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Instrumentation for Ambient UltrafineParticle Measurement
historic perspectivesand
recent developments----
Susanne HeringAerosol Dynamics Inc.
80x103
60
40
20
0
Ultr
afin
e P
artic
le N
umbe
r C
once
ntra
tion
(10
- 96
nm
)
80x103
6040200Total Particle Number Concentration (10 - 360 nm)
Fresno First StreetDecember 2000 - Feburary 2001R = 0.97slope = 0.71 ± 0.003 intercept = 1120 ± 90
14x103
12
10
8
6
4
2
0
Ultr
afin
e P
artic
le N
umbe
r C
once
ntra
tion
(10
- 96
nm
)
14x103
121086420Total Particle Number Concentration (10 - 360 nm)
Angiola (San Joaquin Valley farming area )December 2000 - Feburary 2001R= 0.95slope = 0.82 ± 0.007intercept = -470 ± 30
Ultrafine Particles Dominate Particle Number Concentrations
Rural and Urban Sites : Similar Relationship between Ultrafine Particle Number Concentrationsand Total Particle Number Concentrations
Simplest Indicator for Ultrafine
Particles:
Particle NumberConcentration
Bricard et al, 1976
Hering et al, 2005
1889: First Measurement of Atmospheric Particle Number Concentrations
John Aitken,
“On the Number of Dust Particles in the Atmosphere”,
Transactions of the Royal Society of Edinburgh, 1889
How Aitken’sInstrument
Worked
• Humidified air sample
• Expanded adiabatically
• Droplets formed around particles, which then settled
• Counted manually
• Repeated with dilution
lens
Receiving flask into which sample is expanded, with counting stage
filter
Sample collection flask
“The reason of the greater number of particles in the room than that found outside was due to the particles produced by the two gas flames burning in the room at the time.”
What Aitken Observed:
• 1912: Wilson Cloud Chamber
– 1929: Nobel Prize for particle physics
– Determined precise expansion ratios for avoiding homogeneous and ion-induced nucleation of particles
• 1930s: Scholz: Automated expansion for particle counting
• 1950s: Vonnegut: Automated counting by recognizing particles grow to uniform size.
1950s: Vonnegut, Automated Counting
Automated, but not continuous( condensing vapor: water )
Bricard et al, 1976
1970s: Thermally Diffusive Condensation Particle Counter (CPC)
Automated & Continuous ( condensing vapor: butanol or other alcohol )Widely used, suitable as detector for size distribution instrumentsMany models, sold by several companies
• Challenge : too small for direct optical detection
• Approach: Create region of supersaturation to activate particle growth => form droplets
• Why Supersaturation? Equilibrium vapor pressure over a droplet is greater than over a flat surface due to free energy associated with surface (surface tension)
• Kelvin Relation:
Pdroplet = Pflat surface exp( 2 σ σ σ σ v / kTρρρρ R )
Surface tension Particle radius
Can you have a Continuous, Automated Particle Counter without Butanol?
Thermally Diffusive CPCs: Operational Principle
• Saturate flow with vapor
• Flow into cold-walled tube
• Vapor condenses on particles
• Requires slowly diffusing vapor (e.g. butanol)
Saturator, 35°C Condenser, 10°C Optics Head
Thermal Diffusivity, Mass Diffusivity,air = 0.215 cm 2/s butanol = 0.081 cm 2/s
Note: diffusivity of water = 0.265 cm2/s > airDoes not work well with water
2003: Water Condensation Particle Counter (WCPC)
• Cold flow enters warm wet-walled tube
• Water vapor diffuses more quickly than flow warms
• Supersaturation, particle activation and growth occurs inside of a warm, wet walled tube.
Saturator, 20C
Saturator, 12C
Condenser, 60C
Condenser, 75C
Optics Head2003 WCPC(~5 nm) :
2004: Nano-WCPC (~2.5 nm)
Thermal Diffusivity, Mass Diffusivity,air = 0.215 cm 2/s water = 0.265 cm 2/s
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
0 1 2 3 4
Non-Dimensional Axial Position (x/UR2)
Cen
terli
ne S
atur
atio
n R
atio
WCPC Approach
Traditional Approach
Comparison of Centerline
Water Saturation
Ratios
WCPC: Inlet flow at 20°C & 100%RH, Wetted walls at 60°C
----------------------------------------------------Traditional: Inlet flow 60°C & 100%RH
Wetted walls at 20C
Water Condensation Particle Counter
Hering et al, 2005
First laminar-flow WCPC Response to Ambient Aerosols & Vehicle Emissions
Tunnel Measurements with Antonio Miguel, Arantza Eiguren-Fernandez, UCLA
1.0
0.8
0.6
0.4
0.2
0.0
