scholarly journals Enhanced soot particle ice nucleation ability induced by aggregate compaction and densification

2021 ◽  
Author(s):  
Kunfeng Gao ◽  
Franz Friebel ◽  
Chong-Wen Zhou ◽  
Zamin A. Kanji
Keyword(s):  
Soot Particle ◽  
Aggregate Size ◽  
Ice Nucleation ◽  
Cirrus Clouds ◽  
Morphological Properties ◽  
Cloud Formation ◽  
Dynamic Vapor Sorption ◽  
Soot Particles ◽  
Soot Aggregate ◽  
Aggregate Morphology

Abstract. Soot particles, acting as ice nucleating particles (INPs), can contribute to cirrus cloud formation which has an important influence on climate. Aviation activities emitting soot particles in the upper troposphere can potentially impact ice nucleation (IN) in cirrus clouds. Pore condensation and freezing (PCF) is an important ice formation pathway for soot particles in the cirrus regime, which requires the soot INP to have specific morphological properties, i.e. mesopore structures. In this study, the morphology and pore size distribution of two kinds of soot samples were modified by a physical agitation method without any chemical modification, by which more compacted soot sample aggregates could be produced compared to the unmodified sample. The IN activities of both fresh and compacted soot particles with different sizes, 60, 100, 200 and 400 nm, were systematically tested by the Horizontal Ice Nucleation Chamber (HINC) under mixed-phase and cirrus clouds relevant temperatures (T). Our results show that soot particles are unable to form ice crystals at T > 235 K (homogeneous nucleation temperature, HNT) but IN was observed for compacted and larger size soot aggregates (> 200 nm) well below homogeneous freezing relative humidity (RHhom) at T < HNT, demonstrating PCF as the dominating mechanism for soot IN. We also observed that mechanically compacted soot particles can reach a higher particle activation fraction (AF) value for the same T and RH condition, compared to the same aggregate size fresh soot particles. The results also reveal a clear size dependence for the IN activity of soot particles with the same agitation degree, showing that compacted soot particles with large sizes (200 and 400 nm) are more active INPs and can convey the single importance of soot aggregate morphology for the IN ability. In order to understand the role of soot aggregate morphology for its IN activity, both fresh and compacted soot samples were characterized systematically using particle mass and size measurements, comparisons from TEM (transmission electron microscopy) images, soot porosity characteristics from argon (Ar) and nitrogen (N2) physisorption measurements, as well as soot-water interaction results from DVS (dynamic vapor sorption) measurements. Considering the soot particle physical properties along with its IN activities, the enhanced IN abilities of compacted soot particles are attributed to decreasing mesopore width and increasing mesopore occurrence probability due to the compaction process.

Enhanced soot particle ice nucleation ability induced by aggregate compaction

2021 ◽  
Author(s):  
Kunfeng Gao ◽  
Chong-Wen Zhou ◽  
Zamin Kanji
Keyword(s):  
Pore Size ◽  
Soot Particle ◽  
Preliminary Evidence ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Dynamic Vapor Sorption ◽  
Soot Particles ◽  
Formation Pathway ◽  
Soot Aggregate

