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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
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
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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
)11
(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!!