Da-Ren (Daren) Chen (陳大仁)

Floyd D. Gottwald, Sr. Chair and Professor

Particle Lab., Department of Mechanical & Nuclear Engineering

Virginia Commonwealth University

401 West Main Street, Richmond, VA, 23284, USA

Chang jiang Chaired Professor (长江学者), School of Environment

Tsinghua University, China;

Development of Miniature Sizers for

Ultrafine Particle Measurements

Particle Lab, VCU

Outline

Introduction and Overview

Development of key components for UFP sizers

Integration of miniature electrical particle sizers

Conclusion

Particle Lab, VCU

http://www.aerasense.com/index.php?pageID=6

Figure 1 Idealized particle size distribution

USEPA: Air quality criteria for particulate matter (Final Report, Oct 2004). U.S. Environmental Protection Agency, Washington, DC, EPA 600/P-99/002aF-bF; 2004.

Introduction – UFP in Ambient Air

o Ultrafine Particles (UFPs), Dp < 100 nm

o Source: natural sources (e.g. gas-to-particle

conversion, forest fires, viruses, etc.)

combustion engine, metal fumes (e.g. smelting,

welding), vehicle exhaust, nanoparticle industry,

etc.

Ultrafine particle fine particle (PM2.5) PM10 TSP

Particle Lab, VCU

http://www.tesa-clean-air.com/eng/fine_dust_particles

Introduction – UFP Health Effect

From Geiser and Kreyling, Particle Fibre Toxicol, 2010, 7:2

o Nanomaterial (10 to 50 nm) could easily enter the human body and deposit in

the alveolar region of a human lung, even entering in the blood stream and

being transported to vital organs (Kreyling et al., 2002; Takenaka et al., 2001; Oberdörster et

al., 2004; Paur et al., 2011).

o UFPs are particularly relevant to pulmonary diseases, cancer and mortality

because of their higher diffusion coefficient and greater accumulation

ability (Hoek et al, 2002; Oberdörster et al, 2005; Bräuner et al, 2007; Stewart et al, 2010).

o The increased asthma prevalence has been found to

often occur in the area with high UFP levels in

ambient air or high motor vehicle traffic density

and residence community in close proximity to

freeways (Samet et al, 2000; Holguin, 2008; Salam et al, 2008;

Patel and Miller, 2009).

Particle Lab, VCU

Review of UFP Measurement (1)

Number concentration

• Condensation Particle Counter (CPC)

Size distributed number concentration

• ELPI, SMPS, FMPS, EEPS, DMS

Size distributed mass concentration

• Nano-MOUDI

Surface area

• Nanoparticle Surface Area Monitor (NSAM)

Composition

• Aerosol Mass Spectrometer (AMS)

UFP

Measurement

o The technique based on particle electric mobility has

been applied in aerosol community to characterize

size distribution of ultrafine particles

Detector (CPC

/ Aerosol

electrometer)

Aerosol

Charger Differential

Mobility

Analyzer (DMA)

Particle Lab, VCU

Review of UFP Measurement (2)

FMPS SMPS DMS

o Existed instruments to characterize UFPs are mainly designed for scientific

studies in the laboratories and are often expensive in price, bulky in package

and heavy in weight.

Particle Lab, VCU

Instrument Dimensions / Weight Price

TSI Nanoscan 3910 45 cm x 23 cm x 39 cm

< 8kg without batteries;

< 9kg with 2 batteries $~30K

Kanomax portable

aerosol mobility

spectrometer (PAMS)

23 cm x 23 cm x 15 cm

4.5 kg

Naneum Nano-ID

PMC500

30 cm x 33 cm x 26 cm

6.25 kg

Grimm Mini wide range

aerosol spectrometer

(WARS)

34 cm x 31 cm x 12 cm

7.6 kg $30-40K

o Portable Aerosol Sizers developed based on particle electric mobility

o Large in size, heavy and high

cost

o Single-alone operation

o Not easy to be networked (a

much desired feature for

modern UFP monitoring.)

Review of UFP Measurement (3)

A more compact and cost-

effective UPF sizers and

wireless mesh network using

eUFP sizers as the nodes are

needed in the modern UFP

monitoring (i.e., spatio-temporal

monitoring).

Particle Lab, VCU

Potential Applications

for Miniature Ultrafine/Fine Particle Sizers

• Air pollution and quality study

• Vertical profiling of ultrafine particles

• Indoor air quality monitor

• Early fire detection (office and hospital buildings)

• Industrial hygiene and worker protection

• Epidemiology study

• Identification of particulate emission sources

• Nano-manufacture process control (nanopowders, pharmaceutical products..)

• Pharmaceutical R&D

• and more…..

