Scanning Mobility Particle Sizing (SMPS) Key Factors for Accuracy

Welcome! 欢迎! 歓迎! 환영! Добро пожаловать!! व गत! Scanning Mobility Particle Sizing (SMPS) Key Factors for Accuracy This webinar will begin at: Greenwich Mean Time (GMT) Thursday, 1:00am Beijing, China 8:00am Tokyo, Japan 9:00am US CST 7:00pm (Wednesday Evening) Note: you need to join the webinar in two ways: over the phone (audio) and on the internet (visual). Ready-Access phone numbers: https://g8.cfer.com/g8.jsp?an=8005048071&ac=4902732&login=true link and information included with e-mail login information Kathy Erickson Product Specialist Particle Instruments April 20, 2011

Welcome! Willkommen! Bienvenue! Benvenuto! Recepción! Καλώς Ήρθατε! Добро пожаловать! Scanning Mobility Particle Sizing (SMPS) Key Factors for Accuracy This webinar will begin at: Greenwich Mean Time (GMT) Thursday, 2:00pm UK, London 2:00m Germany, Berlin 3:00pm India 6:30pm US CST 8:00am Note: you need to join the webinar in two ways: over the phone (audio) and on the internet (visual). Ready-Access phone numbers: https://g8.cfer.com/g8.jsp?an=8005048071&ac=4902732&login=true link and information included with e-mail login information Kathy Erickson Product Specialist Particle Instruments April 20, 2011

Welcome! 欢迎! Willkommen! 歓迎! Bienvenue! व गत! Scanning Mobility Particle Sizing (SMPS) Key Factors for Accuracy This webinar will begin at: Greenwich Mean Time (GMT) Thursday, 5:00pm US PST 9:00am US CST 11:00am US EST 12:00pm (just after noon) Germany, Berlin 6:00pm Kathy Erickson Product Specialist Particle Instruments April 20, 2011 Note: you need to join the webinar in two ways: over the phone (audio) and on the internet (visual). Ready-Access phone numbers: https://g8.cfer.com/g8.jsp?an=8005048071&ac=4902732&login=true link and information included with e-mail login information

Interactive Webinar Format 1. Connection Information: You need to join the webinar in two ways Audio: via telephone - phone numbers and link information included with e-mail login information Visual: via internet - link information included login information 2. Sound quality: For large groups, the sounds quality is much better if the conference is kept on mute. 3. Multi-media - Interactive chat: Please send questions via chat during and after the presentation. 4. Follow-up: e-mail including Adobe pdf file of presentation will be sent to registered attendees.

Electrical Mobility Sizing: Outline Introduction & Theory Key Factors for Accuracy 1. DMA voltage, flows & design 2. Charge Distribution 3. Efficiency curve of the CPC 4. DMA transfer function 5. Scan time 6. Parameters of working gas 7. Diffusion losses 8. Aggregate correction ISO 15900 ES + SMPS Closing Comments

Applications for Nanoparticle Sizing Particle Size: Critical Metric Nanomaterial R&D Inhalation Toxicology Indoor Air Quality Engine/Fuel Development Atmospheric Research Filter Efficiency Testing Manufacturing Process Control Emission Characterization

Milestones in Electrical Mobility Particle Sizing ~1900 Electrostatic classification of atmospheric aerosols 1921 Erickson first Differential Mobility Analyzer (DMA) 1957 Hewitt co-axial cylindrical DMA with unipolar charging 1966 Whitby & Clark Whitby Aerosol Analyzer (TSI 1967 first commercial system) 1983 TSI DMPS voltage stepping system 1990 Scanning concept devised by Wang & Flagan 1991 Used by NIST to size 60nm (Mulholland et al 1991) 1993 First commercial scanning sizing system Scanning Mobility Particle Sizer Spectrometer (SMPS) 2005 Duke Scientific (Vasilou) evaluated scanning SMPS to size 20 to 100nm PSL In all cases, the SMPS mean diameter fell within the uncertainty of the reference standard [TEM]. Note: surface techniques designed to image nanoparticles not designed for sizing accuracy. 2006 Used by NIST to size 60nm & 100nm SRM (Mulholland et al 2006) 2009 ISO Standard 15900:2009 Determination of particle size distribution Differential electrical mobility analysis for aerosol particles 2010 NIST Test Protocol Analysis of Gold Nanoparticles by Electrospray Differential Mobility Analysis (ES-DMA) [nanoparticle liquid colloids (sol)] 2009, 2007, TSI Incorporated

