Laser spectroscopic study of ozone in the 100←000 band for the SWIFT instrument M. Guinet, C. Janssen, D. Mondelain, C. Camy-Peyret LPMAA, CNRS- UPMC (France) 18/06/2010

Importance of ozone in terrestrial atmosphere In the stratosphere: UV filter for solar radiation Key role in tropospheric chemistry (OH radical precursor) Green house gas  Studied by a large palette of instruments (UV spectrophotometer, Dobson spectrometer, FTIR…)  1% uncertainty for intensity is required for atmospheric applications (reactive gas!)  Comparison of published data sets → several % inconsistencies for intensities (10 µm bands)

- O 3 : tracer for atmospheric winds (SWIFT instrument) - Stratospheric wind speed (Doppler shift) & ozone concentration measurements - Understand the transport of O 3 in the stratosphere High accuracies required (for the 15 strong 16 O 3 transitions) - Absolute positions:  5  cm -1 (   13 m s -1 ) - Absolute intensities:  1% Other spectroscopic parameters measured:  air,  air,  self SWI Stratospheric Wind Interferometer FT For Transport studies (SWIFT)

A set up at the border of metrology and spectroscopy Laser Diode  / < µm Stabilization principle Stabilized HeNe  / = nm Michelson interferometer

A set up at the border of metrology and spectroscopy Laser Diode  / < Stabilized HeNe  / = Michelson interferometer Stabilization principle Stabilized HeNe  / = nm Laser Diode  / < µm

A set up at the border of metrology and spectroscopy Laser Diode  / < Stabilized HeNe  / = Michelson interferometer Stabilization principle Stabilized HeNe  / = nm Laser Diode  / < µm

A set up at the border of metrology and spectroscopy Laser Diode  / < Stabilized HeNe  / = Michelson interferometer Stabilization principle Stabilized HeNe  / = nm Laser Diode  / < µm

A set up at the border of metrology and spectroscopy Laser Diode  / < Amplitude modulation scheme good S/N (several thousand) Both highly tunable and stabilized system Ultra flexible setup (atmospheric windows accessible) Stabilized HeNe  / = Michelson interferometer Stabilization principle Stabilized HeNe  / = nm Laser Diode  / < µm

Stabilized spectrometer Laser Diode O 3 Generation UV O3O3 N2ON2O (FP)D D C D PT 100 D Laser Diode UV O 3 Generation system Step by step mode Step < cm -1 S/N : 3000 I0I0 FP N2ON2O Accuracy (2  ): Position < cm -1 Intensity < 2% M. Guinet, D. Mondelain, C. Janssen, C. Camy- Peyret, JQSRT, 111, (2010) Interferometer locked onto stabilized HeNe laser

Spectra Linearization Absolute calibration SWIFT Line points

Metrological approach Reduction and taking into account of systematic biases : Sample purity, spectrometer, experimental conditions… Traceability : Following the BIPM recommendation (photometer UV). Calibrated tools (PT 100, micrometer, pressure gauge, stabilized HeNe). Expertise : O 3 sample purity test (> 99.5 % purity sample) : IR spectrometer (CO 2, H 2 O, N 2 O) mass spectrometer (N 2, NO x ) pressure (O 2, N 2, non condensable gases), Stable conditions (temperature, very low ozone decomposition 2- 4 ‰ / hour) Checking : Check BIPM UV recommended cross section (Hearn) with a calibrated pressure gauge. C. Janssen and M. Guinet, RSI., submitted     Hearn A. G., Proc. Phys. Soc., 78 (1961) Mass spectrometer

High accuracy absorption measurement of O 3 cross section at nm International standard (BIPM) : our measures : M. Guinet, C. Camy-Peyret, D. Mondelain and C. Janssen, Refinement of the ozone standard – absolute ozone absorption cross section at the mercury emission line position nm, Metrol., en préparation  =  cm² (± 2.1%)  =  cm² (± 0.7%)

Estimated uncertainties between 0.8 and 1.3% considering: –statistical error over the 11 spectra with pure O 3 –systematic errors (T, offset,  UV, L UV, L IR …) Results on intensities Comparison with HITRAN08: -2.2  1.1(2  ) % (Our UV cross section) -2.6  1.3(2  ) (Mauersberger cross section)

Cross cell : UV and IR measured simultaneously 3.6% inconsistencies between UV (Hearn) and IR (HITRAN 08) recommended values in agreement with Picquet-Varrault Results on intensities Picquet-Varrault et al, J. Phys. Chem A, 109 (2005) UV IR

