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 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 Review and uncertainty assessment of size-resolved scavenging coefficient formulations for snow scavenging of atmospheric aerosols

2013 ◽  
Vol 13 (6) ◽  
pp. 14823-14869 ◽  
Author(s):  
L. Zhang ◽  
X. Wang ◽  
M. D. Moran ◽  
J. Feng
Keyword(s):  
Atmospheric Aerosols ◽  
Atmospheric Aerosol ◽  
Collection Efficiency ◽  
Aerosol Particles ◽  
Field Measurements ◽  
Cross Sectional ◽  
Atmospheric Aerosol Particles ◽  
Order Of Magnitude ◽  
Snow Particle ◽  
Scavenging Coefficient

Abstract. Theoretical parameterizations for the size-resolved scavenging coefficient for atmospheric aerosol particles scavenged by snow (Λsnow) need assumptions regarding (i) snow particle–aerosol particle collection efficiency E, (ii) snow particle size distribution N(Dp), (iii) snow particle terminal velocity VD, and (iv) snow particle cross-sectional area A. Existing formulas for these parameters are reviewed in the present study and uncertainties in Λsnow caused by various combinations of these parameters are assessed. Different formulations of E can cause uncertainties in Λsnow of more than one order of magnitude for all aerosol sizes for typical snowfall intensities. E is the largest source of uncertainty among all the input parameters, similar to rain scavenging of atmospheric aerosols (Λrain) as was found in a previous study by Wang et al. (2010). However, other parameters can also cause significant uncertainties in Λsnow, and the uncertainties from these parameters are much larger than for Λrain. Specifically, different N(Dp) formulations can cause one-order-of-magnitude uncertainties in Λsnow for all aerosol sizes, as is also the case for a combination of uncertainties from both VD and A. In comparison, uncertainties in Λrain from N(Dp) are smaller than a factor of 5 and those from VD are smaller than a factor of 2. Λsnow estimated from one empirical formula generated from field measurements falls in the upper range of, or is slightly higher than, theoretically estimated values. The predicted aerosol concentrations obtained using different Λsnow formulas can differ by a factor of two for just a one-centimeter snowfall (liquid water equivalent of approximately 1 mm). It is likely that, for typical rain and snow event the removal of atmospheric aerosol particles by snow is more effective than removal by rain for equivalent precipitation amounts, although a firm conclusion requires much more evidence.

scholarly journals Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds

2014 ◽  
Vol 14 (21) ◽  
pp. 28845-28883
Author(s):  
N. S. Umo ◽  
B. J. Murray ◽  
M. T. Baeza-Romero ◽  
J. M. Jones ◽  
A. R. Lea-Langton ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Coal Fly Ash ◽  
Aerosol Particles ◽  
Bottom Ash ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Dust Particles ◽  
Cloud Properties ◽  
Mixed Phase Clouds ◽  
The Impact

Abstract. Ice nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice nucleating particles, but the ice nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

scholarly journals Best practices for precipitation sample storage for offline studies of ice nucleation

2020 ◽  
Author(s):  
Charlotte M. Beall ◽  
Dolan Lucero ◽  
Thomas C. Hill ◽  
Paul J. DeMott ◽  
M. Dale Stokes ◽  
...  
Keyword(s):  
Room Temperature ◽  
Storage Time ◽  
Ice Nucleation ◽  
Correction Factors ◽  
Ice Crystal ◽  
Phase Partitioning ◽  
Cloud Properties ◽  
Precipitation Sample ◽  
Order Of Magnitude ◽  
La Jolla

