Liu Junjie, Zhang Wenge, Song Xiaoping

Division of Nano metrology and Materials Measurement

National Institute of Metrology, China

Traceability research activities in the field of airborne particle number/ mass concentration measurement

• Division of Nano Metrology and Materials Measurement

Advanced Materials Laboratory

Focusing on the accurate measurement of particle characteristics， - Developing the traceable instruments and calibration procedures for particle number concentration and particle mass concentration. PM10/PM2.5 calibration standards particle counting in airborne calibration standards -Traceability study of particle size measurement methods in nano- and micro- scale meter, for example, SEM, TEM, AFM, DLS, NTA and DMA methods -Particle counting in liquid

Nanometrology Laboratory

Physical Chemistry Laboratory

Particle Measurement

Chemical composition analysis

particle mass concentration measurement

/ / /

Accurate measurement of PM2.5 mass concentration and calibration of

automatic PM2.5 monitors

Automobile exhaust particle number concentration measurement

Calibration of PM2.5 sampler/ monitor

Calibration of PM2.5 seperators

PM2.5 Calibration Plan

Standard sampling method

Next Step Condensation particle counter calibration

• Gravimetric standard for PM 2.5 mass concentration, development of calibration instrument for PM2.5 sampler (finished)

• Development of calibration instrument for PM2.5 impactors, National metrology calibration specification for PM10/PM2.5 impactors (finished)

• development of calibration instrument for online PM2.5 monitors (undergoing) • Condensation particle counter (CPC) calibration (undergoing)

Research activities in PM2.5 calibration(2013~2017)

Gravimetric standard for PM 2.5 mass concentration

A calibration instrument /standard have been designed and developed. • auto sampling • Membrance auto-balance and auto-weighting

Gravimetric standard for PM 2.5 mass concentration

Particle aerosol

PM2.5 impactor

Membrane

Flow controller

Pump

Barometer

Therometer

Balance

Therometer

Displayer/recorder

Uncertainty is less than 3%,k=2

Cut-point calibration standard for PM2.5 impactor/seperator

Cut point:

D50=10±0.5µm (PM10)

D50=2.5±0.2µm (PM2.5)

Impactor calibration, establish the curve of penetration and aerodynamic diameter

Series particle size standard polystyrene particles with nominal value (1.0— 4.0) um were prepared by dispersion polymerization method Standard deviation of particle size distribution is less than 3.0%

Cut-point calibration standard for PM2.5 impactor

Particle counting in airborne (particle number concentration ) Optical particle counter (OPC) and Condensation particle counter (CPC) calibration

China: GB18352.5-2013 limits and measurement methods for emission from light-duty vehicles standard was implemented.

EU: Euro 5 emissions regulations for light diesel vehicles and Euro 6 emission regulations for heavy-duty diesel vehicles

2. Characterization of exhaust particulate emissions for road vehicles

Particle counting efficiency calibration for OPC and CPC

Optical particle counter OPC

condensation particle counter CPC

Faraday-cup aerosol electrometer FCAE

Electrical current

In OPC calibration field, a widely recognized OPC traceability chain has already been established and described in several ISO document, where, OPC should be calibrated by CPC, if it has already been calibrated by Faraday cup aerosol electrometer (FCAE). Using this calibration method, it is possible to make the particle number concentration result of OPC trace to an international recognized primary unit-- electrical current.

1. Clean room classification monitoring In ISO 14644-1, the air cleanliness in cleanrooms is classified according to the particle number.

Calibration of Faraday-cup aerosol electrometer

y = 0.9321x + 0.1104 R² = 1

0102030405060

0 20 40 60

resp

onde

nt e

lect

rical

cu

rren

t of F

C /f

A

Standard electrical current /fA

respondent electrical current of FCAE is well calibrated, and the calibration uncertainty is less than 1% k=2 (>10fA).

Respondent electrical current calibration

Particle counting in airborne (particle number concentration)

eQI

etQqC ==

Calibration method for Faraday-cup aerosol electrometer (FCAE) was developed, by comparing the respondent electrical current of FCAE with reference electrical current.

