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Naama Lang-Yona, Ali Abo Riziq, Yinon Rudich

Department of Environmental Science and Energy Research

Weizmann Institute of Science

Aerosol Complex Refractive Index Aerosol Complex Refractive Index Retrieved by a New Continuous Wave-Cavity Retrieved by a New Continuous Wave-Cavity

Ring Down-Aerosol spectrometerRing Down-Aerosol spectrometer

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From the IPCC report, 2007From the IPCC report, 2007

Large uncertainty!

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AerosolsAerosols

solid particles or liquid droplets that are suspended in a gas

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Characterization of SOA,Characterization of SOA,

from biogenic emission can from biogenic emission can

hence lead to a better hence lead to a better

understanding of these understanding of these

feedbacks feedbacks (Kulmala et. al, 2004). (Kulmala et. al, 2004).

T T STRESSSTRESS? - ? -

VOCVOC ++ OH/O3/NOxOH/O3/NOx SOASOASOASOA

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• Developing a technique, by which we can measure the optical properties of SOA.

• Requirements: Portable system

Highly sensitive

Fast measurements

ObjectivesObjectives

Continues Wave-Cavity Ring Down-Continues Wave-Cavity Ring Down-Aerosol SpectrometerAerosol Spectrometer

(CW-CRD-AS)(CW-CRD-AS)

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Principles of Cavity Ring Down (CRD)Principles of Cavity Ring Down (CRD)

Laser(PMT)

Laser(PMT)

0

1 1*ext

L

Cdα

τ τ⎡ ⎤

= −⎢ ⎥⎣ ⎦

( )( ) 2

extextQ

R N

απ

=

ext scat absα α α= +

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0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

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Extinction efficiency (Q

ex)

Size parameter (x )

Mie fit

( )( ) 2

extextQ

R N

απ

=

n n ik= +%

Absorption Scattering

Mie fit

Complex refractive indexComplex refractive index

Dπχλ

=

Refractive IndexRefractive Index -How much the speed of light (or other waves ) is reduced inside the medium

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CW-CRD setupCW-CRD setup

DMAPurified dry N 2

Monodispersedaerosols

N2 flowN2flow

CPC

Single modeCW Laser

532nm

Optical Isolator AOM

PMT

Piezoring actuator

Iris

event trigger

Telescope

Amplifier

RF generator

computer

D/A card

A/D card

Measured Aerosols

90 x 150cm

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ValidationValidation

The results show that the Mie fit successfully retrieves the refractive index of

different absorbing and scattering aerosols.

PSL

(Polystyrene latex sphere)

Suwannee River Fulvic Acid

Nigrosin

Ammonium Sulphate

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StabilityStability

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(0ττ

α −⋅=CdL

ext

24 DNQ extext ⋅⋅= πα

)1( drC

Lextατ +−=

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AccuracyAccuracyextext Nσα =

σext measuredσext calculated

(3.750.01)×10-9 cm2(3.820.01)×10-9 cm22% Error2% Error

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Characterization of SOA,Characterization of SOA,

from biogenic emission can from biogenic emission can

hence lead to a better hence lead to a better

understanding of these understanding of these

feedbacks feedbacks (Kulmala et. al, 2004). (Kulmala et. al, 2004).

T T STRESSSTRESS? - ? -

VOCVOC ++ OH/O3/NOxOH/O3/NOx SOASOASOASOA

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DMAPurified dry N 2

Monodispersedaerosols

N2 flowN2flow

CPC

CW Laser

532nm

Optical Isolator AOM

PMT

Piezoring actuator

Iris

event trigger

Telescope

Amplifier

RF generator

computer

D/A card

A/D card

SOA to CRDVOC

JPAC chambers in Jülich, GermanyJPAC chambers in Jülich, Germany

Portable Portable

CW-CRD CW-CRD

systemsystem

PlantPlant chamberchamber

ReactionReaction chamberchamber

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Preliminary results, summer 2008Preliminary results, summer 2008

No absorption in the visible wavelength

Emissions from Mediterranean Oak – oxidation with O3/OHIn the JPAC chambers in Jülich, Germany.

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ConclusionsConclusions

• Accuracy –Single mode CW laser single exponential decay

• High repetition rate – Sampling rate of 400Hz (higher repetition rate is achievable).

• Reliability – Good agreement between measured RI for different types of aerosol and previous measurements conducted with Pulsed-CRD and other optical systems. The new system is stable and consistent for long measurement and with varying particle concentrations.

• Suitable for field measurements - High qualities, small dimensions and low power requirements.

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Further Developments Planned in Further Developments Planned in the Futurethe Future

• Addition of UV laser to the current VIS 532nm laser.

• Coupling the system to photo acoustic cell, in order to measure extinction and absorption simultaneously.

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Thank you!!Thank you!!