Abstract. Ice nucleating particles (INPs) are efficiently removed from clouds through precipitation, a convenience of nature for the study of these very rare particles that influence multiple climate-relevant cloud properties including ice crystal concentrations, size distributions, and phase-partitioning processes. INPs suspended in precipitation can be used to estimate in-cloud INP concentrations and to infer their original composition. Offline droplet assays are commonly used to measure INP concentrations in precipitation samples. Heat and filtration treatments are also used to probe INP composition and size ranges. Many previous studies report storing samples prior to INP analyses, but little is known about the effects of storage on INP concentration or their sensitivity to treatments. Here, through a study of 15 precipitation samples collected at a coastal location in La Jolla, CA, USA, we found significant changes caused by storage to concentrations of INPs with warm to moderate freezing temperatures (−7 to −19 ºC). We compared four conditions: 1.) storage at room temperature (+21–23 ºC), 2.) storage at +4 ºC 3.) storage at −20 ºC, and 4.) flash freezing samples with liquid nitrogen prior to storage at −20 ºC. Results demonstrate that storage can lead to both enhancements and losses of greater than one order of magnitude, with non-heat-labile INPs being generally less sensitive to storage regime, but significant losses of INPs smaller than 0.45 μm in all tested storage protocols. No correlation was found between total storage time (1–166 days) and changes in INP concentration. We provide the following recommendations for preservation of precipitation samples from coastal environments intended for INP analysis: that samples be stored at −20 ºC to minimize storage artifacts, that changes due to storage are likely and an additional uncertainty in INP concentrations, and that filtration treatments be applied only to fresh samples. Average INP losses of 72 %, 42 %, 25 % and 32 % were observed for untreated samples stored using the room temperature, +4 ºC, −20 ºC, and flash frozen protocols, respectively. Finally, correction factors are provided so that INP measurements obtained from stored samples may be used to estimate concentrations in fresh samples.

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 Review and uncertainty assessment of size-resolved scavenging coefficient formulations for below-cloud snow scavenging of atmospheric aerosols

2013 ◽  
Vol 13 (19) ◽  
pp. 10005-10025 ◽  
Author(s):  
L. Zhang ◽  
X. Wang ◽  
M. D. Moran ◽  
J. Feng
Keyword(s):  
Atmospheric Aerosols ◽  
Atmospheric Aerosol ◽  
Collection Efficiency ◽  
Aerosol Particles ◽  
Empirical Formulas ◽  
Cross Sectional ◽  
Atmospheric Aerosol Particles ◽  
Order Of Magnitude ◽  
Snow Particle ◽  
Scavenging Coefficient

Abstract. Theoretical parameterizations for the size-resolved scavenging coefficient for atmospheric aerosol particles scavenged by snow (Λsnow) need assumptions regarding (i) snow particle–aerosol particle collection efficiency E, (ii) snow-particle size distribution N(Dp), (iii) snow-particle terminal velocity VD, and (iv) snow-particle cross-sectional area A. Existing formulas for these parameters are reviewed in the present study, and uncertainties in Λsnow caused by various combinations of these parameters are assessed. Different formulations of E can cause uncertainties in Λsnow of more than one order of magnitude for all aerosol sizes for typical snowfall intensities. E is the largest source of uncertainty among all the input parameters, similar to rain scavenging of atmospheric aerosols (Λrain) as was found in a previous study by Wang et al. (2010). However, other parameters can also cause significant uncertainties in Λsnow, and the uncertainties from these parameters are much larger than for Λrain. Specifically, different N(Dp) formulations can cause one-order-of-magnitude uncertainties in Λsnow for all aerosol sizes, as is also the case for a combination of uncertainties from both VD and A. Assumptions about dominant snow-particle shape (and thus different VD and A) will cause an uncertainty of up to one order of magnitude in the calculated scavenging coefficient. In comparison, uncertainties in Λrain from N(Dp) are smaller than a factor of 5, and those from VD are smaller than a factor of 2. As expected, Λsnow estimated from empirical formulas generated from field measurements falls in the upper range of, or is higher than, the theoretically estimated values, which can be explained by additional processes/mechanisms that influence field-derived Λsnow but that are not considered in the theoretical Λsnow formulas. Predicted aerosol concentrations obtained by using upper range vs. lower range of Λsnow values (a difference of around two orders of magnitude in Λsnow) can differ by a factor of 2 for just a one-centimetre snowfall (liquid water equivalent of approximately 1 mm). Based on the median and upper range of theoretically generated Λsnow and Λsnow values, it is likely that, for typical rain and snow events, the removal of atmospheric aerosol particles by snow is more effective than removal by rain for equivalent precipitation amounts, although a firm conclusion requires much more evidence.