Particle Lab, VCU

Motivation of Our Development of mini- Sizers

o To enable the spatio-temporal distribution measurement and

personal exposure monitoring

miniature aerosol sensor/sizer:

(1) cost-effective;

(2) light in weight;

(3) small in package;

(4) easy in use;

(5) having the feature of networking

Particle Lab, VCU

A miniature electrical ultrafine particle sizer

• Aerosol charger

• Unipolar/bipolar particle chargers

• Electrical mobility classifier

• Precipitator/EAA/DMA

• Particle concentration detector

• Faraday cage with pre-amp or CPC

• Data inversion scheme

Particle Lab, VCU

Miniature Unipolar Aerosol Charger

Aerosol

Inlet

Corona

Voltage Aerosol

Outlet

Ion-driven

Voltage

1.0"

0.5"

Particle Lab, VCU

Extrinsic Charging Efficiency of mini- Charger

Particle Size (nm)

3 4 5 6 7 8 10 15 20 25 35 50 75 100

Ext

rin

sic

Ch

arg

ing

Effic

ien

cy (

%)

0

20

40

60

80

100

Bipolar-Fuchs

Mini-charger 0.3 LPM

Mini-charger 1.5 LPM

Buscher et. al., 1994

Mini-charger, with a simple and very compact design, is capable of providing much better charging efficiency than bipolar charging

In 1.5 lpm flowrate, its charging efficiency can even be compared with Buscher’s charger with a much more complicated design

Particle Lab, VCU

o Overall size: 2.2" (5.59 cm) × 1.25" (3.18

cm) × 0.69" (1.75 cm) (L × W × H)

o Charging zone spacing: 0.125" (0.32 cm)

o Tungsten wires of 50 µm in diameter

Mini-plate Particle Charger: Design

Brass Teflon

Stainless steel

A B

C D

Aerosol Out

Aerosol In

Charging zone

Wires in the corona

discharge zone

Perforated plate

Schematic diagram of prototype DC-corona-based mini-plate charger

Particle Lab, VCU

Mini-plate Particle Charger: Experimental Evaluation

Test Aerosol: NaCl, 10 – 200 nm

Key aspects of charger performance:

(1) intrinsic/extrinsic charging

efficiency;

(2) charge distribution on aerosol

Charger performance depends on:

Charger configuration

Aerosol flowrate

Corona current

Particle size

A

B D

C

Particle Lab, VCU

Mini-plate Particle Charger: Optimization of charger configuration

95.56% 97.71% 92.92% 91.19%

99.12% 99.50% 93.85% 95.19% 96.03% 97.13% 96.84% 96.50%

57.65% 59.35%

40.77%

62.96%

42.98%

35.28% 39.38%

34.09% 37.54%

31.83%

42.58%

52.37%

0%

20%

40%

60%

80%

100%

120%

1 2 3 4 5 6 7 8 9 10 11 12

Ch

arg

ing

Eff

icie

ncy

%

In % EX %

Corona discharge at current of 2 µA

Corona discharge at current of 1 µA No corona discharge

o 40 nm NaCl nanoparticle

o 0.3 lpm aerosol flowrate

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Evolution of Mobility Classifier Development

(a) Zeroth order

(b) 1st order

(c) 2nd order

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Miniature Disk-type Electrostatic Precipitator

(Aerosol Classifier in the zeroth order)

0.5

45 * 0.025

HV

0.84

1.750.1

0.05

Metal

Insulation

Material

Particle Lab, VCU

Mini-disk Electrical Aerosol Classifier (mini-disk EAC)

(Aerosol Classifier in the 1st order)

Particle Lab, VCU

Mini-plate Differential Mobility Analyzer (mini-plate DMA)

(Aerosol Classifier in the 2nd Order)

Delrin

Sheath flow out

/Excess flow

Teflon

Stainless steel

Aluminum

Polydisperse

aerosol flow in

Monodisperse

aerosol flow out

Sheath flow in

High voltage connection

Ground

Flow

laminarizer

(a)

Aerosol

entrance slit

Aerosol exit slit

(b)

Aerosol

entrance slit

Aerosol

exit slit

Flow

laminarizer

Polydisperse aerosol

flow in

Monodisperse

aerosol flow out

Particle Lab, VCU

Mini-plate DMAs V1 V2 V3

Classification Zone

Aerosol slit opening Overall Size

Length Width Height Length Width Height

V1 1 39/64"

(40.88)

1"

(25.4)

(2.06)

1/2" × 1/32"

(12.7 × 0.79)

3 7/32"

(81.76)

1 3/4"

(44.45)

13/16"

(20.64)

V2 1 13/32"

(35.72)

1"

(25.4)

1/8"

(3.18)

1/2" × 3/32"

(12.7 × 2.38)

3 7/8"

(98.43)

1 3/4"

(44.45)

7/8"

(22.23)

V3 2 1/16"

(52.39)

1 1/2 "

(3.81)

(2.11)

1 1/8" × 1/32"

