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Lecture on atmospheric remote sensing [email protected] Long Path (active) DOAS -basic principle -Long path DOAS (UV/vis/IR) -instrumental improvements -Specific applications -white cell -vertical profiles -tomographic inversions

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Lecture on atmospheric remote sensing [email protected]

Long Path (active) DOAS

-basic principle

-Long path DOAS (UV/vis/IR)

-instrumental improvements

-Specific applications

-white cell

-vertical profiles

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

A) Lambert-Beersches Gesetz: ( )I I c l= ⋅ − ⋅ ⋅0 exp σ

DOAS: ’Differentielle Optische AbsorptionsSpektroscopie’

Lecture on atmospheric remote sensing [email protected]

A) Lambert-Beersches Gesetz: ( )I I c l= ⋅ − ⋅ ⋅0 exp σ

DOAS: ’Differentielle Optische AbsorptionsSpektroscopie’

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10Schichtdicke [km]

Rel

ativ

e In

tens

ität

Lichtabschwächung durch Ozon für UV-Licht bei 300nm

σ⋅

⎟⎠⎞⎜

⎝⎛

=l

II

c 0ln

Aus der Intensitätsmessung kann die Konzentration bestimmt werden

Lecture on atmospheric remote sensing [email protected]

SpiegelLichtquelle& Spektrograph

0.5 - 15 km

In der Realität ist es sehr ähnlich....

DOAS: ’Differentielle Optische AbsorptionsSpektroscopie’

A) Lambert-Beersches Gesetz: ( )I I c l= ⋅ − ⋅ ⋅0 exp σ

Lecture on atmospheric remote sensing [email protected]

Long Path DOAS

-basic principle

-Long path DOAS (UV/vis/IR)

-instrumental improvements

-Specific applications

-white cell

-vertical profiles

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

DOAS: ’Differentielle Optische AbsorptionsSpektroscopie’

SpiegelLichtquelle& Spektrograph

0.5 - 15 km

Lecture on atmospheric remote sensing [email protected]

http://http://wwwwww.chem..chem.leedsleeds..acac..ukuk/JMCP//JMCP/imagesimages//doaspicturedoaspicture..jpgjpg

Lecture on atmospheric remote sensing [email protected]

Typisches (früheres) LP-DOAS-Instrument

Spiegel Lichtquelle

Lecture on atmospheric remote sensing [email protected]

Basic requirements for Long path systems

-divergence of the light beam should be small (diameter of a few meters over a distance of several kilometers)

=> Large mirrors

=> Light sources with high luminance (photon flux per area)

αdd

ff

W:W: widthwidth ofof the light beamthe light beam at distance Lat distance L

For W=1m, L=5km:For W=1m, L=5km: sinsinαα = 0.001, = 0.001, αα =0.06°=0.06°

For f = 2m => d =2mm

LW

fd==αsin

For f = 2m => d =2mm

Lecture on atmospheric remote sensing [email protected]

Diplomarbeit Thorsten Hermes, IUP Heidelberg, 1999Diplomarbeit Thorsten Hermes, IUP Heidelberg, 1999

Der Druck der Xenon-Edelgasfüllung steigt während des Betriebs von etwa 8 bar im kalten Zustand auf bis zu 70 bar an.

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Diplomarbeit Thorsten Hermes, IUP Heidelberg, 1999Diplomarbeit Thorsten Hermes, IUP Heidelberg, 1999

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Diplomarbeit Jens Tschritter, IUP Heidelberg, 2007

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

The electromagnetic spectrum

UV/Vis and near IR: Electronic and vibrational transisons (typ. Absorption)

Thermal IR: Vibrational transisons (typ. Emission)

Microwaves: Rotational transisons (typ. Emission)

Lecture on atmospheric remote sensing [email protected]

Example of trace gas cross section:

H2O absorption cross section for 290K

(HITRAN data base)

How can spectra be determined?