Reasons for Increased Interest in Electrical Mobility-based Sizing Discreet method: individual particles are counted and sized Large sample size No assumptions regarding size distribution Independent of optical properties of material (& liquid) 1 st principle technique: no size calibration necessary High resolution: ~±10% of particle size (or better at higher flow ratios) it affords an opportunity to monitor the quality of product particles in real time with size resolution that is unattainable in most other particle characterization technologies (Flagan 2008) Low uncertainty: ±3.5% (Mullholand et al 1991) Real-time: 16-300s Easy to use; does not require a trained technician

Colloids Suitable for Electrical Mobility Particle Sizing Colloids - a substance microscopically dispersed evenly throughout another substance Dispersed Phase Gas Liquid Solid Continuous Medium Gas None All gases are miscible Liquid aerosol Solid aerosol Liquid Foam Emulsion Sol Solid Solid Foam Gel Solid sol 2009, 2007, TSI Incorporated

Electrical Mobility Analysis Z p electrical mobility; ability of a charged particle to traverse an electric field ❶ ❷ ❸ ❹ F F F Z electric = viscous drag electric p n ee p Dpv = 3πµ C = Fviscous drag v npec = = E 3πµ D p Where: n p = number of charges per particle e = elementary unit of charge E = electric field strength µ = viscosity of gas D p = particle diameter C = Cunningham slip correction v = Velocity Second order function of particle size Electrical mobility: inversely proportional to particle size Assumptions Stoke s Regime (Re<1) Drag based on rigid sphere

Differential Mobility Analyzer (DMA) Classical Knutson & Whitby cylindrical DMA design (1975) Applied voltage determines electric field Laminar flow Particle free sheath air 4 balanced flows Monodisperse aerosol exiting DMA 2009, 2007, TSI Incorporated

Mobility Particle Sizing Z p v npec = = E 3πµ D p Aerosol Conditioner Differential Mobility Analyzer Classifier Particle Counter Produces a known charge distribution Selects particles according to electrical mobility particle size Counts size selected particles to build distribution Control hardware & software

Laminar Flow CPCs S P P S = Supersaturation Ratio P v = Vapor Pressure v saturation ( T) P saturation (T) = Saturation Vapor Pressure Fast Precise temperature control Low particle losses 2009, 2007, TSI Incorporated D kelvin d S M r L R T S D kelvin = ρ L 4δ SM RTlogS = Kelvin Diameter = Surface Tension of Working Fluid = Molecular Weight of Working Fluid = Density of Working Fluid = Gas Constant = Temperature = Supersaturation Ratio Assumption: particle material is readily wetted by but insoluble in the condensing vapor

Scanning Mobility Particle Sizer Polydisperse Aerosol SMPS Scanning Voltage DMA 1990 Wang & Flagan If voltage is exponentially ramped, all particles follow the same trajectory in the DMA The resolution (transfer function of the DMA) is identical to that of stepping systems 16 to 300s (or below?) Size Distribution DMA Selects Single Size Monodisperse Aerosol Concentration Counter Voltage/Diameter

SMPS: Key Factors for Accuracy True: 1 st Principle Device: No calibration required Also True: Data Inversion - Electrical Mobility to Particle Size 1. DMA voltage, flows & design 2. Charge distribution 3. Efficiency curve of the CPC 4. DMA transfer function 6. Scan time 7. Parameters of working gas 8. Diffusion losses 9. Aggregate correction 2009, 2007, TSI Incorporated

DMA Voltage & Flowrates Z p v npec = = E 3πµ D p Z p = [q 1/ 2(q + q t p 2πVL m r )]ln( r 2 1 ) Where: q t q m q p r 2 r 1 V L = total flowrate (sheath + poly) = monodisperse flowrate = polydisperse flowrate = outer electrode radius = inner electrode radius = voltage on center electrode = length between sample exit and aerosol inlet

Nano Differential Mobility Analyzer Designed in collaboration with the University of Duisburg and the University of MN Aim to improve nanometer size resolution Shortening effective length Eliminate flow and electric field non-uniformities Minimize diffusion broadening Increase transmission efficiency 1. Reduce particle losses due to diffusion 2. Reduce losses due to electrostatic forces DMA design governs Size range Ideal resolution (increased resolution <10nm results in decreased size range) Electric field & flow uniformities (manufacturing non-conformities can also affect this). 2009, 2007, TSI Incorporated