Absolute positions of strong O 3 lines The N 2 O line positions were accurately measured by an heterodyne experiment (Maki and Wells) Linearization and calibration procedure applied to O 3 and N 2 O spectra N 2 O positions → overall accuracy of 8  cm -1 (2  )  Wind speed uncertainty: ~ 20 m s -1 O 3 positions → Mean difference with HITRAN08: (5  8 (2  ))  cm -1 Maki A.G., Wells J.S. NIST Special publication (1991) 821

Determination of the self pressure broadening Ultra high resolution spectra (200 – 1000 points / line) Voigt and Rautian-Sobel'man (hard) line profile Multi-fit procedure Pressure broadening at 2 % accuracy level (2  ) Agrees with HITRAN by 0.6% with Smith by 1.7% (Voigt profile) HITRAN [cm -1 ] HITRAN [cm -1 atm -1 ] This work [cm -1 atm -1 ] (Voigt) This work - HITRAN [%] This work [cm -1 atm -1 ] (Hard) (15) (17) (8) (7) (11) (12) (6) (6) (15) (15) (9) (8) (11) (11) (12) (12) (8) (9) (12) (9) (8)0.68

Air-pressure broadening coefficients 8 absorption spectra recorded with the crossed UV-IR cell and a 50 m astigmatic cell (O 3 decomposition <1% / hour) Astigmatic cell HITRAN [cm -1 ]  air [cm -1 atm -1 ] n  air (4) (1) (1) (2) (3) (1) (1) (1) (2) (1) (5) (1) (1)

Voigt profile Air Pressure Shift Temperature dependence: Determination of  air and  air at 240 K → n  air and n  air Temperature regulated cell HITRAN [cm -1 ]  air [cm -1 atm -1 ] (This work)  air [cm -1 atm -1 ] (Smith)  ’  10 5 [cm -1 atm -1 K -1 ] (This work)  ’  10 5 [cm -1 atm -1 K -1 ] (Smith) (1) (1) (1) (1) (7)-2.8(10) (1)0.0007(2)0.5(3) (1) (1)1.40.4(2) (1) (2)-0.6(3) (1) (3)0.1(6) (1) (1)0.6(2) (2) (3)-0.4(4) (1) (1)1.7(2) (2)3.3(4) Smith M. A. H., Malati Devi V., Benner D. C., Rinsland C. P., J. Mol. Spectrosc. 182 (1997)

Conclusion 253 nm UV cross section determination Our IR measurement are 2.2 % higher than HITRAN % inconsistencies between UV (Hearn) and IR (HITRAN 08) recommended values Position in agreement with HITRAN 08 Measurement of temperature dependence of air broadening and air shifting.

Laser spectroscopic study of ozone in the 100←000 band for the SWIFT instrument M. Guinet, C. Janssen, D. Mondelain, C. Camy-Peyret LPMAA, CNRS- UPMC (France) 18/06/2010

Jitter of the Laser diode 3.7  cm -1 The line is used like a frequency/amplitude noise converter

SWI Stratospheric Wind Interferometer FT For Transport studies (SWIFT) Stratospheric wind velocity Doppler effect Wave number  Intensity cm m.s -1 Limb view O 3 à 1133,4 cm -l

J. Reid, D. T. Cassidy, and R. T. MenziesLinewidth measurements of tunable diode lasers using heterodyne and etalon techniques November 1982 / Vol. 21, No. 21 / APPLIED OPTICS Exemple of TDL Line Shape : Repeatability of the determination of the laser line shape Set of 32 (on two day) measure in a sealed N 2 O cell The intensity,  lorentz (2  cm -1 ),  gaussian (4  cm -1 ) are fit on the spectrum ± 4%  lorentz Intensity ± 9‰ ParameterSD intensity9‰9‰  lorentz  gaussian 4% 5% Source of biasEffect on the intensity mean value ( ± 1.6 ‰)  lorentz fix to it’s mean value 0.7‰  gaussian fix to it’s mean value 0.3 ‰ 4% on  lorentz 5% on  gaussian 3‰ 1.5‰ We fit the instrument’s apparatus function like a Voigt profile ‰

Stabilized spectrometer Laser Diode UV O 3 Generation system I0I0 FP N2ON2O Accuracy (1  ): Position < cm -1 Intensity < 1%