(depending on properties of the molecules)

Lecture on atmospheric remote sensing [email protected]

Electronic transitions:

Energy levels:

-exact energy levels can be determined using (time independent) Schrödinger equation,

Example: Hydrogen atom

-energy levels are of the order of electron volts

Example: Hydrogen atom: -Lyman series: ≤ 13.6 eV (≥ 95 nm)

-Balmer series: ≤ 3.4 eV (≥ 430nm)

-Paschen series: ≤ 1.5 eV (≥ 1282nm)

Lecture on atmospheric remote sensing [email protected]

Different kinds of molecular vibrationsExampleExample: CO: CO22 ((DegreeDegree ofof freedom for vibrationfreedom for vibration: 4): 4)

SymmetricSymmetric vibrationvibration Assymmetric vibrationAssymmetric vibration

Deforming vibrationDeforming vibration

Lecture on atmospheric remote sensing [email protected]

Energy levels for different statesof vibration

TheThe distancedistance between the between the energy levels is constantenergy levels is constant::

ω

Lecture on atmospheric remote sensing [email protected]

Energy levels for different statesof vibration

TheThe distancedistance between the energy between the energy levels are not constantlevels are not constant. For. Forincreasingincreasing vv thethe distancedistance decreasesdecreases..There exist onlyThere exist only aa limited numberlimited numberofof eneryg levelseneryg levels..

2

0 01 1( )2 2

⎛ ⎞ ⎛ ⎞= + − +⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

eG v v v xν ν

Lecture on atmospheric remote sensing [email protected]

Absorption cross section of the OClO molecule

0

2E-18

4E-18

6E-18

8E-18

1E-17

1.2E-17

1.4E-17

300 320 340 360 380 400 420 440Wavelength [nm]

Abs

orpt

ion

cros

s se

ctio

n [c

m²]

Lecture on atmospheric remote sensing [email protected]

250 300 350 400 450 600 650 7000

100200

Detection Limit

200 pptL=1km

1 pptL=16km

2 pptL=12km

20 pptL=12km

500 pptL=5km

5 pptL=5km

100 pptL=5km

200 pptL=5km

1 ppbL=5km

Phenol

Wavelength [nm]

04080

20 pptL=1km

50 pptL=1km

250 pptL=1km

para-Kresol

05

10

Toluol

01020

Benzol

0100200

IO

050 BrO

020 ClO

01

HCHO

0100 NO3

04

HONO

0

2NO2

048

SO2

0

4250 300 350 400 450 600 650

50 pptL=5km

σ'[1

0-19 c

m2 ]

O3

Solution:

-identification of different absorption processes by their spectral signature

=> Differential optical absorption spectroscopy (DOAS)

-consideration of scattering processes by broad band spectral structures, e.g. loworder polynomials

Lecture on atmospheric remote sensing [email protected]

glass fibre

Spectrograph +30°C

Grating

Detector-35°C

Typical DOAS-Spectrograph

Light

Lecture on atmospheric remote sensing [email protected]

Schematic of a Czerny-Turner monochromator

Lecture on atmospheric remote sensing [email protected]

glass fibre

Spectrograph +30°C

Grating

Detector-35°C

Typical DOAS-Spectrograph

Light

channel 1channel 2

electronicbox

gratings

Sun diffuser

channel 4channel 3

beamsplitter

gratings

pre-disperserprism sun

channelseparator

Scannigmirror

nadir

telescopemirrors

595- 405- 240- 311-793 nm 611 nm 316 nm 405 nm

lampcalibrationunit

Lecture on atmospheric remote sensing [email protected]

Absorption spectroscopy

⎭⎬⎫

⎩⎨⎧

⋅⎟⎠

⎞⎜⎝

⎛+−⋅= ∫ ∑

l

si

ii dssII0

0 )()()(exp)()( λερλσλλ

Beer- Lambert-law :

σi: Absorption cross section of trace gas iρi: Concentration of trace gas iεs: Scatter coefficient

=> From the knowledge of the absorption cross section it is possible to determine the trace gas concentration

Optical depthOptical depth ττ

Lecture on atmospheric remote sensing [email protected]

Example: NO2 observation

0.E+00

2.E-19

4.E-19

6.E-19

8.E-19

250 300 350 400 450 500 550 600 650 700 750

Wavelength [nm]

abso

rptio

n cr

oss

sect

ion

[cm

²]