Det
ectio
n E
ffici
ency
2 3 4 5 6 7 8 910
2 3 4 5 6
Particle Diameter (nm)
Ambient Aerosol (Berkeley, CA) Vehicle Tunnel Aerosol (Caldecott)
TSI-3785
0.0
0.2
0.4
0.6
0.8
1.0
0.0 0.1 0.2 0.3 0.4 0.5µ v = πα v z/Q
Rad
ial P
ositi
on, r
/R
1.92 nm, S=2.96
1.96 nm, S=2.89
2.00 nm, S=2.83
2.05 nm, S=2.76
2.10 nm, S=2.69
2.17 nm, S=2.59
2.37 nm, S=2.38
Calculated Supersaturation Profiles within the Ultrafine Water – CPC
αv = vapor mass diffusivityz = axial distanceQ = volumetric flow rate
100
80
60
40
20
0
WC
PC
-410
/WC
PC
-410
x (%
)
12 3 4 5 6 7 8 9
10 Particle Diameter (nm)
Efficiency for TSI-3786(water residue particles)
Positvely Charged Particles D50 = 2.4 nm
Negatively Charged Particles D50 = 2.1 nm
Calibration of the Ultrafine WCPC Water Residue Particles
TSI-3786
Comparison of Water CPC and TSI Ultrafine,Queen’s College, NY (Univ. at Albany, EPA Supersite)
Size-Selection
by
Electrical Mobility
Filtered room air
WCPC(TSI 3785)
TSI 3025
(ultrafine)
Compare:0.2-sec average
11-sec running average
counts/cm 3 measured below nanoSMPS(not ambient size distribution – no charging correct ion)
1.5 lpm
1 lpm
0.6 lpm
Ambient air inlet
Comparison to Butanol Ultrafine CPC with Nano-DMAParticle counts per 0.2 sec window (average over two scans)
TSI-3025: 1.1±1.0 particles (0.5cc/s)WCPC: 35 ± 6 particles (16.7 cc/s) --- much better counting statistics
In collaboration with ASRC, University at Albany
30
25
20
15
10
5
0
Par
ticle
Num
ber
durin
g S
MP
S S
can
(cm
-3)
3 4 5 6 7 8 910
2 3 4 5 6 7 8 9100
Diameter (nm)
Run 742/3/2004 18:15
WCPC-0.2sec WCPC-10sec TSI3025-0.2sec TSI3025-10sec
12
10
8
6
4
2
0
Par
ticle
Num
ber
durin
g S
MP
S S
can
(cm
-3)
4 5 6 7 8 910
2 3 4 5 6 7 8 9100
Diameter (nm)
Run 742/3/2004 18:15
WCPC-2sec WCPC-20sec TSI3025-2sec TSI3025-20sec
����������� �� ���������
200x103
150
100
50
0
Veh
icle
Tu
nne
l Pa
rtic
le C
once
ntra
tion
(#/
cm3)
1:00 PM3/1/2005
2:00 PM 3:00 PM 4:00 PM 5:00 PM 6:00 PM
Freeway Tunnel
Ultrafine Water CPC: TSI-3786 Butanol Ultrafine CPC: TSI-3025
Total Particle Number Concentrations for Traffic Em issions
Ultrafine WCPC (TSI-3786) compared to Butanol UCPC (T SI-3025)
Ambient Sampling In Riverside, CaliforniaUltrafine WCPC – 3786 & Butanol UCPC - 3025
50000
40000
30000
20000
10000
0
Indi
cate
d P
artic
le N
umbe
r C
once
ntra
tion
(#/c
m3)
9:00 PM7/25/2005
12:00 AM7/26/2005
3:00 AM 6:00 AM 9:00 AM
Pacific Standard Time
Riverside SOAR -ICAT
Water CPC TSI-3786 Butanol CPC T3025
60x103
50
40
30
20
10
0
Ultr
afin
e W
ater
CP
C (
#/cm
3)
50x103
403020100Butanol Ultrafine CPC (TSI-3025, #/cm3)
July 20 - August 14, 2005SOAR - ICAT Study, Riverside, CA
One-Minute Data
One-to-One Lineslope=1.065, R=0.993
2005: Micro-Environmental WCPC
Size: 7” x 7” x 5”
Weight: 5 lb
Power 12 V, 30 Watts
Features:
internal data logging
one week unattended
up to 10 6 particles/cm 3
in single count mode
Response to Near-Monodisperse Aerosols
1.0
0.8
0.6
0.4
0.2
0.0
Re
spon
se R
ela
tive
to B
utan
ol U
CP
C
4 5 6 7 8 910
2 3 4 5 6 7 8 9100
2
Particle Diameter (nm)
MICRO-ENVIRONMENTAL W ater-CPC DMA-Selected Aerosol, 10/15/0510% mobility window with TSI "long" DMAReference: TSI-3025 Butanol Ultraf ine CPC/ Eff
Freeway-influenced Ambient (Berkeley) Isopropanol Residue
TSI-3781 prototype
ME-WCPC Measurements in a Residential Kitchen
103
104
105
106
Par
ticle
Num
ber
Con
cent
ratin
(#/
cm3)
6:00 PM1/7/2006
7:00 PM 8:00 PM
Residential KitchenButanol CPCs
T3025 T3022
Water CPCs T3786 QME2 QME3 T3785_Calc
Oven on at 6:05 pm
Summary
• 1890’s
Aitken, first explorations of airborne particles nu mber concentration
Identified combustion as source of particles
• 1920s-1950s
Advances on Aitken’s approach: automated instrument s
• 1970’s
First continuous flow condensation particle counter s
widely used, especially as detectors for mobility s ize distributions
• 2003
Introduction of continuous water-based condensation counters
Acknowledgements
• California Air Resources Board, who provided funding for many of the field comparisons.
• ASRC, University at Albany and the EPA SupersitesProgram who made possible the measurements in New York City.
• TSI Inc., who loaned equipment for our field and laboratory testing.
• Quant Technologies LLC, who provided the engineering and detailed instrument design.