&lt;p&gt;Cirrus clouds have an important influence on the climate since the ice crystal size, concentration and distribution of the clouds determine their radiation properties and effects in the atmosphere. Aviation activities in the high troposphere impact cirrus cloud formation indirectly and significantly, due to aviation contrail evolution and aviation soot particles acting as potential ice nucleating particles (INPs). Soot particles have varying ice nucleation (IN) abilities. In cirrus cloud formation conditions, pore condensation and freezing (PCF) is an important ice formation pathway for soot particles, which requires the particle to have appropriate morphology properties and mesoporous structures. In this study, the morphology and pore size of two kinds of soot were changed by a physical agitation method without any chemical modification. The IN activities of both fresh and agitated soot particles with aggregate sizes, 60, 100, 200 and 400 nm, were tested by the Horizontal Ice Nucleation Chamber (HINC) under mixed phase and cirrus cloud conditions.&lt;/p&gt;&lt;p&gt;In general, the IN results show clear size dependence for particles with the same agitation degree both tested soot samples at all tested temperatures (&lt;em&gt;T&lt;/em&gt;) from 218 K to 243 K with a step of 5 K. In addition, all soot particles do not form ice at &lt;em&gt;T &lt;/em&gt;&gt; 235 K (homogeneous nucleation temperature, HNT) but ice nucleation was observed well below homogeneous freezing relative humidity (&lt;em&gt;RH&lt;/em&gt;) for &lt;em&gt;T&lt;/em&gt; &lt; HNT, suggesting PCF as the dominating mechanism rather than deposition nucleation. Furthermore, there are significant differences between agitated and fresh soot particles for both soot samples studied. We observed that all agitated soot particles reach a higher particle activation fraction (&lt;em&gt;AF&lt;/em&gt;) value at the same &lt;em&gt;T&lt;/em&gt; and &lt;em&gt;RH&lt;/em&gt; condition, compared to the same size fresh soot particles. Moreover, 200 and 400 nm agitated soot particles require much lower ice saturation values to reach &lt;em&gt;AF&lt;/em&gt; = 0.001 than their fresh counterparts. The enhanced IN abilities of agitated soot particles are attributed to soot aggregate structure compaction thus increasing mesopore occurrence probability induced by physical agitation. Preliminary evidence obtained from the mass measurements of the single aggregates show that agitated soot particles are more dense than fresh soot particles of the same size. Furthermore, soot aggregate morphology comparisons from HR-TEM (high resolution transmission electron microscopy) images, soot-water interaction ability results from DVS (dynamic vapor sorption) tests and micro-pore size distribution results from argon desorption tests will be used to explain the soot particle IN ability promotion induced by compaction.&lt;/p&gt;

scholarly journals Ice nucleation activities of soot particles internally mixed with sulphuric acid at cirrus cloud conditions

2021 ◽  
Author(s):  
Kunfeng Gao ◽  
Chong-Wen Zhou ◽  
Eszter J. Barthazy Meier ◽  
Zamin A. Kanji
Keyword(s):  
Electron Microscopy ◽  
Sulphuric Acid ◽  
Soot Particle ◽  
Particle Surface ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Scanning Mobility Particle Sizer ◽  
Soot Particles ◽  
Two Samples

Abstract. Soot particles are important candidates for ice nucleating particles (INPs) in cirrus cloud formation which is known to exert a warming effect on climate. Bare soot particles, generally hydrophobic and fractal, mainly exist near emission sources. Coated or internally mixed soot particles are more abundant in the atmosphere and have a higher probability to impact cloud formation and climate. However, the ice nucleation ability of coated soot particles is not as well understood as that of freshly produced soot particles. In this study, two samples, a propane (C3H8) flame soot and a commercial carbon black were coated with varying wt % of sulphuric acid (H2SO4). The ratio of coating material mass to the mass of bare soot particle was controlled and progressively increased from less than 5 wt % to over 100 wt %. Both bare and coated soot particle ice nucleation activities were investigated with a continuous flow diffusion chamber operated at mixed-phase and cirrus cloud conditions. The mobility size and mass distribution of size selected soot particles with/without H2SO4 coating were measured by a scanning mobility particle sizer (SMPS) and a centrifugal particle mass analyser (CPMA) running in parallel. The mixing state and morphology of soot particles were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition, the evidence for the presence of H2SO4 on coated soot particle surface is shown by Energy Dispersive X-ray spectroscopy (EDX). Our study demonstrates that H2SO4 coatings suppress the ice nucleation activity of soot particles to varying degrees depending on the coating thickness, but in a non-linear fashion. Thin coatings causing pore filling in the soot-aggregate inhibits pore condensation and freezing (PCF). Thick coatings promote particle ice activation via droplet homogeneous freezing. Overall, our findings reveal that H2SO4 coatings will suppress soot particle ice nucleation abilities in the cirrus cloud regime, having implications for the fate of soot particles with respect to cloud formation in the upper troposphere.

scholarly journals Condensed-phase biogenic–anthropogenic interactions with implications for cold cloud formation