DMA Voltage & Flowrates Voltage 1) Reliable high voltage supply & electronics 2) Calibrated using NIST Traceable meters Flow 1) Laminar flow element 2) Re-circulating flow scheme to minimizes flow disturbances (decreased resolution) 3) NIST Traceable flow meters 4) Volumetric flow rate: atmospheric temperature & pressure adjustment. 5) Periodically check flow accuracy with independent volumetric flow meter.

Charges Per Particle Must know number of charges per particle Equilibrium Charge Distribution Z p = Particle Velocity Electric Field Strength = V E = nec 3πµD p Need to Generate Bi-polar Ions Note: Poor charging leads predominately to concentration inaccuracies. However, since charging is size dependent it leads to sizing inaccuracies as well. 2009, 2007, TSI Incorporated

Two Neutralizers Aerosol In - - Traditional Kr-85 gas + + - + + + - - - + - + + - Kr-85 gas sealed stainless-steel tube - + - + Aerosol Out Kr-85 facts Kr-85 inert gas sealed in air-tight stainless steel Never absorbed by the body In US classified as a non-biological health hazard In US no handling limitations for amount used in SMPS 10.4 year half life Beta-emitter Advanced Aerosol Neutralizer Soft X-ray Nonradioactive Comparable SMPS sizing No transportation restrictions Does not decay over time

Poor Charging: Soot Aerosol Generated aerosol is very highly charged High soot aerosol concentration and 1 neutralizer TSI model 3077: SMPS measurement shows that charge equilibrium was not reached Diluted soot aerosol and neutralizers TSI models 3077 and 3012 in series: Charge equilibrium was reached If the aerosol is highly charged & poorly neutralized (left hand side) large errors in size distribution and concentration.

Multiple Charges Fuch s Equilibrium Charge Distribution Percent of particles carrying n p elementary charge units D p (nm) -2-1 0 +1 +2 10 0 5.03 90.96 4.02 0 20 0.02 11.14 80.29 8.54 0.01 50 1.13 22.94 58.10 17.20 0.63 70 2.80 26.02 49.99 19.53 1.57 100 5.67 27.42 42.36 20.75 3.24 130 8.21 27.30 37.32 20.85 4.77 200 12.18 25.54 29.96 19.65 7.21 300 14.56 22.71 24.16 17.51 8.65 500 15.09 18.60 18.28 14.33 8.95 700 14.29 15.94 15.15 12.27 8.46 1000 12.86 13.33 12.36 10.24 7.59 FromA. Wiedensohler: An Approximation of the Bipolar Charge Distribution for Particles in the Submicron Size Range, Journal of Aerosol Science, Vol. 19, No. 3, pp. 387-389, 1988.

Multiple Charge Correction Useful for larger aerosols Must use impactor (physical size cut no larger multiple particles) Works best if impactor cut point is just to the right of complete distribution Too far to the right no effect Cut into size distribution will see notch in distribution Best to view distribution, and use if makes sense

Efficiency Curve of CPC CPC Efficiency Curve ing Efficiency % Counti 50% cut point ~ 2.5 nm Particle Diameter (nm) CPC Efficiency curves affected by: 1) Instrument to instrument variation 2) Working fluid 3) Carrier gas (Niida et al 1988) Sizing Accuracy: 1) Most applications, small CPC efficiency curve differences have very little effect on accuracy. 2) Nanoparticle applications can be sensitive to efficiency curves: large numbers of particles close to the lower detection limit. 3) Can generate custom efficiency curve to use in data inversion (Liu et al 2006).

