1 Recent CAVIAR activities at Cambridge A.J.L. Shillings 1, S.M. Ball 2 and R.L. Jones 1 1 University of Cambridge, Department of Chemistry, Lensfield Road, Cambridge, CB1 2EW 2 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) 44% RH at 88 C (361K) – 6.1*10 18 molec cm -3 ‘Average’ K (361) = 0.16 atm -1 (6.4* molec -1 cm 3 )

5 Water Results (1) HITRAN’06 -clearly has imperfections.

6 Water Results (1) UCL ’08 - seems to be doing a much better job. - self and foreign broadening parameters taken from HITRAN (either default values [Foreign 0.07cm -1 atm -1, Self 0.12cm -1 atm -1 ], or average (assigned) values over wavelength range of interest)

7 Water Results (2) UCL 08 data greatly improved fits and residuals in green region (Fieldwork - NO 2 and I 2 retrievals) compared to HITRAN 06

8 Water Results (3) [H2O] series at 95C

9 Water Results (3)

10 Water Results (3)

11 Water Dimer Results (3)

12 Spectral Coverage 550 – 2500nm water bands BBCRDS 950nm550nm

13 Spectral Coverage 550 – 2500nm water bands 2250nm~950nm IR-BBCEAS BBCRDS 950nm550nm

14 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.

15 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.

16 IR BBCEAS CEAS not inherently calibrated (unlike CRDS) – need a method to determine mirror reflectivity Possibilities: Phase shifting Introduce known absorber e.g. (O 2 ) 2 calibrated cylinder of an organic? c.f.

17 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 [H 2 O] to high [H 2 O]) Complete setup of IR system Trial light sources Determine most suitable method to derive R(λ) Next Steps