scholarly journals Technical Note: The single particle soot photometer fails to detect PALAS soot nanoparticles

2012 ◽  
Vol 5 (4) ◽  
pp. 4905-4925 ◽  
Author(s):  
M. Gysel ◽  
M. Laborde ◽  
J. C. Corbin ◽  
A. A. Mensah ◽  
A. Keller ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Single Particle ◽  
Primary Particle ◽  
Particle Morphology ◽  
Counting Efficiency ◽  
Particle Mass ◽  
Effective Density ◽  
Soot Particles ◽  
Primary Particles ◽  
Small Primary

Abstract. The single particle soot photometer (SP2) uses laser-induced incandescence (LII) for the measurement of atmospheric black carbon (BC) particles. The BC mass concentration is obtained by combining quantitative detection of BC mass in single particles with a counting efficiency of 100% above its lower detection limit (LDL). It is commonly accepted that a particle must contain at least several tenths of femtograms BC in order to be detected by the SP2. Here we show the unexpected result that BC particles from a PALAS spark discharge soot generator remain undetected by the SP2, even if their BC mass, as independently determined with an aerosol particle mass analyser (APM), is clearly above the typical LDL of the SP2. Comparison of counting efficiency and effective density data of PALAS soot with flame generated soot (combustion aerosol standard burner, CAST), fullerene soot and carbon black particles (Cabot Regal 400R) reveals that particle morphology can affect the SP2's LDL. PALAS soot particles are fractal-like agglomerates of very small primary particles with a low fractal dimension, resulting in a very low effective density. Such loosely-packed particles behave like "the sum of individual primary particles" in the SP2's laser. Accordingly, the PALAS soot particles remain undetected as the SP2's laser intensity is insufficient to heat the primary particles to vaporisation because of their small size (primary particle diameter ~5–10 nm). It is not surprising that particle morphology can have an effect on the SP2's LDL, however, such a dramatic effect as reported here for PALAS soot was not expected. In conclusion, the SP2's LDL at a certain laser power depends on total BC mass per particle for compact particles with sufficiently high effective density. However, for fractal-like agglomerates of very small primary particles and low fractal dimension, the BC mass per primary particle determines the limit of detection, independent of the total particle mass. Consequently, care has to be taken when using the SP2 in applications dealing with loosely-packed particles that have very small primary particles as building blocks.

scholarly journals Technical Note: The single particle soot photometer fails to reliably detect PALAS soot nanoparticles

2012 ◽  
Vol 5 (12) ◽  
pp. 3099-3107 ◽  
Author(s):  
M. Gysel ◽  
M. Laborde ◽  
A. A. Mensah ◽  
J. C. Corbin ◽  
A. Keller ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Detection Limit ◽  
Particle Morphology ◽  
Counting Efficiency ◽  
Effective Density ◽  
Lower Detection Limit ◽  
Primary Particles ◽  
Lower Detection ◽  
Laser Induced Incandescence ◽  
Small Primary

Abstract. The single particle soot photometer (SP2) uses laser-induced incandescence (LII) for the measurement of atmospheric black carbon (BC) particles. The BC mass concentration is obtained by combining quantitative detection of BC mass in single particles with a counting efficiency of 100% above its lower detection limit. It is commonly accepted that a particle must contain at least several tenths of a femtogram BC in order to be detected by the SP2. Here we show the result that most BC particles from a PALAS spark discharge soot generator remain undetected by the SP2, even if their BC mass, as independently determined with an aerosol particle mass analyser (APM), is clearly above the typical lower detection limit of the SP2. Comparison of counting efficiency and effective density data of PALAS soot with flame generated soot (combustion aerosol standard burner, CAST), fullerene soot and carbon black particles (Cabot Regal 400R) reveals that particle morphology can affect the SP2's lower detection limit. PALAS soot particles are fractal-like agglomerates of very small primary particles with a low fractal dimension, resulting in a very low effective density. Such loosely packed particles behave like "the sum of individual primary particles" in the SP2's laser. Accordingly, most PALAS soot particles remain undetected as the SP2's laser intensity is insufficient to heat the primary particles to their vaporisation temperature because of their small size (Dpp ≈ 5–10 nm). Previous knowledge from pulsed laser-induced incandescence indicated that particle morphology might have an effect on the SP2's lower detection limit, however, an increase of the lower detection limit by a factor of ∼5–10, as reported here for PALAS soot, was not expected. In conclusion, the SP2's lower detection limit at a certain laser power depends primarily on the total BC mass per particle for compact particles with sufficiently high effective density. By contrast, the BC mass per primary particle mainly determines whether fractal-like particles with low fractal dimension and very small primary particles are detectable, while their total BC mass has only a minor influence. This effect shifts the lower detection limit to much higher BC mass, or makes them completely undetectable. Consequently, care has to be taken when using the SP2 in applications dealing with loosely packed particles that have very small primary particles as building blocks.

