A method of testing size resolution of a particle sizing instrument Toward traceable particle measurements

Transcription

1 A method of testing size resolution of a article sizing instrument Toward traceable article measurements K. Ehara, Y. Sato, H. Sakurai, and K. Takahata National Metrology Institute of Jaan National Institute of Advanced Industrial Science and Technology, Tsukuba, Jaan 1

2 Modes of non-ideal resonse (error modes) of article sizing instruments for monodiserse articles Mode 0 (Bias in concentration) Mode 1 (Bias in size) Mode 2 (Broadening) dn/dd true distribution aarent distribution n-th moment of size distribution M n D n ( dn dd ) dd M 0 Particle size, D M 1 M 2 2

3 Means of validation of size resolution At resent, we have no well-established method of validating size resolution of article measurement instruments. Nearly monodiserse articles the size disersion of which is accurately known can serve for this urose. Mode 2 (Broadening) e.g., standard deviation of the size distribution dn/dd Size resolution Particle size, D Polystyrene latex (PSL) articles 3

4 Determination of the size disersion of nearly monodiserse articles It should be noted that every sizing method cannot escae its own broadening, the effect of such broadening on aarent size disersion must be first evaluated and then subtracted. The method we roose: [Ste 1] Exerimentally evaluate the transfer function of a differential mobility analyser (DMA). Martinsson, B. G., Karlsson, M. N. A., and Frank, G. (2001), Aerosol Sci. Technol., 35, Karlsson, M. N. A., and Martinsson, B. G. (2003), J. Aerosol Sci. 34, [Ste 2] Use this DMA to evaluate the size disersion of PSL articles. Knutson, E. O., and Whitby, K. T. (1975b), J. Aerosol Sci., 6, Ehara, K., Mulholland, G. W., and Hagwood, R. C. (2000), Aerosol Sci. Technol., 32,

5 Tandem DMA (TDMA) method for evaluation of DMA transfer function dn/dz Mobility dist. z dn/dz DMA-A Mobility dist. z DMA-B CPC (condensation article counter) DMA sectrum N(V) V Proerties of the two DMAs cannot be differentiated. It is assumed that the two DMAs have the same transfer function. 5

6 Three-way comarison of three DMAs [Ste 1] (tri-tdma method) N AB (V) (1) DMA-A DMA-B CPC V N BC (V) (2) DMA-B DMA-C CPC V N CA (V) (3) DMA-C DMA-A CPC V Proosed by Martinsson et al., (2001). Aerosol Sci. Technol., 35, The transfer function of an individual DMA can be evaluated. 6

7 Non-ideal behaviours of DMA transfer function (z ) Area, S = S /S = z c /z c = z/z (Mode 0) (Mode 1) (Mode 2) ideal actual S z c z c z z z Parameters introduced by Martinsson et al.,(2001) Loss arameter: = S /S ( 1) Broadening arameter: = z/z ( 1) ( Shift arameter: = z c /z c introduced by us ) 7

8 Setu for tri-tdma exeriment Neutralizer NaCl solution from Aerosol Generator Am Sheath Clean air DMA-1 Q a 1.0(L/min) 1.0 Static Mixer Q a 2.0 Q a 1.0 Sheath Q a 1.0 CPC-1 CPC(TSI 3010) DMA-2 Q a 1.0 CPC-2 Vacuum Excess 8

9 Tri-TDMA sectra - an examle Normalized article counts Q c = 16 L/min, Q a = 1 L/min Size secified by the uer DMA = 100 nm A B B C C A Relative electrical mobility 9

10 Broadening arameters of three DMAs Q c deendence for Q a = 1 L/min at 100nm 1.00 Broadening arameter, μ DMA-A DMA-B DMA-C Sheath air flow rate, Qc (L/min) 10

11 Evaluating size disersion of PSL articles [Ste 2] - Mobility analysis of PSL articles by a DMA with known broadening arameter - CPC Particle count (#/cm3) N(V) DMA Voltage (V) PSL: JSR Stadex SC-010-S (100 nm) DMA: TSI 3081 ( 0.95) Qa = 1 L/min, Qc = 15 L/min N( V ) G( D ) ( Z ; V ) dd Exerimental sectrum Size distribution Transfer function 11

