 orders of magnitude at warmer temperatures (T > −18 ℃). Few samples showed elevated concentrations at temperatures > −15 ℃, which suggests a significant contribution of biological particles to the INP population, which possibly could originate from Cyprus. Both measured temperature spectra and NINP probability density functions (PDFs) indicate that the observed INP (ice active in the temperature range between −15 and −20 ℃) mainly originate from long-range transport. There was no correlation between NINP and particle number concentration in the size range > 500 nm (N> 500 nm). Parameterizations based on N> 500 nm were found to overestimate NINP by about 1 to 2 orders of magnitude. There was also no correlation between NINP and particle surface area concentration. The ice active surface site density (ns) for the anthropogenically polluted aerosol encountered in this study is about 1 to 3 orders of magnitude lower than the ns found for dust aerosol particles in previous studies. This suggests that observed NINP-PDFs as those derived here could be a better choice for modelling NINP if the aerosol particle composition is unknown or uncertain.

scholarly journals Heterogeneous ice nucleation activity of bacteria: new laboratory experiments at simulated cloud conditions

2008 ◽  
Vol 5 (2) ◽  
pp. 1445-1468 ◽  
Author(s):  
O. Möhler ◽  
D. G. Georgakopoulos ◽  
C. E. Morris ◽  
S. Benz ◽  
V. Ebert ◽  
...  
Keyword(s):  
Pseudomonas Syringae ◽  
Cloud Condensation Nuclei ◽  
Bacterial Species ◽  
Ice Nucleation ◽  
Cloud Chamber ◽  
Bacterial Cells ◽  
Spray Formation ◽  
Temperature Range ◽  
Expansion Cooling ◽  
Activation Conditions

Abstract. The ice nucleation activities of five different Pseudomonas syringae, Pseudomonas viridiflava and Erwinia herbicola bacterial species and of SnomaxTM were investigated in the temperature range between −5 and −15°C. Water suspensions of these bacteria were directly spray into the cloud chamber of the AIDA facility of Forschungszentrum Karlsruhe at a temperature of −5.7°. At this temperature, about 1% of the SnomaxTM cells induced freezing of the spray droplets before they evaporated in the cloud chamber. The other suspensions of living cells didn't induce any measurable ice concentration during spray formation at −5.7°. The remaining aerosol was exposed to typical cloud activation conditions in subsequent experiments with expansion cooling to about −11°C. During these experiments, the bacterial cells first acted as cloud condensation nuclei to form cloud droplets and then eventually acted as ice nuclei to freeze the droplets. The results indicate that the bacteria investigated in the present study are mainly ice active in the temperature range between −7 and −11°C with an INA fraction of the order of 10−4. The ice nucleation efficiency of SnomaxTM cells was much larger with an INA fraction of 0.2 at temperatures around −8°C.

scholarly journals An overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) project: aerosol-cloud-radiation interactions in the Southeast Atlantic basin

2020 ◽  
Author(s):  
Jens Redemann ◽  
Robert Wood ◽  
Paquita Zuidema ◽  
Sarah J. Doherty ◽  
Bernadette Luna ◽  
...  
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Chemical Properties ◽  
Climate Impacts ◽  
Data Set ◽  
Aerosol Cloud ◽  
New Findings ◽  
Hemisphere Winter

Abstract. Southern Africa produces almost a third of the Earth’s biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a five-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three Intensive Observation Periods designed to study key atmospheric processes that determine the climate impacts of these aerosols. During the Southern Hemisphere winter and spring (June-October), aerosol particles reaching 3–5 km in altitude are transported westward over the South-East Atlantic, where they interact with one of the largest subtropical stratocumulus subtropical stratocumulus (Sc) cloud decks in the world. The representation of these interactions in climate models remains highly uncertain in part due to a scarcity of observational constraints on aerosol and cloud properties, and due to the parameterized treatment of physical processes. Three ORACLES deployments by the NASA P-3 aircraft in September 2016, August 2017 and October 2018 (totaling ~350 science flight hours), augmented by the deployment of the NASA ER-2 aircraft for remote sensing in September 2016 (totaling ~100 science flight hours), were intended to help fill this observational gap. ORACLES focuses on three fundamental science questions centered on the climate effects of African BB aerosols: (a) direct aerosol radiative effects; (b) effects of aerosol absorption on atmospheric circulation and clouds; (c) aerosol-cloud microphysical interactions. This paper summarizes the ORACLES science objectives, describes the project implementation, provides an overview of the flights and measurements in each deployment, and highlights the integrative modeling efforts from cloud to global scales to address science objectives. Significant new findings on the vertical structure of BB aerosol physical and chemical properties, chemical aging, cloud condensation nuclei, rain and precipitation statistics, and aerosol indirect effects are emphasized, but their detailed descriptions are the subject of separate publications. The main purpose of this paper is to familiarize the broader scientific community with the ORACLES project and the data set it produced.

Assessment of Seeding Effects in Snowpack Augmentation Programs: Ice Nucleation and Scavenging of Seeding Aerosols

1995 ◽  
Vol 34 (1) ◽  
pp. 121-130 ◽  
Author(s):  
J. A. Warburton ◽  
L. G. Young ◽  
R. H. Stone
Keyword(s):  
Sierra Nevada ◽  
Silver Iodide ◽  
Aerosol Particles ◽  
Ice Nucleation ◽  
Experimental Conditions ◽  
Winter Storms ◽  
Chemical Analysis Techniques ◽  
The Mean ◽  
Positive Correlations ◽  
Ultimate Purpose

Abstract Trace chemical analysis techniques have been used in a series of cloud-seeding experiments in the central Sierra Nevada with the ultimate purpose of distinguishing whether the submicron-sized aerosol particles used for seeding are removed by nucleation or by scavenging in snowfall. The research programs used submicron-sized seeding aerosols with different nucleating characteristics. When winter storms were seeded with silver iodide in the Lake Tahoe and Lake Almanor watersheds, positive correlations were observed between silver concentrations and precipitation amounts in both catchment areas.This is considered to be evidence that the AgI aerosols are not being removed in the snowfall entirely by scavenging processes. When two separate aerosols of silver iodide and indium sesquioxide were released simultaneously from the same ground locations during winter snowstorms in the Lake Almanor watershed, it was found that considerably more of the ice-nucleating aerosol particles (AgI) were removed by the snowfall than the non-ice-nucleating ones (In203). Under the experimental conditions employed, scavenging alone of the two aerosols would lead to a chemical ratio of Ag:In in the snowfall of 0.83:l. Ratios as high as 17.2:l were observed, the mean ratio being 4: I. These results are considered to be evidence of the removal of substantial numbers of the AgI aerosol particles through direct nucleation of ice crystals.

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