Cambridge Particle Meeting

The Traceable Calibration of Condensation Particle Counters

Hans-Georg Horn+, Oliver F. Bischof+, Wei Liu++

+TSI GmbH, Aachen, Germany++TSI Incorporated, Shoreview MN, USA

Cambridge Particle Meeting - 2006

Why calibrate CPCs?

Condensation particle counters (CPCs) have been used to measure number concentration of ultrafine particles for almost 30 years

As part of scanning mobility particle sizer (SMPS™) to measure size distributions as well

Currently new regulations involving particle number concentration measurements are discussed Hence, calibration of CPCs using a traceable method to ensure proper performance is required

Method to calibrate smallest particle size detection limit, counting efficiency & concentration linearity

What is a Calibration?

Calibration:2)

The set of operations that establish, under specific conditions, the relationship between values for quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards.

2) International Vocabulary of Basic and General Terms in Metrology, 2nd ed.,BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML, International Organization for Standardization (ISO), 1993 (VIM), 6.11

Calibration Method

The calibration method at TSI follows the well-known ‘primary absolute calibration’ method first described by leading aerosol scientists B. Liu and D. Pui in 1974 3)

3) Liu, B.Y.H. and D.Y.H. Pui [1974]. A Submicron Aerosol Standard and the Primary Absolute Calibration of the Condensation Nucleus Counter.J. Coll. Int. Sci., Vol. 47, pp. 155–171

Calibration Setup

Compressed Air Filtered Air

Supply

Electrospray Aerosol

Generator

Electrostatic Classifier with

nano-DMAAerosol

Electrometer

Test CPC1.5 L/min

Make-up Air

1.5 L/min

Po-210 Neutralizer

Flow Meter

FlowSplitter

CO2

Electrospray AG generates (emery oil) particlesDMA selects singly-charged, monodisperse particles of known size Monodisperse aerosol mixes with filtered air & splits equally into aerosol electrometer and CPCCounting efficiency: ratio CPC / electrometer readings

Calibration Details

This presentation discusses calibration results for standard TSI model 3010 and 3010D (PMP) CPCs.

Smallest particle size detection limit & Counting efficiency

Concentration linearity

CPC intercomparison

Traceability of Calibration Method

Traceability of the CPC calibration method depends on:

The ability of generating singly-charged, monodisperse particles of known size

The ability of measuring particle concentration accurately using a reference aerosol detector

Monodispersity of Particles

Step 1: Particles generated by electrospray(22 nm, GSD = 1.46) Step 2: Particles generated by

electrospray and selected by DMA (22 nm, GSD = 1.04)

Electrospray-generated, DMA-selected particles: 50 nm: GSD = 1.0490 nm: GSD = 1.11

Traceability – DMA

VL2)rrln()]qq(2/1q[

Z 12mptp π

+−=

Flow rates (qt=qs+qp) – NIST traceable flow metersSheath flow rate (qs)Polydisperse/Monodisperse aerosol flow rate (qp = qm)

Geometric parameters – NIST traceable bore gage, micrometer, and caliper

r1 / r2 = inner / outer electrode radiusL = characteristic length between aerosol inlet/outlet slits

Voltage on center electrode (V) – calibrated with NIST traceable kilovolt divider

In a cylindrical DMA, Zp of selected particles is

Aerosol Electrometer

where: N = particle number concentrationV = electrometer voltage reading (IR)e = unit charge, 1.602 x 10-19 CR = resistance of resistornp = number of charges per particleqe = air flow rate

ep qnReVN

⋅⋅⋅=

InducedCharge Flow(Current)

Particle Filter

Charged Aerosol Particles

I

Air Flow

Resistor

VR

Traceability – Aerosol Electrometer

Unit charge (e) – is a constant (1.602 x 10-19 C)Resistor (R) – 1% precision, measured by manufacturer using NIST traceable standard Particle charge (np) – verified to be unity (1.0) by SMPSFlow rate (qe) – NIST traceable flow meter

Aerosol Electrometer Inlet Losses

Particle losses as a function of particle size and flow rate

0.00%

1.00%

2.00%

3.00%

4.00%

5.00%

6.00%

7.00%

1 10 100

Particle Size (nm)

Diffu

sion

Los

s (%

)

1 l/min3 l/min5 l/min

Laminar flowTube length 10 cmT = 293 KP = 101.3 kPa

Inlet tubing to the Faraday cage must be kept as short as possible or losses must be quantified and corrected.

