Techniques for Determining PSD of PM: Laser
Diffraction vs. Electrical Sensing Zone
A 242nd ACS National Meeting Presentation: Paper ID18440
Z. Cao1, M. Buser2, D. Whitelock3, L. Wang-Li*1, Y. Zhang4, C.B.
Parnell5
1NCSU, 2OSU, 3USDA-ARS, 4UIUC, 5TAMU
Introduction:
• PM – NAAQS: PM10 & PM2.5
• Health effects, Source identification/estimation,
Mitigation strategies – PM characteristics:
Physical properties
 Mass, or number concentrations
 Particle size distribution (PSD)
 Morphology
 Density, etc.
 Chemical compositions
 Biological properties
Introduction:
• Various techniques for PSD measurement (analysis)
 Aerodynamic method (APS, Impactors, etc)
 Optical method (optical counters, light scattering
analyzers, etc)
 Electrical sensing zone method (Coulter Counter)
 Electrical mobility and condensation method
(DMA+CNC)
 Electron microscopy
• No single agreed upon method – for different sources
Aerodynamic Method for PSD Analysis:
Aerodynamic Particle Sizer (APS)
• Aerosol entering the tube is assumed to be uniform
• Dilution system - reduce problems with particle
coincidence in the sensor
• Light scattered - changes rapidly with dp:

small particle processor : AED 0.5 – 15.9 mm

large particle processor: AED 5 – 30 mm
• Monodisperse latex spheres are used for calibration
of full size range of the APS
• Not work for PSD on sampler filter
• Field real-time measurement
Ch5.8: pages 136-138 of Hinds
Aerodynamic Method for PSD Analysis:
Impactors
• On-site measurements in mass
concentration and PSD
• Limited size ranges
• Particle bounce
• Particle losses
Optical Method for PSD Analysis:
Optical Particle Counters
http://en.wikipedia.org/wiki/Particle_counter
• Detect and counts one particle at a time
• Calibration?
http://www.particlecounters.org/optical/
• High level PM environment?
Optical Method for PSD Analysis:
LS13 320 Multi-wave Length Laser Diffraction
Particle Size Analyzer (0.04 – 2000 mm)
Polarization Intensity Differential Scattering (PIDS)
Rayleigh Scattering Theory
Mie Scattering theory
(Source: Beckman Coulter, Miami, FL)
Optical Method for PSD Analysis:
LA-300 Laser Scattering Particle Size Analyzer
Fraunhofer Diffraction and LA-300 (Source: Horiba Instrument Inc, Irvine, CA)
Electrical Sensing Zone Method for PSD Analysis:
Coulter Counter Multisizer
• Only suitable for insoluble
particles
• Not an onsite measurement
• Ultrasonic bath – all particles are
fully dispersed in the liquid
solution (PM on filter)
Source: Beckman Coulter, Miami, FL
• Current through the orifice
• Particle electrical resistance ~ dp
• Change in current ~ dp
• Size calibrated with polystyrene
spheres of known size
• Counting rate – 3000 particles/s
Electrical Mobility Method for PSD Analysis:
Differential Mobility Analyzer
(DMA)
• Used as a monodisper aerosol generator to
produce sub-micrometer-sized aerosols for
testing and calibration
• Measure PSD in the sub-micrometer size
range
Condensation Nucleus Counter (CNC)
• Particles with greater mobility migrate to the
center rod
• Exiting aerosol – slightly charged and nearly
monodisperse –size controlled by the voltage
on the central rod
• 0.005 – 1.0 mm
Ch15.9 of Hinds
Electron Microscopy Method for PSD Analysis:
Electron Scanning Microscopy (ESM)
Fly-ash
Corn Starch
Objectives:
• Differences in PSD measurements for PM with
MMDs in micrometers (agricultural sources)
 Light scattering method
 Electrical sensing zone method
• PM sample types
• Filter-based PM samples with MMD>>10 mm
• Testing aerosols with MMD ~ 10 mm
Materials & Methods
PSD Analyzers
 LS13 320 multi-wave length laser diffraction
particle size analyzer - NCSU
 LA-300 laser scattering particle size analyzer –
UIUC
 Coulter Counter Multisizer3 – TAMU
 Coulter Counter Multisizer3 – USDA
LS230 laser diffraction particle size analyzer –
USDA
Materials & Methods
PM Field Sampling – Low-volume TSP Samplers