Electromagnetic shielding box

resistance

FCAE Controller

Calibration of counting efficiency

In the range of （3600~39000）particles/cm3, uncertainty of counting efficiency calibration is less than2.5%（k=2）

Zero calibration, flow rate calibration, respondent electrical current calibration

FCE

R

eQII

etQqC

)( 0−== %100×=

CCFCE

FCEη

Condensation particle counter calibration

%100)202()153()101(

)101(

321

11 ×

++=

CCCC

φ

%100)202()153()101(

)153(

321

22 ×

++=

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φ

%100)202()153()101(

)202(

321

33 ×

++=

CCCC

φ

∑=

××××

=3

1pPFCE

FCE

CPCCPC P

CfC

φηβ

η

Particle counting in airborne (particle number concentration)

Correction for multiply-charged effect

In CPC counting efficiency calibration, a differential mobility analyzer was used to achieve monodisperse particle surface with only single charge. But actually, in the aerosol from the outlet of DMA, some large particles surface with multiply charges might be involved, because those large particles have the same electrical mobility in DMA chamber as single-charged particles. And if this multiply-charged effect in aerosol is actually existed, particle number concentration recorded by FCAE would not represent the real aerosol particle concentration, because the respondent electrical current caused by multiply-charged large particles will not be proportional to the aerosol concentration. On account of this, in CPC counting efficiency calibration multiply-charged effect should be corrected,

stable and single-charged particles aerosol were firstly produced by using DMA, and then after through a flow splitter, particles aerosol is equivalently separated into two ways, and pumped into FCAE and CPC separately , where FCAE counting efficiency has already been well calibrated.

CPC and calibration

Calibration points 1 2 3 4 5

/(particles/cm3) 6937 7013 6952 6915 6845

/(particles/cm3) 6770.7 6844.9 6977.2 6749.2 6680.9

Dilution factor f 1 2 5 10 20

CCPC/(particles/cm3) 6689 3380 1373 670 328

CPC counting

efficiency/(%) 98.79 98.76 98.39 99.27 98.19

FCEC

Particle counting in airborne (particle number concentration)

Condensation Particle Counter

（CPC）

Optical

Particle Counter (OPC)

10 nm 100 nm 1000 nm

Aerosol Electrometer

(AE)

1 cm-3

10 cm-3

100 cm-3

1000 cm-3

10000 cm-3

1 nm

Part

icle

Con

cent

ratio

n

Particle Size

T-tube Designed dilutor Dilutor from commercial

FCAE

CPC dilutor

splitter

Using calibrated FCAE as top standard of particle number concentration, and by comparing the results of FCAE and under-tested CPC, counting efficiency of CPC can be verified and calibrated. In the range of (200~16000) /cm3, uncertainty of CPC calibration result is about 5% (k=2).

OPC calibration

Calibration points 1 2 3 4

CCPC/f（particles/L） 1575.8 5182.4 16121.9 31228.6

OPC value（particles/L） 1478.9 4980.1 15545.6 29462.1

Particle counting in airborne (particle number concentration)

Condensation Particle Counter

（CPC）

Optical

Particle Counter (OPC)

10 nm 100 nm 1000 nm

Aerosol Electrometer

(AE)

1 cm-3

10 cm-3

100 cm-3

1000 cm-3

10000 cm-3

1 nm

Part

icle

Con

cent

ratio

n

Particle Size

dilutor

splitter

Filter

Using calibrated CPC as standard of particle number concentration, and by comparing the results of CPC and under-tested OPC, counting efficiency of OPC can be verified and calibrated. In the range of (1500~30000) particles/L, uncertainty of OPC calibration result is about 8% (k=2).

summarize

• PM2.5 sampler and monitors comparison. • Increasing the accuracy of CPC calibration results, especially in the

low particle number concentration range (less than 100/cm3). • Carrying out CPC comparison.

Thank you very much