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

2. 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)

3. 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

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

5. 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 450 nm)
0.1 µm < Dp < 2 µm
OPC2 (Auto Calibrated 450 nm)
0.1 µm < Dp < 2 µm

6. Size Distribution Measured in Atlanta During Nucleation Event (April 1, :00; Woo, McMurry et al.)
0.1 1 10
100
1000
10000
100000
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

7. 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)

8. 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

9. 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

10. 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)

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

12. 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

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

14. 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)

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

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

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

18. DAWN-A MALS Instrument

19. Laboratory Measurements (DMA + MALS)

20. 0.5 µm Nonspherical Fractions
Dry: RH = 4-10%
Wet: RH = 44-76%

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

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

24. 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

25. Physical Characteristics

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

27. Nucleation and Growth

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

29. Mixing Characteristics and Hygroscopic Properties

30. Physical Properties Density and Refractive Index

31. 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

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

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

34. 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)

35. Chemical Characteristics:
New Insights from Real-Time Measurements

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

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

38. 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

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

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

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

42. (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)

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

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

45. 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.

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

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

48. 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