High-rise Layer House
(a)
(b)
(c)
(d)
Materials & Methods
• Field PM samples: filter-based
26 samples/season for two seasons: distributed to the
three locations
Analyzed under the same operation procedure
• Testing materials: not filter-based aerosols
Limestone
Starch
No.3 Micro Aluminum
No.5 Micro Aluminum
Materials & Methods
PM Sample Assignment/Distribution
PM Samples
NCSU
LS13 320
UIUC
LA-300
TAMU
CCM3
USDA
CCM3
Winter PM samples
Spring PM samples
Testing aerosols
Winter PM samples
LS230
Spring PM samples
Testing aerosols
Materials & Methods
• PM10 and PM2.5 mass fraction analyses
Measured by the analyzer
Calculated using the lognormal distribution equation
Checked for agreements (Relative Difference, %)
Measured  Lognormal
RD 
 100%
Measured
Measured = PM10 or PM2.5 measured by the analyzer
Lognormal = PM10 or PM2.5 calculated using the lognormal
distribution equation
Results & Discussion
Measured MMDs (mm) for Winter Samples: N=26
LS13 320
17.13±0.81
LA-300
22.71±1.43
CCM3
13.94±1.00
Results & Discussion
Measured GSDs for Winter Samples: N=26
LS13 320
2.63±0.04
LA-300
2.02±0.11
CCM3
1.85±0.04
Results & Discussion
Measured MMDs (mm) for Spring Samples: N=26
LS13 320
18.44±1.44
LA-300
22.62±2.68
LS230
18.47±1.38
CCM3
13.99±0.74
Results & Discussion
Measured GSDs for Spring Samples: N=26
LS13 320
2.67±0.11
LA-300
1.99±0.15
LS230
2.65±0.22
CCM3
1.84±0.04
Results & Discussion
Measured PSDs of Testing Aerosols
LS13 320
LA-300
LS230
CCM3
Testing aerosols
MMD
(µm)
GSD
MMD
(µm)
MMD
(µm)
GSD
MMD
(µm)
GSD
Limestone
7.50
3.07
12.29 1.83
8.11
3.15
8.56
1.72
Starch
13.31 1.59
16.78 1.50
14.38 1.55
14.32 1.33
#3 Micro aluminum
5.28
1.98
7.62
1.56
5.37
1.93
5.03
1.42
#5 Micro aluminum
7.09
1.69
8.38
1.49
7.21
1.71
6.31
1.39
GSD
Results & Discussion
Results & Discussion
Results & Discussion
PM10 and PM2.5 Mass Fraction Analyses (NCSU)
LS13 320
Measured mass
fraction (%)
Lognormal mass
fraction (%)
Relative
difference (%)
PM10
36.16±2.73
34.92±2.71
3.44±0.85
PM2.5
8.40±0.61
3.56±0.66
57.9±5.37
N=52 (26 for Winter, 26 for Spring)
Results & Discussion
LS13 320
PM10
PM2.5
N=52
26 for Winter
26 for Spring)
Results & Discussion
PM10 and PM2.5 Mass Fraction Analyses (UIUC)
LA-300
Measured mass
fraction (%)
Lognormal mass
fraction (%)
Relative
difference (%)
PM10
20.60±2.53
19.88±2.56
3.34±5.34
PM2.5
4.57±0.64
0.25±0.14
94.46±3.05
N=52 (26 for Winter, 26 for Spring)
Results & Discussion
LA-300
PM10
PM2.5
N=52
26 for Winter
26 for Spring
Results & Discussion
PM10 Mass Fraction Analyses (TAMU)
CCM3
PM10
Measured mass
fraction (%)
Lognormal mass
fraction (%)
Relative
difference (%)
41.75±3.74
40.76±4.19
2.46±2.06
N= 26 for Winter
Results & Discussion
TAMU-CCM3
(N=26)
Results & Discussion
PM10 and PM2.5 Mass Fraction Analyses (USDA)
PM10
Measured mass
fraction (%)
Lognormal mass
fraction (%)
Relative
difference (%)
33.71±3.29
33.39±2.99
0.79±4.45
LS230
PM2.5
8.18±0.96
3.28±1.06
60.44±11.53
PM10
41.11±3.68
40.93±3.50
0.39±0.80
0.65±0.26
54.96±13.04
CCM3
PM2.5
1.43±0.35
N= 26 for Spring
Results & Discussion
LS230
PM10
PM2.5
N=26 for Spring
Results & Discussion
CCM3
PM10
PM2.5
N=26 for Spring
Conclusions
• Different analyzers: significant differences in MMDs and
GSDs for filter-based samples
 LA-300: the largest MMDs; CCM3: the smallest MMD
 LS13 320: the largest GSDs; CCM3: the smallest
• The PSD results of testing aerosols - consistent with that of
filter-based samples
 LA-300: large MMDs
 LS13 320 & LS230: large GSD
• PSDs measured by LS13 320 & LS230 agreed well
Conclusions
• All RDs in PM10 mass fractions of the measured and
the fitting values < 5%, which is acceptable
• All RDs in PM2.5 mass fractions of the measured and
the fitting values >> 5%, which is not acceptable.
Acknowledgement
• The USDA NRI Grant No. 2008-35112-18757
• Help from Qianfeng Li & Zifei Liu for field
sampling
• Support from the egg production farm