Fractal Characteristics of Soot Particles in Ethylene/Air inverse diffusion Flame

2014 ◽  
Vol 953-954 ◽  
pp. 1196-1200 ◽  
Author(s):  
Jian Yi Lv ◽  
Xin Cao ◽  
Cheng Long Meng
Keyword(s):  
Fractal Dimension ◽  
Primary Particle ◽  
Fractal Dimensions ◽  
Flame Height ◽  
Soot Particles ◽  
Transmission Electron ◽  
Primary Particles ◽  
Fractal Characteristics ◽  
Inverse Diffusion ◽  
Inverse Diffusion Flame

Soot is produced in incomplete combustion of fuels, it is harmful to human health and the environment. Sampling points were set along the flame height of different air-fuel ratios in ethylene/air IDF and samples were tested by transmission electron microscopy (TEM). MATLAB software was used to process TEM images, calculated the fractal dimensions of soot samples and analyzed the fractal features. With the increasing of air-fuel ratio, the soot fractal dimension decreases, the size and the number of primary particles included in aggregates increase. With the increasing of flame height, the fractal dimension value decreases, and the size of primary particle increases, the aggregating soot particles are united loose.

Measurement of aerosol effective density by single particle mass spectrometry

2015 ◽  
Vol 59 (2) ◽  
pp. 320-327 ◽  
Author(s):  
GuoHua Zhang ◽  
XinHui Bi ◽  
BingXue Han ◽  
Ning Qiu ◽  
ShouHui Dai ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Single Particle ◽  
Particle Mass ◽  
Effective Density ◽  
Single Particle Mass Spectrometry

Modelling Agglomeration and the Fluid Dynamic Behaviour of Agglomerates

2011 ◽  
Author(s):  
S. Stu¨bing ◽  
M. Dietzel ◽  
M. Sommerfeld
Keyword(s):  
Fractal Dimension ◽  
Drag Coefficient ◽  
Cross Section ◽  
Cross Sections ◽  
Primary Particle ◽  
Radius Of Gyration ◽  
Structure Model ◽  
Collision Model ◽  
Primary Particles ◽  
The Cross

