A.Cuisset, D.Bigourd, G. Mouret, S. Matton, F. Hindle, E. Fertein, R. Bocquet Laboratory of Physics and Chemistry of the Atmosphere, UMR CNRS 8101, Université du Littoral Côte d’Opale, Dunkirk  Bigourd & al., Optics Letters, vol. 31 n°6, (August 2006)

 The smoke matrix has been shown to be composed of ~ 4000 compounds distributed between the gas and the aerosol phases R.R Baker, “ Smoke chemistry, ” in TOBACCO Production, Chemistry and Technology, D.L. Davis, M.T. Nielson, eds. (Blackwell Science, London, 1999), Chapter 12, pp Standard analytical chemistry techniques (chromatography, mass spectroscopy…) Experimental techniques employed for the mainstream smoke analysis These methods generally require:  a sampling method to capture the gas phase  a comparison with a standard of calibration  a detection technique adapted to the system study Optical spectroscopy in the infrared region (tunable diode lasers, quantum cascade lasers…)  Direct in situ measurements in gas phase with a limited tuning range.  Translation of the measured fractional absorption into absolute concentration not always straightforward into absolute concentration not always straightforward

 THz linear absorption spectroscopy gives very precise fingerprints of numerous light polar molecules accessing their rotational spectrum.  The translation of the measured fractional absorption into absolute concentration does not require the use of a calibration gas, provided that the spectral parameters are well known.  Molecular information may be obtained in diffusive media ( fog, dust, smoke, flames..) generally opaque at the IR wavelengths.  Possibility of highly selective measurements with weak Doppler contribution of the broadening. Detection and quantification of molecular species in the cigarette smoke Advantages of the THz radiation

Broadband analysis of the smoke using THz-Time Domain Spectroscopy Broadband radiation from 100 GHz to 1300 GHz Rapid (few minutes) and simultaneous detection of several rotational lines of hydrogen cyanide, carbon monoxide and water on more one decade of frequency  Low-resolution of the spectrum (2.2 GHz) and strong overlapping between the lines.  Improved spectral resolution can be obtained by CW difference-frequency photomixing H 2 O HCN  CO P=950 hPa

V Continuous-wave optical lasers THz radiation at the beat note frequency  THz =  2 -  1 Photomixer  2   1 Semi-conductor carrier lifetime Antenna cut off frequency  Mixing of two focused laser beams in a semiconductor-based photomixer  Spectral purity of the source limited by the optical laser sources.

Sa:Ti laser  810 nm 10 W Verdi Fiber 4 K Si bolometer Photomixer + Silicium Lens 10 W Verdi Sa:Ti laser  810 nm Absorption cell polarizer /2 chopper Lock-in amplifier The two continuous lasers are monitored by the autoscan systems (Coherent Inc) 8 µm Spiral antenna connected to the electrodes LT-GaAs substrate Institut of Electronic, Microelectronic and Nanotechnology Université des Sciences et Technologies, Lille Collaboration with the

Spectral coverage : GHz continuously Spectral coverage : GHz continuously Power emitted: 800 nW at 200 GHz, 2 nW at 1 THz and 0.1 nW at 2 THz Power emitted: 800 nW at 200 GHz, 2 nW at 1 THz and 0.1 nW at 2 THz Sensitivity :  min ≈10 -3 cm -1 at 500 GHz,  min ≈ cm -1 at 1 THz Sensitivity :  min ≈10 -3 cm -1 at 500 GHz,  min ≈ cm -1 at 1 THz Spectral purity : 5 MHz Spectral purity : 5 MHz Frequency limit ≈ 3THz Frequency resolution ≈ 5MHz  Rotational spectrum of hydrogen sulfide H 2 S (P=0.15 hPa)

T = 294 K, P=20 hPa  Thanks to the large tunability of the laser sources, HCN, CO and H 2 O rotational lines were straightforward assigned Spectrum obtained by a long scan (~ 80 min.) of the CW-THz spectrometer  Broad and narrow absorptions of H 2 O originates from ambient water vapor ( P~1013 hPa) and from the water present in the smoke ( P~20 hPa), respectively.  All the J  J+1 transitions of HCN with 5<J<26 and CO with 4<J<20 have been clearly assigned in the 620 – 2300 GHz frequency range Natural aspiration of the smoke by the evacuated cell

 Thanks to the good spectral purity of the CW-THz source, the transitions line shapes allowed to determine the concentrations of the detected species.  Lorentzian fit on the J=14 - J=13 transition of HCN Pure lorentzian fit :  At P = 20 hPa (  ) collisional >> (  ) Doppler  Air-broadening coefficient and line position from spectroscopic database were used.  Results obtained from the intensity measurement of HCN and CO lines:  An average value of 210 ppm per cigarette for the HCN concentration with a standard error of 11 ppm (taking into account the different fits)  In the same manner for CO, a concentration of 1.7 % with a standard error of 0.3 % per cigarette was measured. 0.3 % per cigarette was measured.  The minimum detectable concentrations (at a SNR=1) was estimated to be 9 ppm for HCN and 0.1 % for CO

 H 2 CO was detected in the cigarette smoke only at low pressure (< 5 hPa). P=0.7 hPa P=0.5 hPa Numerous strong intensity lines of H 2 CO have been detected and assigned in the 1000 GHz and 1500 GHz  An average concentration of 386 ppm estimated from the profile line shapes is not considered representative of the cigarette smoke for several reasons: Adsorption onto the cell’s interior surface Distorsion of the measured line profile

Collaboration with the C. C. M. (Centre Commun de Mesures) Collaboration with the C. C. M. (Centre Commun de Mesures) : F. Cazier H. Naouili D. Dewaele Standard analytical chemical methods currently used for each compounds detected MoleculeChemical analysis method Masse per cigarette deduced from the chemical analysis Masse per cigarette measured by CW-THz spectroscopy CO Commercial instrument based on infrared absorption measurement 109 mg90 mg HCN Dosage of the anions CN - by a colorimetric method. >13.4 µg1050 µg H 2 CO HPLC with UV detection in a DNPH solution µg> 16 µg NH 3 Dosage of the cations NH 4 + by ion chromatography using conductivity detectors < 0.4 µg < 289 µg  The chemical methods requires a sampling method to capture the gas phase species, the comparison with a standard of calibration and a detection technique adapted to the molecular system studied.  As in the case of the dosage of CN - anions, other compounds present in the smoke may interfered with the compound targeted.

 Detection and quantification of several small polar compounds in a complex and diffusive medium: the mainstream cigarette smoke  Capabilities of trace gas detection at the ppm level for highly polar molecules in an environment considered as one of the most important indoor air pollutants. Application of environmental monitoring by CW-THz spectroscopy in a realistic situation where a large number of compounds are present. Furthers studies of the cigarette smoke by THz spectroscopy.  Improvement of the spectrometer sensitivity using a multipass cell in order to detect additional polar components as acetaldehyde, acrolein, formic acid, acetone…  Changing the cigarette combustion process in order to reproduce the true inhalation of a smoker.  Application of THz spectroscopy in the measurement of breath trace compounds