2017 ◽  
Vol 200 ◽  
pp. 165-194 ◽  
Author(s):  
Joseph C. Charnawskas ◽  
Peter A. Alpert ◽  
Andrew T. Lambe ◽  
Thomas Berkemeier ◽  
Rachel E. O’Brien ◽  
...  
Keyword(s):  
Freezing Temperature ◽  
Organic Aerosol ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Cloud Formation ◽  
Fossil Fuel Combustion ◽  
Soot Particles ◽  
Ice Nuclei ◽  
Deliquescence Relative Humidity ◽  
Homogeneous Freezing

Anthropogenic and biogenic gas emissions contribute to the formation of secondary organic aerosol (SOA). When present, soot particles from fossil fuel combustion can acquire a coating of SOA. We investigate SOA–soot biogenic–anthropogenic interactions and their impact on ice nucleation in relation to the particles’ organic phase state. SOA particles were generated from the OH oxidation of naphthalene, α-pinene, longifolene, or isoprene, with or without the presence of sulfate or soot particles. Corresponding particle glass transition (Tg) and full deliquescence relative humidity (FDRH) were estimated using a numerical diffusion model. Longifolene SOA particles are solid-like and all biogenic SOA sulfate mixtures exhibit a core–shell configuration (i.e.a sulfate-rich core coated with SOA). Biogenic SOA with or without sulfate formed ice at conditions expected for homogeneous ice nucleation, in agreement with respectiveTgand FDRH. α-pinene SOA coated soot particles nucleated ice above the homogeneous freezing temperature with soot acting as ice nuclei (IN). At lower temperatures the α-pinene SOA coating can be semisolid, inducing ice nucleation. Naphthalene SOA coated soot particles acted as ice nuclei above and below the homogeneous freezing limit, which can be explained by the presence of a highly viscous SOA phase. Our results suggest that biogenic SOA does not play a significant role in mixed-phase cloud formation and the presence of sulfate renders this even less likely. However, anthropogenic SOA may have an enhancing effect on cloud glaciation under mixed-phase and cirrus cloud conditions compared to biogenic SOA that dominate during pre-industrial times or in pristine areas.

Numerical Study of Temperature and Incandescence Intensity of Nanosecond Pulsed-Laser Heated Soot Particles at High Pressures

2005 ◽  
Author(s):  
Fengshan Liu ◽  
David R. Snelling ◽  
Gregory J. Smallwood
Keyword(s):  
Soot Particle ◽  
High Pressures ◽  
Particle Diameter ◽  
Aggregate Size ◽  
Primary Particle Diameter ◽  
Time Resolved ◽  
Soot Particles ◽  
Nanosecond Pulsed Laser ◽  
Primary Particles ◽  
Laser Heated

Histories of temperature and incandescence intensity of nanosecond pulsed-laser heated soot particles of polydispersed primary particles and aggregate sizes were calculated using an aggregate-based heat transfer model at pressures from 1 atm up to 50 atm. The local gas temperature, distributions of soot primary particle diameter and aggregate size assumed in the calculations were similar to those found in an atmospheric laminar diffusion flame. Relatively low laser fluences were considered to keep the peak particle temperatures below about 3400 K to ensure negligible soot particle sublimation. The shielding effect on the heat conduction between aggregated soot particles and the surrounding gas was accounted for based on results of direct simulation Monte Carlo calculations. After the laser pulse, the temperature of soot particles with larger primary particles or larger aggregates cools down slower than those with smaller primary particles or smaller aggregates due to smaller surface area-to-volume ratios. The effective temperature of soot particles in the laser probe volume was calculated based on the ratio of thermal radiation intensities of the soot particle ensemble at 400 and 780 nm. Due to the reduced mean free path of molecules with increasing pressure, the heat conduction between soot particles and the surrounding gas shifts from the free-molecular to the transition regime. Consequently, the rate of conduction heat loss from the soot particles increases significantly with pressure. The lifetime of laser-induced incandescence (LII) signal is significantly reduced as the pressure increases. At high pressures, the time resolved soot particle temperature is very sensitive to both the primary particle diameter and the aggregate size distributions, implying the time-resolved LII particle sizing techniques developed at atmospheric pressure lose their effectiveness at high pressures.