Calibration Details

Smallest Particle Size & Counting EfficiencyDepending on CPC model, 10 – 14 particle sizes below 100 nm used for counting efficiency curve Particle concentration < 104 P/cm3

CPCs 3010, 3010D (or other models) can be tested simultaneously• Model 3776 is tested one by one due to low concentration at

their smallest particle sizesTo eliminate need for diffusion loss correction• Equal tube lengths from flow splitter to electrometer & CPCs• Equal flow rates for electrometer & CPCs

CPC concentrations corrected for coincidence

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 10 100Particle Size, nm

Cou

ntin

g Ef

ficie

ncy,

%SN2311_StandardSN2454_StandardSN2460_StandardSN70419349_StandardSN70419353_Standard

Results: Counting Efficiency of 3010

SN2311_S SN2454_S SN2460_S SN70419349_S SN70419353_S Size RangeD10, nm 7.2 6.5 6.4 6.9 6.5 6.8 ± 0.4D25, nm 8.3 7.6 7.5 8.0 7.4 7.9 ± 0.5D50, nm 9.9 9.1 9.1 9.7 8.9 9.4 ± 0.5D75, nm 11.9 11.0 11.0 11.7 11.1 11.4 ± 0.4D90, nm 14.0 13.0 13.0 13.8 13.6 13.5 ± 0.5

Standard 3010 CPC

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 10 100Particle Size, nm

Cou

ntin

g Ef

ficie

ncy,

%SN2454_ModifiedSN2460_ModifiedSN70419351_ModifiedSN70419352_ModifiedSN70419354_ModifiedSN2311_StandardSN2454_StandardSN2460_StandardSN70419349_StandardSN70419353_Standard

PMP Range

Modified 3010D CPC

SN2454_M SN2460_M SN70419351_M SN70419354_M SN70419352_M Size Range PMP RangeD10, nm 15.9 16.2 15.8 16.4 16.5 16.1 ± 0.4 16 ± 1

18 ± 223 ± 337 ± 4

D25, nm 17.9 18.2 17.9 18.5 18.4 18.2 ± 0.3D50, nm 21.3 21.6 21.5 22.1 21.9 21.7 ± 0.4D90, nm 34.9 35.3 33.4 33.9 34.8 34.3 ± 1.0

Results: Counting Efficiency of 3010D

Standard 3010 CPC

Counting Efficiency 3010D

0%10%20%30%40%50%60%70%80%90%

100%110%

1 10 100Particle Diameter, nm

Cou

ntin

g Ef

ficie

ncy

705070037050700470507005705081457050814670515208705170757051707670517077705242097052421070524211

CPC Efficiency

PMP Lower Limit (nm)

PMP Mid Diameter (nm)

PMP Upper Limit (nm)

10% 15 16 17 25% 16 18 20 50% 20 23 26 90% 33 37 41

Counting Efficiency Results for Twelve 3010D Production CPCs.

Concentration Linearity

Concentration LinearitySetup for concentration linearity response 4)

50 nm particles chosen for ~100% counting efficiency for CPCSix to ten concentrations levels, depending on CPC model• Higher concentrations reduced by dilution bridge

Equally spaced from 0 - 104 P/cm3 (CPC 3010) and 2,000 to 300,000 P/cm3 (UCPC 3776) respectivelyReference instrument• Aerosol Electrometer 3068A (for 3776 only for validation)

- From April 2006 new aerosol electrometer model 3068B

4) Liu, W., B.L. Osmondson, O.F. Bischof and G.J. Sem (2005). Calibration of Condensation Particle Counters. SAE Paper No. 2005-01-0189.

Linearity Response of 3010 & 3010D

Slope = 0.953 to 0.973R2 > 0.9988

2454: y=0.9569x, R2=0.99912460: y=0.9676x, R2=0.9991

70419349: y=0.9731x, R2=0.998870419353: y=0.9532x, R2=0.998870419351: y=0.9693x, R2=0.998870419352: y=0.9670x, R2=0.998870419354: y=0.9668x, R2=0.9988

0

2000

4000

6000

8000

10000

12000

0 2000 4000 6000 8000 10000 12000

Electrometer Reading, particles/cm3

CPC

Rea

ding

, par

ticle

s/cm

3

2454_30102460_301070419349_301070419353_301070419351_3010D70419354_3010D70419352_3010D

Linearity of 3010D (Production)

70515208y = 1.02x

R2 = 0.9967

70507003y = 0.9666xR2 = 0.9997

70507004y = 0.9508xR2 = 0.9999

70507005y = 0.9713xR2 = 0.9997

70508145y = 0.9593xR2 = 0.9997

70508146y = 0.9657xR2 = 0.9997

70517076y = 0.968x

R2 = 1

70517077y = 0.9757x

R2 = 1

70524209y = 0.9804xR2 = 0.9996

70504210y = 0.9822xR2 = 0.9996

70524211y = 0.9861xR2 = 0.9997

70517075y = 0.9667xR2 = 0.9999

0

2000

4000

6000

8000

10000

12000

14000

0 2000 4000 6000 8000 10000 12000 14000Electrometer Reading, particles/cm3

3010

D C

PC R

eadi

ng, p

artic

les/

cm3

705070037050700470507005705081457050814670515208705170757051707670517077705242097052421070524211

Linearity Response of Twelve 3010D Production CPCs.

Contact

For More Information

TSI GmbHNeuköllner Str. 4

52068 Aachen, Germany

Tel.: +49-241-5 23 03 0Fax: +49-241-5 23 03 49

Email: particle-europe@tsi.comhttp://particle.tsi.com