Instrumentation for Ambient UltrafineParticle Measurement

historic perspectivesand

recent developments----

Susanne HeringAerosol Dynamics Inc.

80x103

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6040200Total Particle Number Concentration (10 - 360 nm)

Fresno First StreetDecember 2000 - Feburary 2001R = 0.97slope = 0.71 ± 0.003 intercept = 1120 ± 90

14x103

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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

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Non-Dimensional Axial Position (x/UR2)

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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

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Particle Diameter (nm)

Ambient Aerosol (Berkeley, CA) Vehicle Tunnel Aerosol (Caldecott)

TSI-3785

0.0

0.2

0.4

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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

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PC

-410

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x (%

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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

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Diameter (nm)

Run 742/3/2004 18:15

WCPC-0.2sec WCPC-10sec TSI3025-0.2sec TSI3025-10sec

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Run 742/3/2004 18:15

WCPC-2sec WCPC-20sec TSI3025-2sec TSI3025-20sec

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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

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(#/c

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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

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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

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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

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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.