Typical wavelength window

l⋅⋅= ρστPath length: 6km

NO2 mixing ratio: 10ppb (parts per billion)

Air concentration: 2.9e19 molec/cm³

NO2 concentration: 2.9e11 molec/cm²

τ ≈ 0.07

=> I/I0 ≈ 0.93

Lecture on atmospheric remote sensing [email protected]

-also scattering reduces the measured intensity

Lecture on atmospheric remote sensing [email protected]

460 480 500 520 540

Wellenlänge [nm]

Inte

nsit

t I(

)

O3-Absorption

NO2-Absorption

Meßspektrum

'differentielle'optische Dichte

''ln0

σ⋅

⎟⎠⎞⎜

⎝⎛

=l

II

c

I’0

I

σ3

σ1

σ2

λ3λ2λ1

σdiff

Wavelength [arb. Units]

Cro

ss s

ectio

n [a

rb. U

nits

]

Lecture on atmospheric remote sensing [email protected]

Platt et al., Platt et al., 19801980

Lecture on atmospheric remote sensing [email protected]

Platt et al., Platt et al., 19801980

Lecture on atmospheric remote sensing [email protected]

0.96

0.99

1.02

400 300 200 100

pixel

atm

os. s

pekt

.

305 310 315

0.9998

1.0000

1.0002

resid

ual

wavelength [nm]

0.998

1.000

1.002

HCH

O

0.996

0.999

1.002

SO2

0.998

1.000

1.002

NO

2

0.998

1.000

1.002

O3

Example of a spectral analysis of O3, NO2, SO2, and HCHO in the polluted air of Heidelberg. The absorptions identified in the atmospheric spectrum (top trace) were: O3: 21.1 ± 0.5 ppb, SO2:0.64 ±0.01 ppb, and HCHO: 3.7 ± 0.1 ppb. The NO2 mixing ratio was not determined since this wavelength interval is not optimal for its analysis. The missing area around 312 nm was excluded from the analysis procedure.

Lecture on atmospheric remote sensing [email protected]

425 430 435 440

0.996

0.998

1.000

1.002

wavelength [nm]

residual

0.996

0.998

1.000

1.002

optic

al d

ensi

ty atmospheric spectrum

0.99995

1.00000

1.00005IO reference

Comparison of atmospheric spectrum after the removal of NO2 and H2O absorptions. The comparison with the IO absorption cross section clearly shows the presence of IO [Alicke et al, 1999].

Lecture on atmospheric remote sensing [email protected]

NO3 time series collected in the marine boundary layer of Mace Head, Ireland. The letters denote the origin of the observed air masses: A, Atlantic, P polar marine, EC, easterly continental, NC, northerly continental

[Allan et al, 2000].

Lecture on atmospheric remote sensing [email protected]

Catalytic ozone destruction mechanisms:

X + O3 → XO + O2

XO + O → X + O2

Net: O + O3 → 2O2

with:

X = OH, NO, Cl, Br

Lecture on atmospheric remote sensing [email protected]

Observation of Observation of volcanic emissionsvolcanic emissions

C. Kern, IUP HeidelbergC. Kern, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Halogen compounds in coastal regions?

C. Peters, PhD-thesis, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

K. Hebestreit,K. Hebestreit,

PhDPhD--thesisthesis, IUP , IUP HeidelbergHeidelberg

Lecture on atmospheric remote sensing [email protected]

High High BrO coincides with low BrO coincides with low O3O3

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Long Path DOAS

-basic principle

-Long path DOAS (UV/vis/IR)

-instrumental improvements

-Specific applications

-white cell

-vertical profiles

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

Retro Reflector

Plane Mirror

Compensation of turbulent beam dispersion by a (corner-cube) retroreflector arrangement (upper panel) in comparison to reflection by a plane mirror (lower panel).

