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Penetration Calibration and Verification for the Solid Particle Counting System with Polydisperse and Monodisperse Particles
Abstract:
Monodisperse and polydisperse Sodium Chloride (NaCl) particles were used to calibrate the solid particle penetration for the Volatile Particle Remover (VPR) in a Horiba prototype Solid Particle Counting System (SPCS). Prior to the calibration, dilution ratios on the SPCS are verified carefully with a flame ionization analyzer (FIA). Size distributions for polydisperse aerosols upstream and downstream of the Volatile Particle Remover (VPR) were measured with a Scanning Mobility Particle Sizer (SMPS). It is found that overall penetrations for polydisperse aerosols are larger than 95%. Geometric standard deviations from the raw and the diluted by the VPR are within ±1.5% difference. Thus, shapes of size distributions aren't changed after dilution. Geometric mean diameters shift a little, on average ±5% after dilution. Therefore, the VPR doesn't change the aerosol characteristics after the aerosol is diluted and heated up to 320 °C.
Penetrations with monodisperse solid particles meet current PMP recommendation. Minimum solid particle penetrations for 30 nm, 50 nm, and 100 nm particles are found at 78.2%, 90.6%, and 81.4% respectively. At 30 nm, penetrations show a big variation with dilution ratios. One of reasons may be due to higher sample flow to reduce the diffusion losses in the system; and the other reason may be due to uncertainties induced by the low detection efficiency at 30 nm for the condensation particle counter (CPC) and low upstream aerosol concentration.
It may be a good practice to evaluate the penetration of the VPR by measuring upstream and downstream polydisperse aerosol size distributions although it isn't recommended by PMP at this moment. It gives more information about the VPR performance than the monodisperse particle described by the PMP. In the meantime, the polydisperse aerosol is easier to be generated and handled.