1 Naama Lang-Yona, Ali Abo Riziq, Yinon Rudich Department of Environmental Science and Energy...

1

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

2

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

Large uncertainty!

3

AerosolsAerosols

solid particles or liquid droplets that are suspended in a gas

4

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

5

• 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)

66

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= +

7

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

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

8

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

9

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

10

StabilityStability

)11

(0ττ

α −⋅=CdL

ext

24 DNQ extext ⋅⋅= πα

)1( drC

Lextατ +−=

11

AccuracyAccuracyextext Nσα =

σext measuredσext calculated

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

12

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

13

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

14

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.

15

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.

16

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.

17

Thank you!!Thank you!!