Calibration checks of particle counter using primary
and other techniques at the laboratory level
Shankar G. Aggarwal, Ph.D.
CSIR-National Physical Laboratory, New Delhi-110 012, India
@ Particulate Workshop (GAWG), BIPM
April 15, 2015
([email protected])
Particle counter and principles ….
1. Optical Particle Counter (OPC)
It counts particle by the measurement of scattered light of individual
particles. The OPC technique is only applicable for particle above 100
nm.
2. Condensation Particle Counter (CPC)
Particles undergo condensational growth on
a working liquid and are detected/counted by
light scattering technique (3 nm above).
3. Faraday Cup Electrometer (FCE)
Particles are charged singly first, and then they
are counted by number charges. However, it is
assumed that all particles get single charge. In
this manner charging of bigger sized particles is difficult.
Particle counter and principles ….
Each counting principle has a range of particle size measurements with
uncertainties.
Patent and publication search…
Limitation….
•
Mostly electrometer based, which needs particles to be
charged singly, in practice it is highly difficult ,especially
for >100 nm particles.
•
Over estimation due to multiple charge on the particle.
•
Alternatively reference counter is used, which has to be
calibrated (against electrometer).
•
Inconvenient for inter-comparison studies. Need to ship
all counters from participant laboratory at one laboratory
for one-source particle feeding to each counter.
We need….
•
A method through which we can calibrate (calibrate
checks) the counters those work at different particle
concentration range.
•
Should be useful to use for PM2.5 and PM10 sampler
calibration.
•
Should be useful for inter-comparison study in which
device should not be needed to transfer to a particular
laboratory.
Our approach…
We used scanning
mobility particle
sizer (SMPS)
consists of a DMA
(TSI 3081) and
CPC (TSI 3788)
SMPS includes DMA & CPC
Scanning mobility particle sizer (SMPS) consists of a DMA (TSI
3081) and CPC (TSI 3788).
Schematic of Electrostatic Classifier including Nano and long DMA
CPC
Schematic of condensation particle counter (CPC)
Our approach… (CPC derived volume vs. filter based volume)
This approach is based on the comparison of particle volumes derived from scanning
mobility particle sizer (SMPS) with corresponding particle volume, which are collected on
filter and determined by mass (gravimetric method).
Dried ammonium sulfate particles were introduced to SMPS and particles of size range 14
- 615 nm were segregated by DMA and number concentration was measured by CPC.
Our approach… (CPC derived volume vs. filter based volume)
Using CPC particle count data, CPC derived particle
volume can be calculated as:
where , V is the total volume of the size distribution in cm3,
v is the flow volume (calculated from CPC inlet flow and the
time of flow) enters to CPC, dpi and ni are the particle size
and number concentration in bin i
Our approach… (CPC derived volume vs. filter based volume)
Based on the particle mass collected on the filter, and
using density of particle material (e.g., ammonium sulfate),
we have calculated the volume of particles as:
where, ρ is the density of particle material (e.g., in case of
ammonium sulfate, 1.769 g/cm3), m is the mass of the
particles collected on the filter.
Table 1: Particle volume calculated from both filter and CPC
Our
approach… (CPC derived volume vs. filter based volume)
Ammonium sulfate particles (14 - 615nm)
Results suggest that this approach can be used for calibration of
PM samplers as well….
Summary…
•
A particle gravimetric mass-volume based method is invented for counting
efficiency/calibration check of a particle counter.
•
Salt , PSL particles can be re-aerosolized using atomizer/nebulizer for
generation of wide particle size range. These salts are easy to ship, stable
for a longer duration of time, cost effective and easily available.
•
1 µg/ 0.1 µg precision mass balance can be used for filter weighing.
•
OPC, CPC can be deployed as test device.
•
Process is based on primary method traceable to SI unit.
•
simple and relatively cost effective method (based on instruments which
are readily available in a particle research laboratory), so can be applied at
on laboratory scale facilities.
•
This method can be useful for inter-comparison studies in which particle
counters from different laboratory should not be needed to ship in a
particular laboratory.
Team members:
Prabhat K. Gupta, Bighnaraj Sarangi, Sudhanshu Kumar,
Khem Singh, Anil Kumar
March 20, 2013 06:33 AM
Temperature 18º C
Humidity 89%
March 21, 2013 06:32AM
Temperature 18º C
Humidity 83%