I. Ventrillard-Courtillot, Th. Desbois, T. Foldes and D. Romanini NO2 trace measurements by Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OF-CEAS) I. Ventrillard-Courtillot, Th. Desbois, T. Foldes and D. Romanini Laboratoire de Spectrométrie Physique, Grenoble, France

NO2 detection… Air-quality monitoring Atmospheric chemistry (precursor of ozone) NOx emission by the snow mantle OF-CEAS advantages: Detection limit < 10-9 cm-1 Spectral resolution: 150 MHz High selectivity on small spectral region (~1 cm-1) Time response <1s Large dynamic: 3 orders of magnitude Real time Simple, compact and robust apparatus NO2 :(from <100 pptv to >100 ppbv) nitrated photolysis induced by intense UV radiation. and more generally Nox (precursor of tropospheric ozone) in traffic areas, rural areas high production of NOx in snow would be due to a photolysis induced by intense UV radiation of the nitrates trapped in the snow chemiluminscence : sensitive (sup PPB) but limited accuracy (Tens of ppb) interference with several species (ozone, HONO…) +sensitivity to environemental conditions (T, humidity)

OF-CEAS : Optical – Feedback CEAS PZT PDsignal Variable attenuator PDref Laser translation Feedback rate : λ/2 + polarizer Feedback phase : PZT V shaped optical cavity => Optical Feedback occurs only at resonances J. Morville, S. Kassi, M. Chenevier, and D. Romanini, Appl. Phys. B, 80, 1027 (2005) Patent WO03031949

Effect of optical feedback narrower spectrum OF induces laser bandwidth narrowing & laser frequency locking to the cavity modes => optimal coupling With optical feedback locking range No optical feedback Laser frequency tuning  Dnlaser ~ 0.1-1 MHz time Laser spectrum T Dncavity~ 10kHz Cavity resonance OF permitting optimal excitation of cavity resonances and temporary laser frequency locking to cavity resonances that allows fast frequency scanning speed and hence high acquisition rate x 10 ! Intensity Cavity transmission

OF-CEAS: detection limits Species 1Hz detection limit [ppb]  [µm] CO2 CO H2S C2H4 CH4 NH3 H2O HCl HF N2O NO2 300 1 100 50 0.5 2 3 1.6 2.3 1.62 1.66 and 2.3 1.53 and 2.3 1.39 1.74 1.3 2.27 0.41 Applications : - Environnement - Industry Medicine Initially developped with DFB (IR) Extended to ECDL (vis) Airbones applications Environnement : mesure de polluants  Industrie: détection de fuites, qualité des gaz, rapports isotopiques,…  Médical : diagnostic non invasif Collaborations : E. Kerstel (Univ. Groningen NL), LSCE (Saclay, Fr), LGGE (Grenoble, Fr), CEA (Saclay, Fr), L. Gianfrani (Caserta, It)… SARA : Business Unit (since 2007)

NO2 detection in the blue ECDL @ 410 nm A. C. Vandaele et al , J. Geophys. Res., 107, 4348 (2002). intense electronic transtions occurs in the visible FT resolution 0.1cm-1 (150MHz=>0.005cm-1 : 20 fois plus resolu) ECDL are compatible with OF-CEAS I. Courtillot et al, Appl. Phy. B (2006) V. Motto-Ross et al, Appl. Phy. B (2007)

NO2 portable OF-CEAS spectrometer Temperature stabilized Acoustic and mechanical insulation 65 cm V-Shape Cavity : - 3 Mirrors, 1m ROC - R= 99.991% ( F =35 000) - L = 2x50 cm V cavity 50 cm Insulated from acoustic and mechanical vibrations Coil spring for optimum stability the cavity is made of… V grooves where drilled input gaz flow is obtained from dry nitrogen in which is injected a fraction of NO2 diluted sample Teflon tubes Gas circulation-system : - Pressure controller (100 mbar) Rotary vacuum pump Calibrated NO2 samples : NO2 standard (8.69 +/-0.43 ppm) Dilution in pure dry N2 with 2 high precision flux controllers (1,2) Allows dilution down to 30 ppb of NO2 (@ total flux of 0.25 L/min) Temperature stabilized Pressure regulation: 100mbar Flux: 0.1 – 0.3 L/mn N2 pump NO2 (8.69 ppm +/-0.43 ppm)

Data processing (1) : From raw data to absolute linear absorption reference transmission Cavity transmitted signal NI USB card with labview software

Data processing (1) : involves both CEAS and CRDS CEAS : Transmitted intensity measurements at mode m ( Airy formula) : (1) CRDS : Ring Down at mode k (2) CEAS measurements at each mode m, normalized with CRDS performed at mode k : NI USB card with labview software (1) & (2) => where:

Data processing (2) : From  to NO2 concentration Fit of a single spectrum (100ms) Real-time multilinear fit : Reference NO2 spectrum Baseline (polynomial) absolute linear absorption Real-time multilinear fit of the linear absorption adjusting the coefficients of No spectra found in the literature NO2 spectrum has to be previously saved by OF-CEAS with a calibrated sample OF-CEAS spectral resolution: 150 MHz Reference spectrum has to be acquired by OF-CEAS

