Particle Size and Size Distributions Methods for Measuring Particle Size and Size Distributions Peter H. McMurry Department of Mechanical Engineering University of Minnesota

Measures of Particle Size Light Scattering: f (n, “size”, shape) Electrical Mobility: g ( “size”, shape) Aerodynamic size: h (r, “size”, shape) Mass: I (r, “size”) where n = complex refractive index r = particle density “size”= a measure of geometric size (e.g., diameter of sphere)

Measurement of Particle Size Light Scattering: Optical Particle Counter (OPC) Electrical Mobility: Mobility Classifier + Condensation Particle Counter (SMPS) Aerodynamic size: Aerodynamic Particle Sizer Mass: Aerosol Particle Mass Analyzer + Concensation Particle Counter

An Instrument System for Measuring Size Distributions (3 nm - 10 µm) (Used by UMN at St. Louis Supersite)

OPC1 (Auto Calibrated hourly @ 450 nm) 0.1 µm < Dp < 2 µm PM10 Inlet RH Control 38%<RH<42% Nano-SMPS 3 < Dp < 40 nm SMPS 20 < Dp < 300 nm OPC1 (Auto Calibrated hourly @ 450 nm) 0.1 µm < Dp < 2 µm OPC2 (Auto Calibrated hourly @ 450 nm) 0.1 µm < Dp < 2 µm

Size Distribution Measured in Atlanta During Nucleation Event (April 1, 1999 12:00; Woo, McMurry et al.) 0.1 1 10 100 1000 10000 100000 1000000 10000000 Nucleation Mode 0.1 1 10 100 1000 Accumulation Mode Aitken Nuclei Mode Scale for number distribution is shown at LHS and for volume distribution is shown at RHS. Note that these are logarithmic scales. These data were measured during a nucleation event. (Note the sharp rise in number concentrations for particles smaller than about 7 nm). The data acquisition system was designed to provide overlap for measurements from our three instruments. We used this overlap to help in evaluating data quality. If data from different instruments in the overlap region were systematically different, then we examined the data in more detail to determine whether discrepancies were due to improper operation of one of the instruments. dN/dLogDp dV/dLogDp 0.001 0.01 0.1 1 10 Dp, µm

Ultrafine Particle Events Observed in St Ultrafine Particle Events Observed in St. Louis (Shi, Sakurai and McMurry) Regional Nucleation Event “SO2 Plume” Event NOx-CO Event (Traffic)

We can do good job (90% data recovery) of measuring size distributions routinely, remotely and continuously (5 minute resolution) However “Size” is not always a well defined parameter, and external mixing further complicates our ability to relate one measure of size to another

3 2 1 4 Response of various instruments to DMA-classified particles r Outer electrode Mass classified aerosol Z Aerosol entrance w Inner electrode r2 r1 High voltage Dry air Aerosol Inlet Neutralizer APM w 3 2 1 DMA MOUDI OPC (Lasair) CNC 3760 Vacuum pump Orifice TEM 4

More typical higher mass particles (probably “Fluffy” Sulfate/OC DMA + APM Measurements; 1999 Atlanta SuperSite Experiment: Distributions of mass for particles with mobility size =0.309 µm More typical higher mass particles (probably Sulfate/OC spheres) “Fluffy” low mass Particles (probably Soot)

DMA + OPC: Light Scattering response to 450nm diesel soot and atmospheric particles dark particles bright particles

For Diesel Exhaust Particles Relationship between mobility, optical equivalent and aerodynamic diameters For Diesel Exhaust Particles Relationship between aerodynamic and mobility diameters Relationship between optical equivalent and mobility diameters A PMS Model 1002 Lasair OPC calibrated with DOS spheres measured the optical equivalent size of DMA-classified diesel exhaust particles

DMA + TEM (70 nm mobility size particles (John Deere Engine, 1400 rpm, 10% load, Two distinct peaks are observed when heated)

TDMA Particle Growth Measurements 5 - 85% RH 5% RH Dp(5%) = .05, .1, .2, .3, .4 mm Dp (RH) Ratio of total water volume to dry particle volume: (Volume addivity assumed)