For modeling agglomeration processes in the frame of the Lagrangian approach, where the particles are treated as point masses, an extended structure model was developed. This model provides not only information on the number of primary particles in the agglomerate, but also on the geometrical distension of the agglomerates. These are for example the interception diameter, the radius of gyration, the fractal dimension and the porosity of the agglomerate using the convex hull. The question however arises now, which is the proper agglomerate cross-section for the calculation of the drag force. In order to find an answer, the Lattice-Boltzmann-Method (LBM) was applied for simulating the flow about fixed agglomerates of different morphology and number of primary particles involved. From these simulations the drag coefficient was determined using different possible cross-sections of the agglomerate. Numerous simulations showed that the cross-section of the convex hull yields a drag coefficient which is almost independent on the structure of the agglomerate if they have the same cross-sectional area in flow direction. Using the cross-section of the volume equivalent sphere showed a very large scatter in the simulated drag coefficient. This information was accounted for in the Lagrangian agglomeration model. The basis of modeling particle collisions and possible agglomeration was the stochastic inter-particle collision model accounting for the impact efficiency. The possibility of particle sticking was based on a critical velocity determined from an energy balance which accounts for dissipation and the van der Waals adhesion. If the instantaneous relative velocity between the particles is smaller than this critical velocity agglomeration occurs. In order to allow the determination of the agglomerate structure reference vectors are stored between a reference particle and all other primary particles collected in the agglomerate. For describing the collision of a new primary particle with an agglomerate the collision model was extended in order to determine which primary particle in the agglomerate is the collision partner. For demonstrating the capabilities of the Lagrangian agglomerate structure model the dispersion and collision of small primary particles in a homogeneous isotropic turbulence was considered. From these calculations statistics on the properties of the agglomerates were made, e.g. number of primary particles, radius of gyration, porosity, sphericity and fractal dimension. Finally, the dispersion of particles in vertical grid turbulence was calculated by the Lagrangian approach. For one selected model agglomerate, dispersion calculations were performed with different possible characteristic cross-sections of the agglomerate. These calculations gave a deviation of the mean square dispersion of up to 20% after a dispersion time of 0.4 seconds for the different cross-sections. This demonstrates that a proper selection of the cross-section is essential for calculating agglomerate motion in turbulent flows.

scholarly journals Soot PCF: pore condensation and freezing framework for soot aggregates

2021 ◽  
Vol 21 (10) ◽  
pp. 7791-7843
Author(s):  
Claudia Marcolli ◽  
Fabian Mahrt ◽  
Bernd Kärcher
Keyword(s):  
Primary Particle ◽  
Capillary Condensation ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Soot Particles ◽  
Primary Particles ◽  
Pore Types ◽  
Pore Properties ◽  
New Framework

Abstract. Atmospheric ice formation in cirrus clouds is often initiated by aerosol particles that act as ice-nucleating particles. The aerosol–cloud interactions of soot and associated feedbacks remain uncertain, in part because a coherent understanding of the ice nucleation mechanism and activity of soot has not yet emerged. Here, we provide a new framework that predicts ice formation on soot particles via pore condensation and freezing (PCF) that, unlike previous approaches, considers soot particle properties, capturing their vastly different pore properties compared to other aerosol species such as mineral dust. During PCF, water is taken up into pores of the soot aggregates by capillary condensation. At cirrus temperatures, the pore water can freeze homogeneously and subsequently grow into a macroscopic ice crystal. In the soot-PCF framework presented here, the relative humidity conditions required for these steps are derived for different pore types as a function of temperature. The pore types considered here encompass n-membered ring pores that form between n individual spheres within the same layer of primary particles as well as pores in the form of inner cavities that form between two layers of primary particles. We treat soot primary particles as perfect spheres and use the contact angle between soot and water (θsw), the primary particle diameter (Dpp), and the degree of primary particle overlap (overlap coefficient, Cov) to characterize pore properties. We find that three-membered and four-membered ring pores are of the right size for PCF, assuming primary particle sizes typical of atmospheric soot particles. For these pore types, we derive equations that describe the conditions for all three steps of soot PCF, namely capillary condensation, ice nucleation, and ice growth. Since at typical cirrus conditions homogeneous ice nucleation can be considered immediate as soon as the water volume within the pore is large enough to host a critical ice embryo, soot PCF becomes limited by either capillary condensation or ice crystal growth. We use the soot-PCF framework to derive a new equation to parameterize ice formation on soot particles via PCF, based on soot properties that are routinely measured, including the primary particle size, overlap, and the fractal dimension. These properties, along with the number of primary particles making up an aggregate and the contact angle between water and soot, constrain the parameterization. Applying the new parameterization to previously reported laboratory data of ice formation on soot particles provides direct evidence that ice nucleation on soot aggregates takes place via PCF. We conclude that this new framework clarifies the ice formation mechanism on soot particles in cirrus conditions and provides a new perspective to represent ice formation on soot in climate models.

scholarly journals Soot-PCF: Pore condensation and freezing framework for soot aggregates

