APS Response to Nonspherical Particles and Experimental Determination of Dynamic Shape Factor

Brockmann, J.E.; Rader, Daniel J.

doi:10.1080/02786829008959434

Cited by 61 publications

(46 citation statements)

References 20 publications

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“…χ relates the mobility equivalent diameter of a particle to its mass equivalent diameter (Brockmann and Rader, 1990;Kelly and McMurry, 1992):…”

Section: Particle Shape Factorsmentioning

confidence: 99%

“…For compact spherical and cubic particles the dynamic shape factors are χ sphere =1.00 and χ cube =1.08, respectively. For agglomerates and irregularly shaped particles χ increases to values of 2 and more (Hinds, 1999;Brockmann and Rader, 1990;Willeke and Baron, 1993;Krämer et al, 2001). χ can be split into a component κ which describes the shape of the particle envelope and a component δ which is related to the particle porosity and allows the calculation of the void fraction inside the particle envelope, f (Brockmann and Rader, 1990):…”

Section: Particle Shape Factorsmentioning

confidence: 99%

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Interaction of aerosol particles composed of protein and saltswith water vapor: hygroscopic growth and microstructural rearrangement

Mikhailov

Vlasenko²,

Nießner³

et al. 2004

Atmos. Chem. Phys.

225

162

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Abstract. The interaction of aerosol particles composed of the protein bovine serum albumin (BSA) and the inorganic salts sodium chloride and ammonium nitrate with water vapor has been investigated by hygroscopicity tandem differential mobility analyzer (H-TDMA) experiments complemented by transmission electron microscopy (TEM) and Köhler theory calculations (100-300 nm particle size range, 298 K, 960 hPa). BSA was chosen as a well-defined model substance for proteins and other macromolecular compounds, which constitute a large fraction of the water-soluble organic component of air particulate matter.Pure BSA particles exhibited deliquescence and efflorescence transitions at ∼35% relative humidity (RH ) and a hygroscopic diameter increase by up to ∼10% at 95% RH in good agreement with model calculations based on a simple parameterisation of the osmotic coefficient. Pure NaCl particles were converted from near-cubic to near-spherical shape upon interaction with water vapor at relative humidities below the deliquescence threshold (partial surface dissolution and recrystallisation), and the diameters of pure NH 4 NO 3 particles decreased by up to 10% due to chemical decomposition and evaporation.Mixed NaCl-BSA and NH 4 NO 3 -BSA particles interacting with water vapor exhibited mobility equivalent diameter reductions of up to 20%, depending on particle generation, conditioning, size, and chemical composition (BSA dry mass fraction 10-90%). These observations can be explained by formation of porous agglomerates (envelope void fractions up to 50%) due to ion-protein interactions and electric charge effects on the one hand, and by compaction of the agglomerate structure due to capillary condensation effects on the other. The size of NH 4 NO 3 -BSA particles was apparCorrespondence to: U. Pöschl (ulrich.poeschl@ch.tum.de) ently also influenced by volatilisation of NH 4 NO 3 , but not as much as for pure salt particles, i.e. the protein inhibited the decomposition of NH 4 NO 3 or the evaporation of the decomposition products NH 3 and HNO 3 . The efflorescence threshold of NaCl-BSA particles decreased with increasing BSA dry mass fraction, i.e. the protein inhibited the formation of salt crystals and enhanced the stability of supersaturated solution droplets.The H-TDMA and TEM results indicate that the protein was enriched at the surface of the mixed particles and formed an envelope, which inhibits the access of water vapor to the particle core and leads to kinetic limitations of hygroscopic growth, phase transitions, and microstructural rearrangement processes.The Köhler theory calculations performed with different types of models demonstrate that the hygroscopic growth of particles composed of inorganic salts and proteins can be efficiently described with a simple volume additivity approach, provided that the correct dry solute mass equivalent diameter and composition are known. A parameterisation for the osmotic coefficient of macromolecular substances has been derived from an osmotic pressure virial equation. For its ...

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“…χ relates the mobility equivalent diameter of a particle to its mass equivalent diameter (Brockmann and Rader, 1990;Kelly and McMurry, 1992):…”

Section: Particle Shape Factorsmentioning

confidence: 99%

Section: Particle Shape Factorsmentioning

confidence: 99%

Interaction of aerosol particles composed of protein and saltswith water vapor: hygroscopic growth and microstructural rearrangement

Mikhailov

Vlasenko²,

Nießner³

et al. 2004

Atmos. Chem. Phys.

