1

Recent CAVIAR activities at Cambridge

A.J.L. Shillings1, S.M. Ball2 and R.L. Jones1

1University of Cambridge, Department of Chemistry, Lensfield Road, Cambridge, CB1 2EW2 University of Leicester, Department of Chemistry, Leicester, LE1 7RH

2

Outline

1. BBCRDS Instrumental modifications• Previous iteration of design gave access to v.high temperatures (150C), but

introduced T gradients and uncertainties.

2. BBCRDS Measurements and Analysis• Results using different datasets to fit the measured data

3. Infra-Red BBCEAS introduction• New system hardware

• Potential light sources

• Complexities of CEAS vs CRDS.

3

Absorption cell modifications

•‘Coolant’ = water/antifreeze mix

•Tested T range 5 – 95 C (expect larger)

•V. Small (<1C) T gradients at 90C

•Entire gas delivery system

thermostatted at cell temperature –

No cold points (avoids aerosol)

4

Fitting Results (1)

0.0E+00

5.0E-09

1.0E-08

1.5E-08

2.0E-08

2.5E-08

3.0E-08

3.5E-08

4.0E-08

4.5E-08

5.0E-08

606 608 610 612 614 616 618 620 622

Wavelength / nm

Ab

so

rba

nc

e /

cm

-1

Measured

Predicted Dimer

•44% RH at 88 C (361K) – 6.1*1018 molec cm-3

•‘Average’ K(361) = 0.16 atm-1 (6.4*10-22 molec-

1 cm3)

5

Water Results (1)

0.0E+00

5.0E-09

1.0E-08

1.5E-08

2.0E-08

2.5E-08

3.0E-08

3.5E-08

4.0E-08

4.5E-08

5.0E-08

606 608 610 612 614 616 618 620 622

Wavelength / nm

Ab

so

rba

nc

e /

cm

-1

Measured

HITRAN '06

HITRAN’06 -clearly has imperfections.

6

Water Results (1)

0.0E+00

5.0E-09

1.0E-08

1.5E-08

2.0E-08

2.5E-08

3.0E-08

3.5E-08

4.0E-08

4.5E-08

5.0E-08

606 608 610 612 614 616 618 620 622

Wavelength / nm

Ab

so

rba

nc

e /

cm

-1

Measured

UCL '08

UCL ’08 - seems to be doing a much better job.

- self and foreign broadening parameters taken from HITRAN

(either default values [Foreign 0.07cm-1atm-1, Self 0.12cm-1atm-1], or average (assigned) values over wavelength range of interest)

7

Water Results (2)

0.00E+00

2.00E-27

4.00E-27

6.00E-27

8.00E-27

1.00E-26

1.20E-26

1.40E-26

551 553 555 557 559 561 563 565 567

Wavelength / nm

Ab

sorp

tio

n C

ross

Sec

tio

n /

cm2/m

ole

cule

UCL_08

HITRAN 06

•UCL 08 data greatly improved fits and residuals in green region (Fieldwork - NO2 and I2 retrievals) compared to HITRAN 06

8

Water Results (3)

-2.00E-07

-1.00E-07

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

600 602 604 606 608 610 612 614

Wavelength / nm

Abs

orpt

ion

Coe

ffic

ient

/ c

m-1

MeasuredFitted (HITRAN)Residual

[H2O] series at 95C

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Water Results (3)

-2.00E-07

-1.00E-07

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

600 602 604 606 608 610 612 614

Wavelength / nm

Abs

orpt

ion

Coe

ffic

ient

/ c

m-1

MeasuredFitted (HITRAN)Residual

-3.00E-08

-1.00E-08

1.00E-08

3.00E-08

5.00E-08

7.00E-08

600 602 604 606 608 610 612 614

Wavelength / nm

Ab

sorp

tion

Co

eff

icie

nt

/ cm

-1

Residual

Lorentzian Fit

0.0E+00

1.0E-07

2.0E-07

3.0E-07

4.0E-07

5.0E-07

6.0E-07

0.E+00 2.E+18 4.E+18 6.E+18 8.E+18

[Water] / molecules/cm3L

ore

ntz

Sca

lin

g F

acto

r

10

Water Results (3)

-2.00E-07

-1.00E-07

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

600 602 604 606 608 610 612 614

Wavelength / nm

Ab

so

rpti

on

Co

eff

icie

nt

/ c

m-1

MeasuredFitted (UCL)Residual

11

Water Dimer Results (3)

-2.00E-07

-1.00E-07

0.00E+00

1.00E-07

2.00E-07

3.00E-07

4.00E-07

5.00E-07

600 602 604 606 608 610 612 614

Wavelength / nm

Ab

so

rpti

on

Co

eff

icie

nt

/ c

m-1

MeasuredFitted (UCL)Residual

-5.00E-08

-3.00E-08

-1.00E-08

1.00E-08

3.00E-08

5.00E-08

7.00E-08

9.00E-08

1.10E-07

1.30E-07

600 602 604 606 608 610 612 614

Wavelength / nm

Ab

so

rpti

on

Co

eff

icie

nt

/ c

m-1

Residual

y = 0.9898x

0.00E+00

1.00E+18

2.00E+18

3.00E+18

4.00E+18

5.00E+18

6.00E+18

7.00E+18

0.00E+00 1.00E+18 2.00E+18 3.00E+18 4.00E+18 5.00E+18 6.00E+18 7.00E+18

BBCRDS [H2O] / moleclues /cm3

Hy

gro

m. [

H2O

]/ m

ole

clu

es

/cm

3

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Spectral Coverage

550 – 2500nm water bands

BBCRDS

950nm 550nm

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Spectral Coverage

550 – 2500nm water bands

2250nm ~950nmIR-BBCEAS

BBCRDS

950nm 550nm

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IR BBCEAS

•Hardware

•Princeton Instruments Spectra-Pro SP-2300i spectrograph

•Princeton Instruments OMA-V InGaAs linear photodiode array (1024 pixels). Spectral coverage 2.2 – ~1.0 μm. (Liquid nitrogen cooled).

•In situ - currently writing control and acquisition software.

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IR BBCEAS

Light Sources

•Supercontinuum fibre-optic laser (Fianium SC400)

•High Power, excellent coherence (good for coupling light into a cavity), but long term stability (intensity and spectral) to be quantified

•High Power LED

•Group has extensive experience with LEDs, can be driven at high frequency (phase-shifting potential), cheap but relatively low power (S/N issues?)

•Xenon arc lamps

•High power but potential instability.

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IR BBCEAS

CEAS not inherently calibrated (unlike CRDS) – need a method to determine mirror reflectivity

Possibilities:

•Phase shifting

•Introduce known absorber

•e.g. (O2)2

•calibrated cylinder of an organic?

d

R

I

Io )(1.1(

)(

1

)(

11(

occ.f.

tan

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Conclusions

•Fitting challenging owing to uncertainties in databases.

•UCL dataset seems to be doing a better job than HITRAN.

•Attempt to develop fitting methods that don’t rely on databases. (fitting low [H2O] to high [H2O])

•Complete setup of IR system

•Trial light sources

•Determine most suitable method to derive R(λ)

Next Steps