2020 ◽  
Author(s):  
Claudia Marcolli ◽  
Fabian Mahrt ◽  
Bernd Kärcher
Keyword(s):  
Primary Particle ◽  
Water Saturation ◽  
Capillary Condensation ◽  
Ice Nucleation ◽  
Membered Ring ◽  
Ice Formation ◽  
Soot Particles ◽  
Ice Growth ◽  
Primary Particles ◽  
Pore Types

Abstract. How ice crystals form in the troposphere strongly affects cirrus cloud properties. Atmospheric ice formation is often initiated by aerosol particles that act as ice nucleating particles. The aerosol-cloud interactions of soot and associated feedbacks remain uncertain, in part because a coherent understanding of the ice nucleation mechanism and activity of soot has not yet emerged. Here, we provide a new framework that predicts ice formation on soot particles via pore condensation and freezing (PCF) that, unlike previous approaches, considers soot particle properties capturing their vastly different pore properties compared to other aerosol species such as mineral dust. During PCF, water is taken up below water saturation into pores on soot aggregates by capillary condensation. At cirrus temperatures, pore water can freeze homogeneously and subsequently grow into a macroscopic ice crystal. In the soot-PCF framework presented here, the relative humidity conditions required for these steps are derived for different pore types as a function of temperature. The pore types considered here evolve from idealized stacking of equally sized primary particles, either in tetrahedral or cubic packing arrangements. Specifically, we encompass n-membered ring pores that form between n individual spheres within the same layer of primary particles as well as pores in the form of inner cavities that form between two layers of primary particles. We treat soot primary particles as perfect spheres and use the contact angle between soot and water (θsw), the primary particle diameter (Dpp) and the degree of primary particle overlap (overlap coefficient, Cov) to characterize soot pore properties. We find that n-membered ring pores are the dominant pore structures for soot-PCF, as they are common features of soot aggregates and have a suitable geometry for both, filling with water and growing ice below water saturation. We focus our analysis on three-membered and four-membered ring pores as they are of the right size for PCF assuming primary particle sizes typical for atmospheric soot particles. For these pore types, we derive equations that describe the conditions for all three steps of soot-PCF, namely capillary condensation, ice nucleation, and ice growth. Since at typical cirrus conditions homogeneous ice nucleation can be considered immediate as soon as the water volume within the pore is large enough to host a critical ice embryo, soot-PCF becomes either limited by capillary condensation or ice crystal growth. For instance, our results show that at typical cirrus temperatures of T = 220 K, three-membered ring pores formed between primary particles with θsw = 60°, Dpp = 20 nm, and Cov = 0.05 are ice growth limited, as the ice requires a relative humidity with respect to ice of RHi = 137 % to grow out of the pore, while a sufficient volume of pore water for ice nucleation has condensed already at RHi = 86 %. Conversely, four-membered ring pores with the same primary particle size and an overlap coefficient of Cov = 0.1 are capillary condensation limited as they require RHi = 129 % to gather enough water for ice nucleation, compared with only 124 % RHi, required for ice growth. We use the soot-PCF framework to derive a new equation to parameterize of ice formation on soot particles via PCF. This equation is based on soot properties that are routinely measured, including the primary particle size and overlap, and the fractal dimension. These properties, along with the number of primary particles making up an aggregate and the contact angle between water and soot, constrain the parameterization. Applying the new parameterization to previously reported laboratory data of ice formation on soot particles provides direct evidence that ice nucleation on soot aggregates takes place via PCF. We conclude that this new framework clarifies the ice formation mechanism on soot particles at cirrus conditions and provides a new perspective to represent ice formation on soot in climate models.

scholarly journals Size-resolved chemical composition, effective density, and optical properties of biomass burning particles

2016 ◽  
Author(s):  
Jinghao Zhai ◽  
Xiaohui Lu ◽  
Ling Li ◽  
Qi Zhang ◽  
Ci Zhang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Chemical Composition ◽  
Density Distribution ◽  
Biomass Burning ◽  
Single Particle ◽  
Particle Mass ◽  
Effective Density ◽  
Potassium Salts ◽  
Biomass Burning Aerosol ◽  
Biomass Burning Particles