DMA Transfer Function Transfer Function probability that an entering particle with a specific electrical mobility will have the correct trajectory to exit through the exit slit with the classified aerosol. (Knutson & Whitby 1975) Ideal Transfer Function Z p = q a qs Z p Where: q a = aerosol flowrate q s = sheath flowrate = set mobility Z p Concentration Electrical Mobility 9nm NDMA Transfer Function (Knutson & Whitby 1975) Particle Diameter D p (nm)

Effect of sheath:sample Flow Ratio on SMPS Transfer Function Tandom DMA Experimental Setup: Adjust flow ratio on DMA 1 MODEL 3480 + + DMA 1 DMA 2 ElectroSpray Aerosol Generator Electrospray Aerosol: No TDMA 10:1 sheath:sample Flow rate on DMA 1 2:1 Sheath:Sample Flow rate on DMA 1

Effect of Sheath:Sample Flow Ratio on Electrostatic Classifier Tandom DMA Experimental Setup: Adjust flow ratio on DMA 2 MODEL 3480 + + DMA 1 DMA 2 ElectroSpray Aerosol Generator 10:1 sheath:sample Flow rate on DMA 2 5:1 sheath:sample Flow rate on DMA 2 2:1 sheath:sample Flow rate on DMA 2

Diffusion Broadening Widens the transfer function for nanoparticles <100nm Reduces peak transmission efficiency More severe at lower voltages Significant for particles <20nm Stolzenberg (1998) created a model for the diffusionbroadened transfer function Shortening the effective length of the DMA & increasing the flowrate through the DMA: 1. reduces diffusion broadening 2. reduces the size range

Scan Time a) 300 s b) 16 s Electrospray Sucrose Aerosol

Scan Time Fast Scanning - CPC features 1) Laminar flow 2) Fast response 3) High aerosol flow rate/high concentration aerosol a) 300 s b) 16 s c) 16 s scan range 6.98 12 nm Electrospray Sucrose Aerosol Russell et al (1995) noted scan time effect : for very short scans, tails toward larger distributions; theorized result of turbulent mixing in plumbing between DMA & CPC & internal to CPC - primarily notable on older 3071A classifier platforms & CPCs.

Parameters of Working Gas Working gas sheath gas in the DMA. Note: If using a recirculating flow scheme, the sample carrier gas will eventually become the sheath gas. Z p = Particle Velocity Electric Field Strength = V E = nec 3πµD p µ and C both affected by working gas properties Cunningham Slip Coefficient C = ƒ(λ, D p ); λ = mean free path of working gas Empirical formula dependent on gas T & P In free molecular regime Kn>>1 (<10nm); C 1.7 Software Calculates µ & λ Classifier measures T&P of air Software calculates gas viscosity (µ) and mean free path (λ) for every sample (based on air)

Other Working Gases Gas Property Air N 2 Ar CO 2 He µ (10-4 g/cm-s) 1.82 1.75 2.2 1.47 1.95 λ (10-6 cm) 6.64 6.41 6.75 4.69 18.7 Flowmeters are calibrated with Air (must manually measure and control flow) Noble gases have breakdown voltages much lower than air: this will effectively reduce the upper end size range (Meek & Craggs 1978) Bipolar charge distribution differs can use extended Fuchs model (Wiedensohler 1991) CPC efficiencies differ in gases other than air (Ahn 1990) Karg et al (1992), Schmid (2002) investigated DMA accuracy in N2, Ar, CO2 & He and generally concluded no fundamental effect of gas type

Diffusion Losses Diffusion is a stronger than gravitational forces for particle <100nm 1.0 Circular Tube Penetration Efficiency Diffusion losses are size dependent. Penetration 0.9 0.8 0.7 0.6 0.5 0.4 0.3 Gormley and Kennedy (1949) derived an equation for circular tube penetration efficiency. 0.2 0.1 0.0 D = Diffusion coefficient; D = ƒ(t, Gas type, d p) ) L = Length of tube Q = Volumetric flow rate 0.00001 0.0001 0.001 DL 0.01 0.1 1 Q

Diffusion Losses Diffusion losses with: 1) Increasing tubing length 2) Decreasing particle diameter 3) Increasing temperature SMPS Diffusion loss: 1) Sampling scheme 2) System losses through Controller platform DMA CPC Connection tubing Software option for diffusion loss correction Uses hardware settings to estimate diffusion loss and apply correction Empirical and calculated contributions. Can apply diffusion loss correction to previously collected data

Diffusion Loss Algorithm Example Ambient Air Without correction With correction

Aggregates Z p derivation assumes spherical model for drag force Equilibrium charge distribution based on spheres Nanoparticle aggregate correction option Input estimated primary particle size estimated agglomerate orientation (typically parallel) Can apply to previously collected data Lall & Friedlander (2006)

