Calibration checks of particle counter using primary and other techniques at the laboratory level

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1 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 , Particulate Workshop (GAWG), BIPM April 15, 2015 (aggarwalsg@nplindia.org)

2 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.

3 Particle counter and principles. Each counting principle has a range of particle size measurements with uncertainties.

4 Patent and publication search

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7 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.

8 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.

9 Our approach We used scanning mobility particle sizer (SMPS) consists of a DMA (TSI 3081) and CPC (TSI 3788)

10 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

11 CPC Schematic of condensation particle counter (CPC)

12 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 nm were segregated by DMA and number concentration was measured by CPC.

13 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 cm 3, v is the flow volume (calculated from CPC inlet flow and the time of flow) enters to CPC, d pi and n i are the particle size and number concentration in bin i

14 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, g/cm 3 ), m is the mass of the particles collected on the filter.

15 Table 1: Particle volume calculated from both filter and CPC Our approach (CPC derived volume vs. filter based volume) Ammonium sulfate particles (14-615nm)

16 Results suggest that this approach can be used for calibration of PM samplers as well.

17 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.

18 Team members: Prabhat K. Gupta, Bighnaraj Sarangi, Sudhanshu Kumar, Khem Singh, Anil Kumar March 20, :33 AM Temperature 18º C Humidity 89% March 21, :32AM Temperature 18º C Humidity 83%