scholarly journals Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds

2015 ◽  
Vol 15 (9) ◽  
pp. 5195-5210 ◽  
Author(s):  
N. S. Umo ◽  
B. J. Murray ◽  
M. T. Baeza-Romero ◽  
J. M. Jones ◽  
A. R. Lea-Langton ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Coal Fly Ash ◽  
Aerosol Particles ◽  
Bottom Ash ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Dust Particles ◽  
Cloud Properties ◽  
Mixed Phase Clouds ◽  
The Impact

Abstract. Ice-nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice-nucleating particles, but the ice-nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

scholarly journals Ion-induced nucleation of pure biogenic particles

Nature ◽  
2016 ◽  
Vol 533 (7604) ◽  
pp. 521-526 ◽  
Author(s):  
Jasper Kirkby ◽  
Jonathan Duplissy ◽  
Kamalika Sengupta ◽  
Carla Frege ◽  
Hamish Gordon ◽  
...  
Keyword(s):  
Sulfuric Acid ◽  
Atmospheric Aerosols ◽  
Radiative Forcing ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Particle Formation ◽  
Galactic Cosmic Rays ◽  
Binding Energies ◽  
Minor Role ◽  
Atmospheric Conditions

Abstract Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood1. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours2. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere3,4, and that ions have a relatively minor role5. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded6,7. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.

scholarly journals Characterization of individual ice residual particles by the single droplet freezing method: a case study in the Asian dust outflow region

2018 ◽  
Vol 18 (3) ◽  
pp. 1785-1804 ◽  
Author(s):  
Ayumi Iwata ◽  
Atsushi Matsuki
Keyword(s):  
Atmospheric Aerosols ◽  
Mineral Dust ◽  
Aerosol Particles ◽  
Ice Nucleation ◽  
Asian Dust ◽  
Particle Mixing ◽  
Active Particles ◽  
Nucleation Activity ◽  
Mixing States ◽  
Ice Nucleation Activity

Abstract. In order to better characterize ice nucleating (IN) aerosol particles in the atmosphere, we investigated the chemical composition, mixing state, and morphology of atmospheric aerosols that nucleate ice under conditions relevant for mixed-phase clouds. Five standard mineral dust samples (quartz, K-feldspar, Na-feldspar, Arizona test dust, and Asian dust source particles) were compared with actual aerosol particles collected from the west coast of Japan (the city of Kanazawa) during Asian dust events in February and April 2016. Following droplet activation by particles deposited on a hydrophobic Si (silicon) wafer substrate under supersaturated air, individual IN particles were located using an optical microscope by gradually cooling the temperature to −30 ∘C. For the aerosol samples, both the IN active particles and non-active particles were analyzed individually by atomic force microscopy (AFM), micro-Raman spectroscopy, and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Heterogeneous ice nucleation in all standard mineral dust samples tested in this study was observed at consistently higher temperatures (e.g., −22.2 to −24.2 ∘C with K-feldspar) than the homogeneous freezing temperature (−36.5 ∘C). Meanwhile, most of the IN active atmospheric particles formed ice below −28 ∘C, i.e., at lower temperatures than the standard mineral dust samples of pure components. The most abundant IN active particles above −30 ∘C were predominantly irregular solid particles that showed clay mineral characteristics (or mixtures of several mineral components). Other than clay, Ca-rich particles internally mixed with other components, such as sulfate, were also regarded as IN active particle types. Moreover, sea salt particles were predominantly found in the non-active fraction, and internal mixing with sea salt clearly acted as a significant inhibiting agent for the ice nucleation activity of mineral dust particles. Also, relatively pure or fresh calcite, Ca(NO3)2, and (NH4)2SO4 particles were more often found in the non-active fraction. In this study, we demonstrated the capability of the combined single droplet freezing method and thorough individual particle analysis to characterize the ice nucleation activity of atmospheric aerosols. We also found that dramatic changes in the particle mixing states during long-range transport had a complex effect on the ice nucleation activity of the host aerosol particles. A case study in the Asian dust outflow region highlighted the need to consider particle mixing states, which can dramatically influence ice nucleation activity.

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