Aggregate Correction - Example Spherical assumption: red Aggregate correction: green Primary particle diameter = 17nm Parallel orientation 500x10 3 Number da/dlog(d 2 /cm 3 m ), nm 18x10 9 16x10 9 14x10 9 12x10 9 10x10 9 8x10 9 6x10 9 4x10 9 Surface Area dv/dlog(d m ), #/cc 250x10 9 200x10 9 150x10 9 100x10 9 50x10 9 0 Mass 10 100 1000 Mobility Diameter (d m ), nm dn/dlogd m, #/cc 400x10 3 300x10 3 200x10 3 2x10 9 0 10 100 1000 Mobility Diameter (d m ), nm Aggregate drag model (Chan & Dahneke 1981) 100x10 3 Aggregate charge distribution (Wen et al 1984) 0 10 100 1000 Mobility Diameter (d m ), nm

ISO 15900:2009 ISO 15900:2009 Determination of particle size distribution Differential electrical mobility analysis for aerosol particles Détermination de la distribution granulométrique Analyse de mobilité électrique différentielle pour les particules d'aérosol Aimed at user; not developers Describes differential electrical mobility analysis Raises awareness Gives guidance on important issues Slip correction factor Size dependent charge distribution Methods for data inversion Table 1 Values of Parameters Recommended for the Calculation of the Electrical Mobility From the Particle Size in Air ISO 10808:2010 ISO 28439:2011 Characterization of nanoparticles in inhalation exposure chambers for inhalation toxicity testing Workplace atmospheres -- Characterization of ultrafine aerosols/nanoaerosols -- Determination of the size distribution and number concentration using differential electrical mobility analysing systems

Nanoparticle Colloids (Sols) ES + SMPS Sizing Nanoparticles In Liquids Electrospray + SMPS = ES+SMPS Increased interest in the last decade for high resolution liquid nanoparticle sizing Wide array of peer reviewed publications Gold (Au) [Bottinger et al 2007, Tsai et al 2008] Carbon Nanotubes (CNT), [Pease et al 2009] Protein-coated Quantum Dots (QD), [Pease et al 2010] Copper (Cu), [Elzey et al 2010] Silver (Ag), [Elzey et al 2010] Iron Oxide (Fe x O y ),[Hildebrandt et al 2010]

Closing Comments Scanning Mobility Particle Sizing Rapid, high resolution size nanoparticle size distribution measurements Discreet technique with large sample size No assumptions regarding size distribution Low uncertainty Easy to use Useful for: 1. liquid aerosols 2. solid aerosols 3. nanoparticles suspended in liquids (sols) Considerations Measures mobility particle size is calculated Limits to particle size range; <1µm Proper neutralization is fundamental Size resolution can be degraded by 1. Design defects: imperfect flow fields or electric fields 2. Low voltages: increases diffusion broadening decreases resolution 3. Too short of scans dn/dlogdp (#/cm3) [e7] Ovalbumin (AG501-X8) 3.22 3.72 4.61 6.38 8.20 Mobility Diameter (nm)

Thank You For Your Attention Any Questions? Kathy Erickson (kerickson@tsi.com)

TSI PARTICLE NEWS Webinar Schedule May 5 th Using TDMAs to Measure Haze by Tim Johnson www.tsi.com/webinars May 19 th June 23 rd July 21 st Electrospray with SMPS (ES+SMPS) for Size Measurements of Nanoparticles Suspended in Liquids by Dr. Stan Kaufman Indoor Exposure to Ultrafine Particles: Sources and Measurements by Dr. Lance Wallace Toxicological Evidence that Inhalation of Nanoscale Particulates in Urban Air Pollution is Associated with Cognitive Impairment by Dr. David Davis (USC) Optical Particle Sizer Model 3330 Size resolution <5% at 0.5µm User adjustable size channels Size range: 0.3 10µm in up to 16 channels Wide concentration range from 0 to 3000 particles/cm 3 Fully compliant with ISO 21501-01/04 New WCPC s Models 3787 & 3788 Model 3788 2.5nm detection Single particle counting to 4x10 5 particles/cm3 <100 ms rise-time response w/ 42 ms time constant (fastest CPC available) Convenient, eco-friendly water as working fluid www.tsi.com US +1 651-490-2811 EURO +49 241-52303-0 ASIA + 86 10 8251 6588 info@tsi.com