JASIC Comments of calibration procedure on Particle measurement system
March 30, 2010
Objective
The particle number measurement procedure was issued as supplement for ECE Reg.No.83 last
year. The problems for the new measurement and especially for the calibration are recognized and
remarked in the minutes of PMP informal meeting held in October 2007.
The measurement
instrument industries are collecting data to improve the method, however, we believe that the
consideration from the experts of automobile cannot be ignored.
We have studied the new measurement procedure, particularly the calibration of the particle
measurement system, and as a result, several points to be improved are found. Here is our study
result on the calibration procedure and our proposals to improve the procedure are also presented.
We expect that these comments will be examined among the experts and contribute to accurize the
PN measurement procedure to be introduced in 2011.
Proposal for the improvement of calibration procedure
(1) Monodispersity measurement of calibration particles
---We propose either of these two ideas below.
Idea 1. Evaluate the monodispersity with full width of half Maximum of peak (not GSD )
Idea 2. Define clear description of particle measurement procedure when evaluating the
monodispersity with GSD.
--- Define the concentration of PNC before GSD measurement. (example: <0.01unit/cm3)
--- Measurement range of SMPS should be as narrow as possible.
(example: Seath air flow should be set at 15L/min when measuring 100nm particle.)
--- Scan speed should be low as soon as possible. (example: 120 s at measuring 100nm)
(2) Definition of calibration particles
---Material, generation, and diameter should be defined for the particles for measurement.
Linearity check
The material shall be defined. (example: Carbon particles)
Note: Particles for calibration shall be neutralized adequately in order to prevent the counting
error caused by multiply charged particles.
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Procedure of generation shall be defined. (example: Electric discharge or combustion)
Particle diameter shall be defined. (delete the range) (example: 90nm)
monodispersity: GSD<1.2
or Full width of half Maximum of peak is +-10%
Cut off check
The material shall be defined. (example: Carbon particles)
Note: Particles for calibration shall be neutralized adequately in order to prevent the counting
error caused by multiply charged particles.
Procedure of generation shall be defined. (example: Electric discharge or combustion)
Particle diameter: 23nm, 41nm
monodispersity: GSD<1.2
or Full width of half Maximum of peak is +-10%
(3) Definition of VPR calibration particles
As for the particles for pcrf check, its material and generation should be defined.
The material shall be defined. (example: Carbon particles)
Note: Particles for calibration shall be neutralized adequately in order to prevent the counting
error caused by multiply charged particles.
Procedure of generation shall be defined. (example: Electric discharge or combustion)
monodispersity: GSD<1.2
or Width of half value of peak is +-10%
(4)Demand of PNC for PNC cut off check and VPR pcrf check
PNC should have counting efficiency above 90% at 23nm particles.
(5)Calibration particles for PNC and VPR should be the same material.
(6) Allowance of VPR pcrf at 30nm should be reviewed as soon as possible. (i.e. 30%- 20% or less)
Large allowance for VPR may cause overestimation or underestimation depending on the
dispersity of particle diameter, and it is recognized as “future work” at the informal meeting in
October 2007. We expect to solve this issue at early stage.
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Study result on accuracy of the measurement instrument
(1) General description of calibration system
The test particles were generated by particle generator or engine exhaust. Those particles were
transmitted to the particle number counter (PNC) and the electrometer through the differential
mobility analyzer. The value of particle number counter was compared to that of the electrometer.
(Fig. 1)
HEPA
Electrometer (reference)
flow splitter
Aerosol generator
Diluter
Neutralizer
Electrostatic
classifier
PNC （under validation)
Fig. 1 Outline of calibration system
(2) Issues of measuring the monodispersity (GSD)
The monodispersity of particles used by calibration is specified as less than 1.2 in the GSD. This
GSD value varies to a large amount according to the initial state, measurement diameter range and
measurement period and it might affect the calibration results.
Fig. 2 shows the result of initial concentration of CPC.
Fig. 3 shows the result of preset Scanning Mobility particle sizer coverage.
1.E+06
Sheath：15L/min Scan up：120s
case A: GSD1.19
1.E+05
case B：GSD1.41
1.E+04
1.E+03
1.E+02
1.E+01
case B：cause of GSD increase
1.E+00
Particle concentration (#/cm3)
Particle concentration (#/cm3)
Fig. 4 shows the result of preset scanning speed of SMPS.
Scan up 90s , Particle diameter = 100nm
1.0E+06
15L/min GSD
6L/min 15L/min：1.19
6L/min：1.23
1.0E+05
1.0E+04
1.0E+03
1.0E+02
1.0E+01
1.0E+00
0
100
200
300
400
500
Particle diameter Dp (nm)
1
10
100
1000
Particle Diametr Dp (nm)
Fig.3 Influence of preset Scanning Mobility
Fig.2 Influence of initial concentration
particle sizer coverage
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1.6E+05
GSD
1.2E+05
1.2
8.0E+04
4.0E+04
GSD
peak conc.