12 Inversion of the integral equation National Institute of Advanced Industrial Science and Technology Evaluating size disersion of PSL articles - Moment method - N( V ) G( D ) ( Z ; V ) dd is an ill-osed roblem, but the size distribution moment m n can be calculated, with an aroriate choice of k, from m D n n G( D )dd G( D ) dd V x k k N( V )dv ( x)dx z z V ) ( z ; V ) (normalized moment) c ( The standard deviation of G(D ) is then determined by 1, 2) : transfer function with normalized argument m m ) Knutson, E. O., and Whitby, K. T. (1975b), J. Aerosol Sci., 6, ) Ehara, K., Mulholland, G. W., and Hagwood, R. C. (2000), Aerosol Sci. Technol., 32,

13 of two 100 nm PSL articles Standard deviation (nm) JSR SC-010S NIST SRM1963a Sheath flowrate Qc (L/min) evaluated with TSI 3081 (Qa = 1 L/min, = 0.95 ~ 0.98) CPC article count (#/cc) TSI 3081, Qa=1 L/min, Qc=15 L/min NIST SRM 1963a JSR SC-010S DMA Voltage (V) Raw DMA sectra for JSR SC-010S and NIST SRM 1963a 13

14 Develoment of size disersion standard -Summary - It is ossible to determine the size disersion of nearly monodiserse articles in the following two stes: [1] Broadening arameter of a DMA is first determined by the tri-tdma method. [2] The standard deviation of PSL size distribution,, is then determined by the moment method using this DMA. Uncertainty analysis of has to be conducted to use these articles as 'certified' size disersion standards. 14

15 Calibration services rovided at AIST Mode 0 (Bias in concentration) Mode 1 (Bias in size) Mode 2 (Broadening) dn/dd true distribution aarent distribution Particle size, D Detection efficiency of CPCs Size disersion standards currently under develoment Particle size of standard articles 15

16 The rimary standard of number concentration of airborne articles Faraday-cu aerosol electrometer Insulation between the electrodes Triaxial connector Size classified, +1- charged articles Current Measurement Flow rate Measurement Shield Case Faraday Cu Relative Exanded Uncertainty (k = 2) ( % ) Flow rate = 1 L/min cm cm e+2 1e+3 1e+4 1e+5 Particle Concentration (cm -3 ) oster resentation: Jaan's National Standard for Aerosol Particle Number Concentration, (Sakurai, H., Saito, K., & Ehara. K.) 16

17 The rimary standard of article size (100 nm - 1 m) - Electro-gravitational Aerosol Balance (EAB) Millikan tye cell time 0 time t h f e : electrostatic f e > f g V f e = f g f g : gravitational f e < f g charged monodiserse articles Exanded uncertainty (k = 2) = 0.66 nm for 100 nm PSLs Reference: Ehara, K.,, Takahata, K., and Koike, M., Aerosol Sci. Technol., 40, (2006) 17

18 Calibration of article size, nm Relative measurement by differential mobility analysis 100 nm reference articles calibration EAB (absolute method) DMA (relative measurement) 10 nm 30 nm 100 nm 1 m Use of the DMA-moment method to determine number average diameter Use of an electro-sray aerosol generator U = 2.0 nm (k = 2) for 30 nm 18

19 Possible traceability scheme for SMPS Standard article manufacturer NMI Primary standards of article size & size disersion Calibration Standard articles NMI Primary standard of article number concentration Calibration Key comarison Key Comarison missing Other NMIs International standardization missing Standardized rocedure Standardized rocedure Standardized rocedure Standardized rocedure Validation Standard articles Calibration/Validation Calibration DMA Particle charger Measurement AE/CPC CPC SMPS Calibration service rovider End user dn dd Target aerosol D 19

20 Conclusions For comlete traceability of article measurement instruments, we need to calibrate/validate number concentration, article size, size resolution. Size disersion standard for validation of size resolution can be realized in two stes: 1) Evaluation of DMA transfer function by the tri-tdma method. 2) Determination of (standard dev. of size distribution) of nearly monodiserse articles by the moment method. Missing links: Platform for international comarison in the CIPM MRA scheme A means for validation of article chargers (for SMPS traceability) 20