Part 3 – Discussion of optical spectroscopic measurement techniquesmeasurement techniques

Nov 4 DOASNov 5 CRDSNov 11 IBB‐CEASNov 13 LIFNov 18 FTIRNov 20 RAMAN

Nov 4 2008

CHEM 5161CHEM 5161

Presentation topics

• Sum Frequency Generation Spectroscopy/ (*) Sum Frequency Vibrational Spectroscopy                        http://dx doi org/10 1021/jp065277lhttp://dx.doi.org/10.1021/jp065277l

• CASR – Coherent Anti‐Stokes Raman Scatt. Spectroscopy * http://dx doi org/10 1021/jp035693vhttp://dx.doi.org/10.1021/jp035693v

• SERS – Surface enhanced Raman Spectroscopy (*) http://dx doi org/10 1021/jp0257449http://dx.doi.org/10.1021/jp0257449

• Developments in Microscopy htt //d d i /10 1021/ 0606756http://dx.doi.org/10.1021/ac0606756

• ATR‐IR – Attenuated Total Reflection IR (*)

• Chemiluminescence

Presentation topics (cont)

• LIDAR – Light detection and Ranging *

• Photoacoustic Spectroscopy (*)Arnott WP et al. (1999) Atmos. Environ. 33, 2845‐2852

• CRD – Cavity Ringdown Spectroscopy *                                   http://dx.doi.org/10.1139/P05‐054

• I‐DOAS – Imaging Differential Optical Absorption Spectroscopy *http://dx.doi.org/10.1016/j.jvolgeores.2005.05.004

i l l l l• Single Molecule Fluorescence Spectroscopyhttp://dx.doi.org/10.1063/1.1589587

* indicates that the technique is discussed in Hollas or at textbook level*  indicates that the technique is discussed in Hollas or at textbook level(*) indicates that the technique is referred to in Hollas

Your presentation should include• Review of the technique

– Theory background Wh t tit i t ll b i d ?– What quantity is actually being measured ?

– What are known strength and what are inherent weaknesses of this specific technique?

• Experimental Setup– Light sources, dispersive elements (if any), detectors, are there other key 

components ?– Arrangement of the components in the measurement setup– If this specific arrangement/application allows to overcome what is typicallyIf this specific arrangement/application allows to overcome what is typically 

known to be a weakness with similar techniques, you should elaborate on this fact

• Measurements• Discussion (may include one or two sample applications)• Discussion (may include one or two sample applications)

– What is demonstrated in this paper– What remains as open question

• Outlook– What is the potential of this technique– Where is this technique going ?

Your paper should includeYour paper should include

• What hardware components are being used?What hardware components are being used?

• What is the intellectual merit of the approach?

• Briefly discuss one or two example applicationsBriefly discuss one or two example applications

• http://portal.isiknowledge.com/portal.cgi?DestApp=WOS&Func=FrameFunc Frame

Differential Optical Absorption Spectroscopy (DOAS)

Lambert-Beer‘s LawIn Theory: Abs Cross SectionIn Theory:

I(λ) = I0(λ)•e‐ σ (λ)⋅c⋅L

I R lit R l i h tt i λ 4 Mi S tt i λ (1 3)

Abs. Cross Section

In Reality:

I(λ) = I0(λ)•e‐ [Σσi (λ)⋅ci⋅L + ( εRay(λ) + εMie(λ)) ⋅L] ⋅ T(λ))

Rayleigh scattering ~ λ‐4 Mie Scattering~ λ-(1…3)

The DOAS Approach:

I(λ) = I (λ)•e‐ [Σσ‘i (λ)⋅ci⋅L + (σbi⋅ci + εRay(λ) + εMie(λ)) ⋅L] ⋅ T(λ))I(λ) = I0(λ)•e [ i ( ) i ( bi i  Ray( ) Mie( )) ] ⋅ T(λ))

narrow- wide band extinction

Remove by high-pass filtering

Differential Optical Absorption Spectroscopy –

The Idea

I'Ia

• Use differences ofintensities atdifferent wavelengths

D'

I 0I0

nten

sitä

tIn

tens

ity

g

• Record the intensityin many(typ several 100)

b

II (typ. several 100)wavelength channels(entire spectra)

�'

b

)[c

m2 ] • High pass-filtering

of spectra⇒ remove continuum

�b

�(�

) ⇒ remove continuum

• Fit reference spectra⇒ Make use of all

� [nm]spectral information

Measured- and High-Pass Filtered SO2 Spectrum1.5

SO Cross-Section (σ(λ)1.0

0.0

0.5

1.0

SO2 Cross Section (σ(λ)(0.01 nm resolution) σx

σ [1

0-18 c

m2 ]

0.7

0.8

0.9 measured spectrumPolynom 5th order

units

]

Measured SO2absorption spectum(0 2nm resolution)

I

I0

I [re

lativ

e un

its]

0.0

0 4

0.5

0.6

I [re

lativ

e

High pass filteredabsorption spectrum

(0.2nm resolution)

0.050.3

0.4

290 300 310

p p(polynom 5th degree)

Wavelength [nm]0.00

elat

ive

units

]

-0.05

high pass filtered atmospheric spectrum

log

(I) [r

e

295 300 305 310

fitted SO2 cross section spectrum

Wavelength [nm]

Differential Cross Sections ofSections of

Atmospheric MoleculesMolecules

Active DOAS: use artifical light source (e g Xe-arc lamp)(e.g. Xe arc lamp)

- -1. Long Path DOAS (LP DOAS)II

c =0ln

I0 IDet.

Lc

⋅=σL = 0.2 … 15 km

2. Folded-Path DOAS

L = 0.1 … 40 m

Det

EUPHORE, SAPHIR

Det.

Passive DOAS: use natural light source (e.g. sun, moon, stars ...)( g , , )

3. Zenith Scattered Light (ZSL-DOAS)30 cm

Det.

4. Multi Axis DOAS (MAX-DOAS)

Det.

Derives information about the altitude distribution of a trace gas or aerosol layer.

Multi‐Axis DOAS the Idea

ϑ

z

c(z)

trace gas profile

Sun

Va ⋅− )1( S h idzds

scattering

Va ⋅− )1( Stratospheric Trace Gas Layer

Tropopausescattering process

p p

α

Va ⋅

Tropospheric Trace Gas Layer

( ) ⎟⎞

⎜⎛ +=+=

11111 aaVSSSTotal Slant Column: ( ) ⎟

⎠⎜⎝

−+⋅=+=ϑαϑα cos

1sincossin

aaVSSS StratTropColumn:

Airborne Imaging DOAS

ve g

roun

d

nn-1

n-2n-3

Altit

ude

abov

1 scan/second

Swath width50 pixel

Airborne Imaging DOAS:• Create 2-D trace-gas maps with high

ti l l ti (10 100 2)spatial resolution (10x100 m2)• Bridge spatial scales between local air quality monitoring networks and satellites

Lohberger et al. 2004, Applied Optics, 43 (24) 4711Bobrovski et al. 2006, Journal of Volcanology and Geothermal Research 150 (4) 329

(cont.) Satellite – Borne DOAS5. Nadir Geometry

GOME, GOME 2ILASSCIAMACHYOMI, ILAS-2 ...

6. Limb Geometry

e.g. SCIAMACHY

7. Occultation

e.g. SCIAMACHY

North-America 1996-2001

Resolution: 80 x 40 km, Cities over 200.000 inhabitants are encircled, Beirle et al. 2004

1015 molec. cm-2