scholarly journals Effect of thermodenuding on the structure of nascent flame soot aggregates

2016 ◽  
Author(s):  
Janarjan Bhandari ◽  
Swarup China ◽  
Timothy Onasch ◽  
Lindsay Wolff ◽  
Andrew Lambe ◽  
...  
Keyword(s):  
Optical Properties ◽  
Ambient Air ◽  
Organic Coating ◽  
Index Of Refraction ◽  
Morphological Properties ◽  
Soot Particles ◽  
Internal Mixing ◽  
Soot Aggregate ◽  
Before And After ◽  
Particle Level

Abstract. The optical properties (light scattering and absorption) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with other material at the single particle level. For example, freshly emitted (nascent) soot particles can interact with other materials in the atmosphere, materials that can condense on soot and coat it. This coating can affect the soot optical properties by refracting light, or by changing the soot aggregate structure. A common approach to studying the effect of coating on soot optical properties is to measure absorption and scattering values in ambient air and then measure them again after removing the coating using a thermodenuder. In this approach, it is assumed that: 1) Most of the coating material is removed; 2) charred organic coating does not add to the refractory carbon; 3) oxidation of soot is negligible; and 4) the pre-existing core soot structure is left unaltered despite potential oxidation of the core at elevated temperature. In this study, we investigate the validity of the last assumption, by studying the effect of thermodenuding on the structure of nascent soot. To this end, we analyze the morphological properties of laboratory generated nascent soot, before and after thermodenuding. Our investigation shows that there is only minor restructuring of nascent soot by thermodenuding.

scholarly journals Ice nucleating particles over the Eastern Mediterranean measured by unmanned aircraft systems

2017 ◽  
Vol 17 (7) ◽  
pp. 4817-4835 ◽  
Author(s):  
Jann Schrod ◽  
Daniel Weber ◽  
Jaqueline Drücke ◽  
Christos Keleshis ◽  
Michael Pikridas ◽  
...  
Keyword(s):  
Transport Model ◽  
Eastern Mediterranean ◽  
Lower Troposphere ◽  
Ground Level ◽  
Ice Nucleation ◽  
Unmanned Aircraft ◽  
Unmanned Aircraft Systems ◽  
Saharan Dust ◽  
Cloud Formation ◽  
Aircraft Systems

Abstract. During an intensive field campaign on aerosol, clouds, and ice nucleation in the Eastern Mediterranean in April 2016, we measured the abundance of ice nucleating particles (INPs) in the lower troposphere from unmanned aircraft systems (UASs). Aerosol samples were collected by miniaturized electrostatic precipitators onboard the UASs at altitudes up to 2.5 km. The number of INPs in these samples, which are active in the deposition and condensation modes at temperatures from −20 to −30 °C, were analyzed immediately after collection on site using the ice nucleus counter FRIDGE (FRankfurt Ice nucleation Deposition freezinG Experiment). During the 1-month campaign, we encountered a series of Saharan dust plumes that traveled at several kilometers' altitude. Here we present INP data from 42 individual flights, together with aerosol number concentrations, observations of lidar backscattering, dust concentrations derived by the dust transport model DREAM (Dust Regional Atmospheric Model), and results from scanning electron microscopy. The effect of the dust plumes is reflected by the coincidence of INPs with the particulate matter (PM), the lidar signal, and the predicted dust mass of the model. This suggests that mineral dust or a constituent related to dust was a major contributor to the ice nucleating properties of the aerosol. Peak concentrations of above 100 INPs std L−1 were measured at −30 °C. The INP concentration in elevated plumes was on average a factor of 10 higher than at ground level. Since desert dust is transported for long distances over wide areas of the globe predominantly at several kilometers' altitude, we conclude that INP measurements at ground level may be of limited significance for the situation at the level of cloud formation.

scholarly journals Cirrus clouds in a global climate model with a statistical cirrus cloud scheme