Abstract. Biomass burning aerosol has important impact on the global radiative budget. A better understanding of the mixing state and chemical composition of biomass burning particles relative to their optical properties is the goal of a number of current studies. In this work, effective density, chemical composition, and optical properties of rice straw burning particles in the size range of 50–400 nm were measured using a suite of comprehensive methods. A Differential Mobility Analyzer (DMA)-Aerosol Particle Mass analyzer (APM)-Condensation Particle Counter (CPC) system offered detailed information on the effective density as well as mixing state of size-resolved particles. The effective density and chemical composition of individual particles were characterized with a DMA in-line with a Single Particle Aerosol Mass Spectrometer (SPAMS), simultaneously. The multiple modes observed in the size-resolved particle effective density distribution indicated size-dependent external mixing of black carbon (BC), organic carbon (OC) and potassium salts in particles. Particles of 50 nm had the smallest effective density (1.16 g/cm3), due to a relative large proportion of aggregate BC. The average effective densities of 100–400 nm particles ranged from 1.35–1.51 g/cm3 with OC and inorganic salts as dominant components. Both density distribution and single-particle mass spectrometry showed more complex mixing states in larger particles. Upon heating, the separation of the effective density distribution modes testified the existence of less volatile BC or soot and potassium salts. Size-resolved optical properties of biomass burning particles were measured by the Cavity Attenuated Phase Shift spectroscopy (CAPS, λ = 450 & 530 nm). The single scattering albedo (SSA) showed the lowest value for 50 nm particles (0.741 ± 0.007 & 0.889 ± 0.006) because of larger proportion of BC content. Brown carbon played an important role for the SSA of 100–400 nm particles. The Ångström absorption exponent (AAE) values for all particles were above 1.6, indicating the significant presence of brown carbon. Though freshly emitted, the light absorption enhancement (Eabs) was observed for particles larger than 200 nm. Concurrent measurements in our work provide a basis for discussing the physicochemical properties of biomass burning aerosol and its effects on global climate and atmospheric environment.

Characterization of Large Particles in Fumed Silica Based CMP Slurry

2010 ◽  
Vol 1249 ◽  
Author(s):  
W. Scott Rader ◽  
Timothy Holt ◽  
Kazusei Tamai
Keyword(s):  
Fumed Silica ◽  
Large Particle ◽  
Particle Morphology ◽  
Sedimentation Rates ◽  
Transmission Electron ◽  
Primary Particles ◽  
Large Particles ◽  
Small Primary ◽  
Morphological Differences

AbstractLarge particles in fumed silica dispersions were characterized by sedimentation, light scattering techniques, Transmission Electron Microscopy (TEM), and lacunarity. Applying centrifugation to fumed silica dispersions generated differences in sedimentation rates of large particles. The sedimentation rates of the large particles were affected by morphological differences and the particles remaining in the supernatant displayed buoyant behavior. The large particle morphology varied from branch like aggregates containing large primary particles to particles comprised of highly coalesced, tightly packed small primary particles. The results indicate the presence of different types of large particles in fumed silica dispersions to which conventional large particle characterization is unable to distinguish.

scholarly journals FLUCTUATIONS OF Xmax AND PRIMARY PARTICLE MASS COMPOSITION IN THE RANGE OF ENERGY 5 × 1017 - 3 × 1019EV BY YAKUTSK DATA

2005 ◽  
Vol 20 (29) ◽  
pp. 6894-6896 ◽  
Author(s):  
S. P. KNURENKO ◽  
A. A. IVANOV ◽  
V. A. KOLOSOV ◽  
Z. E. PETROV ◽  
I. YE. SLEPTSOV ◽  
...  
Keyword(s):  
Experimental Data ◽  
Primary Particle ◽  
Particle Mass ◽  
Mass Composition ◽  
Primary Particles ◽  
Recent Version

The experimental distributions of X max obtained with the Yakutsk EAS array at fixed energies of 5 × 1017, 1 × 1018 and 5 × 1018 eV are analysed. A recent version of the QGSJET model is used as a tool of our analysis. In the framework of this model, the most adequate mass composition of primary particles satisfying the experimental data on X max is selected.

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