1.1
0.0E+00
50 60 70 80 90 100 110 120 130
peak concentration (#/cm3)
1.3
SMPS_Scan up speed （s)
Fig.4 Influence of preset scanning speed of SMPS
The influence of the difference of GSD value, i.e., the sharpness of calibration particle was not
prominent as far as the data in this document shows. However, it is still foreseen that there might
occur more difference under the same GSD value if the particle size distribution differs, so more
precise measurement procedure is desired.
This study was conducted with the particle diameter (23nm) close to the PNC cut off check which is
likely to easily reflect the difference. The GSD value varied from 1.08 to 1.16, and there was not
100
80
Counting efficiency(%)
Counting efficiency(%)
much change in the counting efficiency. (Fig.5, Fig 6)
50
70
60
50
40
30
20
0
1
23
41
Particle diameter (nm)
1.05
1.1
GSD
1.15
1.2
Fig.6 Influence of the GSD value close to the
Fig.5 PNC cut off check
PNC cut off check（23nm particle）
(3) Issues of PNC linearity check on calibration/validation
Since material and diameter of the particle for calibration is not specified, number counting value
will be different according to its material and diameter. Counting value of PNC may not show exact
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value when the difference from the actual particles emitted from vehicles is large.
-Depending on the sort of particle, the correlation with the electrometer varies.
The
measurement principles of the electrometer and PNC are different, so as the influencing factor
for the PN measurement, the values from these two instruments cannot be always equal.
However, it is important that the particle should have similar characteristics to that of particle
emitted from vehicle as the measurement object is particle emitted from the vehicle. (Fig. 7, Fig.
8)
-Particle diameter size for calibration is specified as between 50nm to 100nm. The gradient of the
correlation (K factor) depends on the particle diameter. (Fig. 7)
The gradient of 50nm particle is smaller than that of particle of 90nm by 5% or more, so it is
important to specify the diameter size. Furthermore, it is desirable to set the larger value for
diameter because the smaller size of particle diameter causes larger dispersity.
12000
12000
Emery Oil
Diesel exhaust
Carbon
Gasoline exhaust
10000
3010D (#/cm3)
8000
50nm
6000
4000
8000
6000
4000
2000
2000
0
0
0
0
2000 4000 6000 8000 10000 12000
2000 4000 6000 8000 10000 12000
Electrometer (#/cm3)
Electrometer (#/cm3)
Fig.7 Influence of the sort of particle (50nm)
gradient of the correlation
3010D (#/cm3)
10000
Emery Oil
Diesel exhaust
Carbon
Gasoline exhaust
80nm
Fig.8 Influence of the sort of particle (80nm)
1
0.9
0.8
0.7
0.6
40
50
60
70
80
90
100
Particle diameter(nm)
Fig.9 Influence of the particle diameter (Emery oil)
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(4) Issues of PNC cut off characteristic check on calibration/validation
<General>
-In the document issued by AEA, the reference instrument (i.e. electrometer) is not described for the
cut off characteristic calibration. Procedure of cut off calibration should be described as well as
the linearity check.
-Characteristic of reference PNC using cut off calibration should be defined. The instruments which
meet the objective to measure small particles should be used, otherwise the measurement
conditions such as ambient temperature would affect the measurement result.
<Issues on calibration/Validation>
-Counting efficiency of 23nm particles depends on particle materials. (Fig. 10)
- Considering the major point of the regulation to measure the particles more than 23nm, the
counting efficiency check by emery oil which is conducted by measurement instrument
manufacturers might cause the cut off characteristics that widely differs from those of particles
emitted by vehicle.
-Although monodispersity of calibration particles is defined as less than 1.1, it does not influence
100
Emery Oil
Carbon
NaCl
80
60
particle emitted from SI
40
20
0
0
5000
Counting efficiency(%)
Counting efficiency(%)
the cut off characteristic. GSD<1.1 regulation may be loosed to GSD<1.2. (Fig. 11)
10000
80
70
60
50
40
30
20
1
1.05
1.1
GSD
1.15
1.2
Particle concentration(#/cm3)
Fig. 11 Influence to GSD
Fig. 10 Influence of the sort of particles
to the counting efficiency
to the counting efficiency
(5) Issues of VPR characteristic check on calibration/validation
-VPR calibration particles are not specified and same problem as in PNC could occur. Same
particles should be specified to the PNC calibration.
-The PNC specification is not mentioned for the measurement of VPR pcrf. Under the instrument
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proposed by PMP, the measurement at 30nm particle is done near the PNC cut off point, which
has very low efficiency. Very low efficiency brings low accuracy.
Conclusion
We expect that these comments will be examined among the experts at the informal meeting in
March, and continue the discussion based on technical data to develop more elaborated PN
measurement procedure.
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