225

162

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“…Non-Stokesian behavior accounts for the experimental observation that two spherical particles of the same aerodynamic diameter can give different APS responses if their densities differ (Wilson and Liu, 1980;Baron, 1986;Ananth and Wilson, 1988). John (1987, 1989) have developed a method to correct the APS response for particle-density and slip effects for spherical particles; Brockmann and Rader (1990) have extended this method to nonspherical particles. Presented here is a method whereby a reference calibration obtained at one set of conditions may be applied at different ambient conditions and APS flow rates, and with different gases.…”

Section: Introductionmentioning

confidence: 99%

A Method To Employ the Aerodynamic Particle Sizer Factory Calibration Under Different Operating Conditions

Rader

Brockmann

Ceman

et al. 1990

Aerosol Science and Technology

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The dimensionless aerodynamic particle sizer (APS) response function (normalized particle velocity against particle Stokes number) first reported by Chen et al. (1985) is explored for much larger solid particles (diameters to 35 pm) over a similar range of instrument pressures (624-740 mm Hg) and flow rates (4.2-6.0 L/min). An essentially unique response function is found for low and intermediate Stokes numbers under a variety of operating conditions, including the use of argon as the carrier gas. For large particles, however, non-Stokesian drag effects introduce systematic differences among calibration sets so that a unique response function no longer applies. The largest differences are observed between calibrations performed in air and argon, although even in this case the sizing error amounts to < 12% for a 20-pm polystyrene latex sphere. For intermediate Stokes numbers, a direct consequence of this work is that a reference calibration (channel number against Stokes number) can be used under different ambient conditions by setting the APS to operate at the same nozzle velocity as used in the reference calibration. With the single-velocity method, the factory-supplied calibration relating channel number to aerodynamic diameter can be used for air over a reasonable range of ambient temperatures and pressures. The same calibration can be used with an argon carrier gas provided that the aerodynamic diameters reported by the APS software are adjusted by the square root of the gas viscosity ratio. For the singlevelocity mode of operation, a generalization of a correction proposed by John (1987, 1989) can be made and is shown to reduce by one half the sizing error introduced by non-Stokesian drag.

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“…To check the model of Brockmann and Rader (1990) measurements of the nanoparticle agglomerate velocity were made by LDA at a chamber pressure of 7.4 kPa in the impacting jet. To evaluate the model we compared the measured velocities to the ones predicted by the model.…”

Section: Comparison Of Measured and Predicted Velocities At 74 Kpamentioning

confidence: 99%

“…free jet and in the stagnation region near an impaction plate at pressures of 7.4 and 1.8 kPa (74 and 18 mbar). The data are used to fit an equation of motion based on the model by Brockmann and Rader (1990) for particles moving on the central axis of a radially symmetric jet. The model was finally used to predict the impaction velocity.…”

Section: Introductionmentioning

confidence: 99%

First LDA Measurements of Nanoparticle Velocities in a Low-Pressure Impacting Jet

Reuter-Hack

Weber

Rösler

et al. 2007

Aerosol Science and Technology

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The velocity of nanoparticle agglomerates and 1 μm latex spheres approaching an impaction surface from a free gas jet was measured by LDA at pressures of 7.4 and 1.8 kPa, respectively. The "aerodynamically transparent" carbon nano-agglomerates gave sufficient LDA signal while the drag force was dominated by the size of the individual primary particles (diameter about 11 nm). The particle velocity as a function of distance from the impaction plate was also modelled on the basis of a CFD simulation of the flow field and subsequent numerical integration of the equation of motion with the slip correction factor as an adjustable parameter.For a pressure of 7.4 kPa the measured and calculated velocities agreed very well, when using the Stokes formula with classical parameters for the slip correction. Surprisingly however, at 1.8 kPa the effective drag on the nanoparticles was lower than predicted by a factor of 17 and on the 1 μm latex sphere by a factor of 6, respectively. The physical reason for this reduction of the drag is not known so far. The predicted particle impact velocity at 1.8 kPa was 54% of the maximum gas velocity. This factor is much lower than the often used factor of 0.85 derived by Marple.

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APS Response to Nonspherical Particles and Experimental Determination of Dynamic Shape Factor

Cited by 61 publications

References 20 publications

Interaction of aerosol particles composed of protein and saltswith water vapor: hygroscopic growth and microstructural rearrangement

Interaction of aerosol particles composed of protein and saltswith water vapor: hygroscopic growth and microstructural rearrangement

A Method To Employ the Aerodynamic Particle Sizer Factory Calibration Under Different Operating Conditions

First LDA Measurements of Nanoparticle Velocities in a Low-Pressure Impacting Jet

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