Separation of “More” and “Less” Hygroscopic Particles by TDMA

Morphology and Composition of a “Less Hygroscopic” Particle (McMurry et al., 1996)

Morphology and Composition of a “More Hygroscopic” Particle (McMurry et al., 1996)

DAWN-A MALS Instrument

Laboratory Measurements (DMA + MALS)

0.5 µm Nonspherical Fractions Dry: RH = 4-10% Wet: RH = 44-76%

Atmospheric Measurements (DMA + MALS) Wet 0.5 µm Dry 0.5 µm

Model vs. Measured Refractive Index 0.3 µm (DMA + MALS)

Lecture Outline Physical Characteristics Chemical Characteristics Improved measurements of size distributions Particle nucleation and growth Particle Properties: Mixing characteristics Hygroscopicity, Density, Refractive Index Chemical Characteristics Real-time measurements Single particle mass spectrometry

Physical Characteristics

Instrumentation: 3 nm to 10 µm Size Distributions -RH control -Autocalibrate -Remote control

Nucleation and Growth

Comparison of Nanoparticle Growth Rates in St Comparison of Nanoparticle Growth Rates in St. Louis and Atlanta (Shi, Woo, Sakurai, McMurry; 2003)

Mixing Characteristics and Hygroscopic Properties

Physical Properties Density and Refractive Index

TDMA-APM system (Park, McMurry et al.) Compressed air MFC Dry air Wet air Saturator Vacuum pump Orifice Neutralizer Dryer Sheath air DMA1 HEPA ω APM CNC 3760

Multiangle Light Scattering (MALS) (Dick & McMurry, 1998)

Application of MALS to Atmospheric Particles (Dick & McMurry, 1998) Wet 0.5 µm Dry 0.5 µm

Model vs. Measured Refractive Index: Application of MALS to 0 Model vs. Measured Refractive Index: Application of MALS to 0.3 µm Particles (Dick & McMurry, 1998)

Chemical Characteristics: New Insights from Real-Time Measurements

Satellite Sites Outside Pittsburgh (Stainer, Pandis et al.) Florence Steubenville Wheeling Greensburg Holbrook Athens

Regional Nucleation event in Pittsburgh Area (February 25, 2002; Stainer, Pandis et al.)

Diameter Growth Rate During Regional Nucleation Events in St Diameter Growth Rate During Regional Nucleation Events in St. Louis (Shi, Sakurai and McMurry, 2003) Particles tend to grow faster in summer

Annual Average Diurnal Patterns in St Annual Average Diurnal Patterns in St. Louis and Atlanta: 3 to 10 nm Number Concentrations

Annual Variations in Number Concentrations for St Annual Variations in Number Concentrations for St. Louis and Atlanta: 10 to 100 nm

Particle Mass Measurement with the Aerosol Particle Mass Analyzer (APM; Ehara et al., 1996) High Voltage r qE mw2r

(Atlanta ambient aerosols; McMurry et al., 2002) Particles of a Given Mobility Size can have Several Distinct Masses (Effective Densities) (Atlanta ambient aerosols; McMurry et al., 2002)

Effective Densities of Diesel Exhaust Particles (Park, McMurry et al., 2002)

“Excess” Water vs. Organic Mass (Dick & McMurry, 1998)

Numerical Simulation of the Formation of Particle Beams with Aerodynamic Lenses (Peng Liu et al, 1994) -Width of particle beam is determined by Brownian Motion of particles in the nozzle and by lift forces which act on irregularly shaped particles and increases with decreasing particle size.

Annual Variations in Number Concentrations for St Annual Variations in Number Concentrations for St. Louis and Atlanta: 3 to 10 nm

Annual Average Diurnal Patterns in St Annual Average Diurnal Patterns in St. Louis and Atlanta: 10 to 100 nm Number Concentrations

Annual Average Diurnal Patterns in St. Louis and Atlanta: 0 Annual Average Diurnal Patterns in St. Louis and Atlanta: 0.1 to 2 µm Number Concentrations