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

J. Stutz, J. Stutz, PhDPhD--thesisthesis, IUP Heidelberg, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

J. Stutz, J. Stutz, PhDPhD--thesisthesis, IUP Heidelberg, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

R. Ackermann, R. Ackermann, PhDPhD--thesisthesis, IUP Heidelberg, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

J. J. TschritterTschritter, , DiplomaDiploma--thesisthesis, IUP Heidelberg, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

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Schematic set-up of a DOAS system using a coaxial arrangement of transmitting- and receiving telescope in conjunction with a retro-reflector array [Geyer et al. 2001]. This type of set-up pioneered by Axelsson et al. [1990] has become the standard for artificial - light DOAS systems for research in the recent years.

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

C. Hak, Dissertation, IUP Heidelberg, 2007C. Hak, Dissertation, IUP Heidelberg, 2007

Lecture on atmospheric remote sensing [email protected]

J. J. TschritterTschritter, , DiplomaDiploma--thesisthesis, IUP Heidelberg, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

DOAS instrument used during theSOS field campaign in Nashville, TN, 1999, picture : Cathy Burgdorf, http://www.atmos.ucla.edu/~jochen/research/doas/DOAS.html

Lecture on atmospheric remote sensing [email protected]

Long Path DOAS

-basic principle

-Long path DOAS (UV/vis/IR)

-instrumental improvements

-Specific applications

-white cell

-vertical profiles

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

-Multi-Reflektions-System (White-Zelle):

Hohlspiegel

0.1 - 15 m

Lichtquelle& Spektrograph

Lecture on atmospheric remote sensing [email protected]

A. Geyer

Schematic optical set-up of the 'White' multi-pass system with a base path of 15 m as used during a field campaign in Pabstthum/Germany.

500 W Xe -arclamphouse

Quartz fibre withmode-mixer

Transferoptics

PC

Lecture on atmospheric remote sensing [email protected]

Schematic of the DOAS setup in the EUPHORE chamber in Valencia, Spain [Volkamer et al. 2002].

Lecture on atmospheric remote sensing [email protected]

Long Path DOAS

-basic principle

-Long path DOAS (UV/vis/IR)

-instrumental improvements

-Specific applications

-white cell

-vertical profiles

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

B. Alicke

DOAS

4 m

1.25 km

1.57 m

2.45 m

1.8 m

Sonic Anemometer

2.1m

Set-up of the experiment to measure gradients and fluxes of NO2 and HONO during the PIPAPO experiment. The DOAS instrument aimed sequentially at the three retroreflectors mounted on the tower at 1.25 km distance.

Lecture on atmospheric remote sensing [email protected]

020406080

5/29/1998 12:00 5/30/1998 00:00 5/30/1998 12:00

0.0

0.2

0.4

-4

-2

0

0.0

0.2

0.4

0.6

0

5

10

5/29/1998 12:00 5/30/1998 00:00 5/30/1998 12:00

-5x1011

05x1011

-0.5

0.0

0.5

a

[NO

2] (p

pb) upper LP

middle LP lower LP

d u*

u * (m

s-1) z/L

z/L

measured calculated

e

K (m

2 s-1)

b

G

radi

ent

(ppb

m-1)

f

NO2 flux

NO

2 flu

x [m

olec

/cm

2 s]

vdep

vde

p (cm

s-1)

0

2

4

6 c

win

d sp

eed

(m

s-1)

090180270360

win

d di

r

B. Alicke

NO2 gradients during the night of May 29, 1998 in Milan, Italy. Gradients well above the detection limit were observed continuously for many hours during this night.

Lecture on atmospheric remote sensing [email protected]

0

1

2

35/29/1998 12:00 5/30/1998 00:00 5/30/1998 12:00

01002003004000.0

0.4

0.8

5/29/1998 12:00 5/30/1998 00:00 5/30/1998 12:00

-2x1010

0

2x1010

-0.5

0.0

0.5

0.00

0.03

0.06

-1

0

1

a

HO

NO

(ppb

) upper LP middle LP lower LP

c

NO

(p

pb)

b

gra

dien

t(p

pb m

-1)

e

HONO flux

HO

NO

flux

(m

olec

cm

-2 s

-1)

net vdep

vde

p (cm

s-1)f

d

[HO

NO

][N

O2]

HO

NO

corr

(ppb

)

B. Alicke

HONO gradients during the night of May 29. (a) shows the mixing ratios on the individual light paths (LP). The gradient is displayed in (b). To remove the influence of direct HONO emissions we calculated HONOcorr by subtracting 0.65% of the NOx(not shown here) from the HONO mixing ratios (d). The ratio of HONO to NO2 mixing ratios is displayed in (e). The fluxes and net deposition velocities is shown in (f)..