(28.58 × 0.79)

4 7/8"

(123.83)

2 7/16"

(61.91)

21/32"

(16.67)

Key dimensions in mini-plate EAA/DMAs, units: in (mm)

Particle Lab, VCU

0

150

300

450

600

0

50

100

150

200

250

300

10

Vc

/ V

Dp / nm

Mini-plate DMA: Sizing accuracy (1)

0

500

1000

1500

2000

2500

3000

3500

4000

10 100

Cen

tral

Vo

ltag

e (V

c) /

V

Dp / nm

Experimental Vc Calculated Vc without correction

𝑍𝑝,𝑐 = 𝑄𝑠ℎ ℎ

𝐿 𝑊 𝑉

The deviation between the experimental

and calculated voltages at the given

particle sizes is not negligible.

Particle Lab, VCU

Mini-plate DMA: Sizing accuracy (2)

ɳ = -0.6866β + 1.1645

0.60

0.70

0.80

0.90

1.00

1.10

1.20

0.00 0.05 0.10 0.15 0.20 0.25

ɳ

β=Qa/Qsh

𝑍𝑝,𝑐 = ɳ 𝑄𝑠ℎ ℎ

𝐿 𝑊 𝑉

The relationship between ɳ and β is linear.

It is further found that the voltage needed for

classifying particles with a given electrical

mobility varied when varying the aerosol and

sheath flowrates.

Particle Lab, VCU

0

150

300

450

600

0

50

100

150

200

250

300

10

Vc

/ V

Dp / nm

Mini-plate DMA: Sizing accuracy (3)

0

500

1000

1500

2000

2500

3000

3500

4000

10 100

Cen

tral

Vo

ltag

e (V

c) /

V

Dp / nm

Experimental Vc Calculated Vc with correction

o The ±2.5% for the voltage deviation might be

attributed to the accuracy in the flowrate control and

measurement as well as the possible 3D flow effect

Particle Lab, VCU

y = 1.58E-19x

0

5E-15

1E-14

1.5E-14

2E-14

2.5E-14

3E-14

3.5E-14

4E-14

0.00E+00 1.00E+05 2.00E+05C

urr

ent

/ A

NQa / #/s

Mini- Faraday Cage with pre-amp

Charged

Particle In

Flow Outlet

Connected to

Electrometer

𝑰 = 𝑛 𝑒 (𝑵𝑄𝑎)

where, I is the current measured by electrometer; ne is the charge carried by

particles; Qa is aerosol flow rate and N is the particle number concentrations.

y = 2148.3x

0

20

40

60

80

100

120

0 0.02 0.04 0.06

fA

V

Particle Lab, VCU

Prototype Portable Fine Particle Sizer

(portable FPS; Funded by NASA)

Aerosol flowrate: 0.7 lpm

2009 R&D 100 Award

(R&D magazine)

Particle Lab, VCU

Miniature Electrical Ultrafine Particle Sizer (mini- eUPS)

(funded by US EPA)

Key components

mini- eUPS mini-plate DMA/EAA

mini-Faraday cage with pre-amp

Features included

mini-plate aerosol charger

Portable, Cost-effective,

Energy efficient

Real-time on particle size distribution, temperature,

Humidity, GPS, pressure and Altitude

Self diagnosis Wireless networking

Wireless data transmission Data hubbing

Particle Lab, VCU

Prototype mini- eUPS

Final package: 7.5" (L) × 5.5" (W) × 4.5" (H)

Weight: < 3.5 lb

Mini-plate charger with

temperature/humidity sensors

Mini-plate DMA

Mini-Faraday Cage

Electrometer

Circuit

Aerosol flow pump

Sheath flow pump

HEPA filters

Raspberry Pi with

touch screen

Particle Lab, VCU

Performance of Prototype mini eUPS

Classifier

(TSI 3080)

UCPC

(TSI 3776)

Laminar

Flow Meter

Compressed Air Atomizer

Diffusion Dryer

Mini-eUPS

10 1000

1x105

2x105

3x105

4x105

5x105

dN

(#

/cc)

Dp / nm

Mini e-UPS

SMPS

Particle Lab, VCU

Conclusion Remarks

• Electrical mobility based particle analyzers are powerful tools for the

characterization of particles in fine and ultrafine size ranges

• Miniaturization of electrical mobility particle sizers have been realized for

measuring the spatial and temporal size distribution of fine and ultrafine particles

• Portable FPS (with CPC) and mini- eUPS (with aerosol electrometer) have been

assembled and evaluated using the lab-generated particles.

Particle Lab, VCU

Thank you for your attention

Acknowledgement

The authors are grateful for the financial support provided by NASA Glen Research Center

and STAR program, US EPA (Grant # 83513201).

COI statement

Chen, one of the authors, holds the licensed IP, which is similar in name, but unrelated in

configuration, to this project.