2010 ◽  
Vol 10 (12) ◽  
pp. 5449-5474 ◽  
Author(s):  
M. Wang ◽  
J. E. Penner
Keyword(s):  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Cirrus Clouds ◽  
Cloud Formation ◽  
Cirrus Cloud ◽  
Ice Crystal ◽  
Homogeneous Freezing

Abstract. A statistical cirrus cloud scheme that accounts for mesoscale temperature perturbations is implemented in a coupled aerosol and atmospheric circulation model to better represent both subgrid-scale supersaturation and cloud formation. This new scheme treats the effects of aerosol on cloud formation and ice freezing in an improved manner, and both homogeneous freezing and heterogeneous freezing are included. The scheme is able to better simulate the observed probability distribution of relative humidity compared to the scheme that was implemented in an older version of the model. Heterogeneous ice nuclei (IN) are shown to decrease the frequency of occurrence of supersaturation, and improve the comparison with observations at 192 hPa. Homogeneous freezing alone can not reproduce observed ice crystal number concentrations at low temperatures (<205 K), but the addition of heterogeneous IN improves the comparison somewhat. Increases in heterogeneous IN affect both high level cirrus clouds and low level liquid clouds. Increases in cirrus clouds lead to a more cloudy and moist lower troposphere with less precipitation, effects which we associate with the decreased convective activity. The change in the net cloud forcing is not very sensitive to the change in ice crystal concentrations, but the change in the net radiative flux at the top of the atmosphere is still large because of changes in water vapor. Changes in the magnitude of the assumed mesoscale temperature perturbations by 25% alter the ice crystal number concentrations and the net radiative fluxes by an amount that is comparable to that from a factor of 10 change in the heterogeneous IN number concentrations. Further improvements on the representation of mesoscale temperature perturbations, heterogeneous IN and the competition between homogeneous freezing and heterogeneous freezing are needed.

scholarly journals Ice nucleation abilities of soot particles determined with the Horizontal Ice Nucleation Chamber

2018 ◽  
Vol 18 (18) ◽  
pp. 13363-13392 ◽  
Author(s):  
Fabian Mahrt ◽  
Claudia Marcolli ◽  
Robert O. David ◽  
Philippe Grönquist ◽  
Eszter J. Barthazy Meier ◽  
...  
Keyword(s):  
Particle Size ◽  
Water Saturation ◽  
Particle Surface ◽  
Water Vapor Sorption ◽  
Contact Angles ◽  
Ice Nucleation ◽  
Particle Surface Area ◽  
Soot Particles ◽  
Microphysical Properties ◽  
Homogeneous Freezing

Abstract. Ice nucleation by different types of soot particles is systematically investigated over the temperature range from 218 to 253 K relevant for both mixed-phase (MPCs) and cirrus clouds. Soot types were selected to represent a range of physicochemical properties associated with combustion particles. Their ice nucleation ability was determined as a function of particle size using relative humidity (RH) scans in the Horizontal Ice Nucleation Chamber (HINC). We complement our ice nucleation results by a suite of particle characterization measurements, including determination of particle surface area, fractal dimension, temperature-dependent mass loss (ML), water vapor sorption and inferred porosity measurements. Independent of particle size, all soot types reveal absence of ice nucleation below and at water saturation in the MPC regime (T>235 K). In the cirrus regime (T≤235 K), soot types show different freezing behavior depending on particle size and soot type, but the freezing is closely linked to the soot particle properties. Specifically, our results suggest that if soot aggregates contain mesopores (pore diameters of 2–50 nm) and have sufficiently low water–soot contact angles, they show ice nucleation activity and can contribute to ice formation in the cirrus regime at RH well below homogeneous freezing of solution droplets. We attribute the observed ice nucleation to a pore condensation and freezing (PCF) mechanism. Nevertheless, soot particles without cavities of the right size and/or too-high contact angles nucleate ice only at or well above the RH required for homogeneous freezing conditions of solution droplets. Thus, our results imply that soot particles able to nucleate ice via PCF could impact the microphysical properties of ice clouds.

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