Sensitivity Deduced from fit residuals:  ~ 2 - 4 x 10-10 cm-1 150 - 300 ppt @100mbar From cNO2 values:  ~ 2 - 5 ppb Present limitation: Stability of the signal (attributed to the optical setup) Deduced from NO2 concentration measurements (0 to 2ppm) typical values: residual unexpected OF Standard deviation Concentration values

Linearity Deviation < 10% Offset : 40ppb Error bars correspond to standard deviation (20 ppb) Y scale) and are derived from flux controllers accuracy (X scale, 2% max). Stability ~2% over 7hours Deviation of 7% between measurements and expected values from calibrated samples Deviation < 10% Offset : 40ppb Reproducibility over 8 hours ~ 5% Wall effects to be minimized

Conclusions NO2 detection @100mbar: Linearity and accuracy better than 10% Sensitivity : Limited by signal fluctuations: 3 ppb in 0.1s A gain of a factor 10 seems achievable: 200ppt in a single scan (0.1s) to conclude we can say that OFCEAS offers sucessive injection of TEM00 modes yield a mode by mode spectrum separated by the FSR

Perspectives Optics : Investigation of instability of the signal (etaloning effects, small change in the coupling efficiency… ) Gaz : Special coating of tubes and cavity (Sulfinert®) Concentrations samples below 100ppb (permeation tube) Higher pressure studies: averaging over a small spectral region (renounce to spectral selectivity) Metal passivation Present limitations stability of the signal: OF pendant le RD diferent d’un spectre à l’autre car le pzt bouge Bcp plu ssensible au OF que DFB car taux de rtroaction beaucoup plus eleve ~20-50% contre 1% In-situ measurements in remote areas, in the frame of studies on NOx emitted by the snow mantle. Restek’s proprietary Sulfinert® passivation technique bonds an inert silica layer into the surface of the stainless steel, preventing active compounds from reacting with or adsorbing to the stainless steel.

Cavity Enhanced Absorption Spectroscopy (CEAS) L Effective absorption length ~ L . F with F > 10 000 laser photodiode Gas sample Mirror R>99.99% PD signal : modified transmission frequency t(n) t0 time CRDS CEAS CO (0.5 ppm) CH4 (9 ppm) Données breath analysis Parler ici du fit multi composantes à partir des données HITRAN Spectra self-calibrated by CRDS (Cavity Ring-Down Spectroscopy)

OF-CEAS : Cavity transmission signal the frequency locking range can be adjust to nearly match an FSR Frequency monitoring with a thick uncoated etalon (1 GHz)

OF-CEAS spectrometer for in-situ measurements Quantitative and selective measurements Free from calibration with a reference gaz sample (CRDS) Response time < 1s Analysed gaz sample : 18 cm3 Flux : 0.1 – 0.4 L/min Pressure : 100 - 400 mbar Transfert de technologie, réalisation d’appareils : pour des labo ou transfert techno avec des partenariats industriel 30kg, rack + 1 pompe et un ordi Spectroscopie par amplification resonante d’absorption SARA : Business Unit (since 2007) Collaborations : E. Kerstel (Univ. Groningen NL), LSCE (Saclay, Fr), LGGE (Grenoble, Fr), CEA (Saclay, Fr), L. Gianfrani (Caserta, It)…

OF-CEAS : L’appareil

OF-CEAS spectrometer for in-situ measurements Collaborations : E. Kerstel (Univ. Groningen NL), LSCE (Saclay, Fr), LGGE (Grenoble, Fr), CEA (Saclay, Fr), L. Gianfrani (Caserta, It)…

OF-CEAS: gaz and detection limits Species 1Hz detection limit [ppb]  [µm] Carbon dioxide CO2 300 1.6 Carbon monoxide CO 1 2.3 Hydrogen sulfide H2S 100 Ethylene C2H4 50 1.62 Methane CH4 0.5 1.66 and 2.3 Ammonia NH3 2 1.53 and 2.3 Water (vapor) H2O 1.39 Hydrochloric acid HCl 1.74 Hydrofluoric acid HF 1.3 Nitrous oxide N2O 2.27 Nitrogen dioxyde NO2 5 0.41 Applications : - Environnement - Industry Medicine Initially developped with DFB (IR) Extended to ECDL (vis) Environnement : mesure de polluants  Industrie: détection de fuites, qualité des gaz, rapports isotopiques,…  Médical : diagnostic non invasif Collaborations : E. Kerstel (Univ. Groningen NL), LSCE (Saclay, Fr), LGGE (Grenoble, Fr), CEA (Saclay, Fr), L. Gianfrani (Caserta, It)… SARA : Business Unit (since 2007)

NO2 portable OF-CEAS spectrometer PD1 ECDL PD2 PZT l/2 V-cavity Pump 2 1 NO2 8.69 ppm N2 inlet outlet Pressure controller