Lecture on atmospheric remote sensing [email protected]

J. Stutz

RTU 115mRTM 99mRTL 70m

DOAS Systems

WT 44mME 2m

6.1 km1.9 km750m

Setup during the TEXAQS 2000 experiment. Five retroreflector arrays were mounted at different distances and altitudes. The measurements weree performed by two DOAS instruments [Stutz et al, 2004].

Lecture on atmospheric remote sensing [email protected]

0 5 10 150

20406080

100120

altit

ude (

m)

0 5 10 15

2254

0 5 10 15

0042

0 5 10 15

0240

NO2 (ppb)

0 50 1000

20406080

100120

0 50 100 0 50 100 0 50 100

NO3 (ppt)

0 20 40 600

20406080

100120

0 20 40 60 0 20 40 60 0 20 40 60

O3 (ppb)

120

2032

J. Stutz

Vertical mixing ratio profiles during the night of 8/31 – 9/1 at four different times (noted on top of the graphs). The N2O5 mixing ratios shown are calculated from the steady state of measured NO2 ,NO3 , and N2O5 [Stutz et al., 2004].

Lecture on atmospheric remote sensing [email protected]

H.-J. Veitel, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

H.-J. Veitel, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

H.-J. Veitel, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

H.-J. Veitel, IUP Heidelberg

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Long Path DOAS

-basic principle

-Long path DOAS (UV/vis/IR)

-instrumental improvements

-Specific applications

-white cell

-vertical profiles

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

A. A. HartlHartl, Dissertation, IUP Heidelberg, 2007, Dissertation, IUP Heidelberg, 2007

Lecture on atmospheric remote sensing [email protected]

tomographic measurement setup during the BAB II campaign at the motorway BAB 656 between Heidelberg and Mannheim

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Modelled concentration distribution of NO2 and measurement setup

Measured (reconstructed) concentration distribution of NO2

Lecture on atmospheric remote sensing [email protected]

KaiKai--Uwe Mettendorf, Dissertation, IUP Heidelberg, 2006Uwe Mettendorf, Dissertation, IUP Heidelberg, 2006

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Measurement setup for the validation measurements

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Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]

Summary (I) Long Path (active) DOAS

-most direct application of the Lambert-Beer law

-long absorption path is needed to become sensitive even for small trace gas concentrations

-many trace gases were first observed by LP DOAS

-measurements also during night

-only the averaged trace gas concentration along the light path can be obtained (from simple LP DOAS)

-expensive and complicated instrumental set-up

Lecture on atmospheric remote sensing [email protected]

Summary (II) Long Path (active) DOAS

-recently many instrumental improvements were introduced, e.g. fibre optics, LED as light sources, which make instruments much cheaper and easier to operate

-many specialisations of LP-DOAS exist for specific applications:

-White (multi-reflection) system

-light paths at different altitudes

-balloon-borne reflectors

-tomographic inversions

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]://www.lumileds.com/pdfs/techpaperspres/SID-BA-Paolini.PDF

Leuchtdichte von LEDs

Zum Vergleich:

Sonnenoberfläche1,5 x 10

9cd/m

2

Xenon Hochdrucklampetyp 4x 10

8cd/m

2

Glühdraht einer Glühlampe5 bis 35x 10

6cd/m

2

moderne Leuchtstofflampe0,3 bis 1,5x 10

4cd/m

2

Nachthimmeletwa 10

-11cd/m

2

Lecture on atmospheric remote sensing [email protected]

Lichtausbeute (Effizienz)Die Lichtausbeute ist ein Maß für die effektive Umwandlung elektrischer Energie in Lichtenergie. Die Effizienz der LED liegt zur Zeit bei bis zu 55 lm/W.

Lecture on atmospheric remote sensing [email protected]

Lecture on atmospheric remote sensing [email protected]